Association between migration and severe maternal outcomes in high-income countries: Systematic review and meta-analysis

Maxime Eslier; Elie Azria; Konstantinos Chatzistergiou; Zelda Stewart; Agnès Dechartres; Catherine Deneux-Tharaux

doi:10.1371/journal.pmed.1004257

. 2023 Jun 22;20(6):e1004257. doi: 10.1371/journal.pmed.1004257

Association between migration and severe maternal outcomes in high-income countries: Systematic review and meta-analysis

Maxime Eslier ^1,^*,^#, Elie Azria ^1,^2,^#, Konstantinos Chatzistergiou ², Zelda Stewart ¹, Agnès Dechartres ³, Catherine Deneux-Tharaux ¹

PMCID: PMC10328365 PMID: 37347797

Abstract

Background

Literature focusing on migration and maternal health inequalities is inconclusive, possibly because of the heterogeneous definitions and settings studied. We aimed to synthesize the literature comparing the risks of severe maternal outcomes in high-income countries between migrant and native-born women, overall and by host country and region of birth.

Methods and findings

Systematic literature review and meta-analysis using the Medline/PubMed, Embase, and Cochrane Library databases for the period from January 1, 1990 to April 18, 2023. We included observational studies comparing the risk of maternal mortality or all-cause or cause-specific severe maternal morbidity in high-income countries between migrant women, defined by birth outside the host country, and native-born women; used the Newcastle–Ottawa scale tool to assess risk of bias; and performed random-effects meta-analyses. Subgroup analyses were planned by host country and region of birth.

The initial 2,290 unique references produced 35 studies published as 39 reports covering Europe, Australia, the United States of America, and Canada. In Europe, migrant women had a higher risk of maternal mortality than native-born women (pooled risk ratio [RR], 1.34; 95% confidence interval [CI], 1.14, 1.58; p < 0.001), but not in the USA or Australia. Some subgroups of migrant women, including those born in sub-Saharan Africa (pooled RR, 2.91; 95% CI, 2.03, 4.15; p < 0.001), Latin America and the Caribbean (pooled RR, 2.77; 95% CI, 1.43, 5.35; p = 0.002), and Asia (pooled RR, 1.57, 95% CI, 1.09, 2.26; p = 0.01) were at higher risk of maternal mortality than native-born women, but not those born in Europe or in the Middle East and North Africa. Although they were studied less often and with heterogeneous definitions of outcomes, patterns for all-cause severe maternal morbidity and maternal intensive care unit admission were similar. We were unable to take into account other social factors that might interact with migrant status to determine maternal health because many of these data were unavailable.

Conclusions

In this systematic review of the existing literature applying a single definition of “migrant” women, we found that the differential risk of severe maternal outcomes in migrant versus native-born women in high-income countries varied by host country and region of origin. These data highlight the need to further explore the mechanisms underlying these inequities.

Trial Registration

PROSPERO CRD42021224193.

In a systematic review and meta analysis of data obtained from 35 studies, Maxime Eslier and colleagues synthesize and compare the risk of severe maternal outcomes in high income countries between migrant and native-born women, overall and by host country and region of birth.

Summary

Why was this study done?

Some studies conducted in high-income countries report that the risk of maternal mortality and severe maternal morbidity is higher for migrant than native-born women, while other studies do not.
Whether this heterogeneity is related to differences in the definition and measurement of migration and of maternal outcomes or to real differences between settings remains unclear.

What did the researchers do and find?

In this literature review including 35 studies, we found that, in high-income countries, the differential risk of severe maternal outcomes in migrant women, defined as born outside the host country, compared to native-born women, varied by the host country and the migrant women’s region of birth.
In Europe, migrant women were generally at higher risk of severe maternal outcomes than native-born women, whereas the risks for migrant women did not differ significantly from those for native-born women in United States of America or Australia.
Among migrant women, those born in sub-Saharan Africa, in Latin America and the Caribbean, or in Asia were at higher risk of severe maternal outcomes than their native-born counterparts, while those born in Europe or in the Middle East and North Africa were not.

What do these findings mean?

When a single definition of “migrant” women was applied, the differential risk of severe maternal outcomes in migrant versus native-born women in high-income countries varied by host country and region of origin.
These data highlight the need to further explore the mechanisms underlying these inequities.
Future studies should use harmonized definitions for all-cause and cause-specific severe maternal morbidity and take into account other social factors such as race/ethnicity, migrant women’s administrative status, and economic factors that may interact with migration to understand the inequalities in maternal health between migrant and native-born women.

Introduction

Economic crises, wars, natural disasters, and increased inequalities between countries have generated significant migration waves. Over the past decade, the migrant population has increased by 23% in countries belonging to the Organisation for Economic Co-operation and Development [1] and by 28% in the European Union [2]. These movements, involving large proportions of young adults, women in particular [2], result in increasing the proportion of births to foreign-born women in their host countries. In Europe, every fourth birth is to a foreign-born mother, although this rate varies substantially across countries [3,4]. This trend presents organizational and cost challenges for the host health systems, especially as migrant women appear to be more vulnerable and to have greater social and health needs than native-born women [5,6].

Because the scientific literature on the association between migration and severe maternal outcomes is heterogeneous and inconclusive, it cannot accurately inform public policies or healthcare provision [7]. Some studies in high-income countries have reported higher risks of maternal mortality and severe maternal morbidity among migrant women than native-born women [8–13], while others have not [14–17]. Whether this heterogeneity is related to differences in definitions and methods of measuring migration and maternal outcomes or to real differences between settings remains unclear. Studies have defined migrant women according to their race or ethnicity [18–23], nationality [24–27], or their birthplace [14,16,17,28–33]. A few others have used other criteria, such as the Human Development Index of the country of origin [34], length of residency in the host country, or legal status [35]. The Reproductive Outcomes and Migration (ROAM) collaboration and the EURO-PERISTAT project recommended that maternal country of birth be used to study immigrants’ perinatal health [36]. The severe maternal outcomes targeted and their definitions also vary greatly across studies. Moreover, because much of the available literature is based on routinely collected data coded by the International Classification of Diseases (ICD), severe maternal outcomes might well be misclassified [14,15,17,37–43]. A previous review and meta-analysis of data from Western European countries between 1970 and 2013 showed that migrant women have a risk of maternal mortality twice that of women born in the host country [8]. Its results were nonetheless limited by the important heterogeneity in the definitions of migrant women across studies and the inclusion of old data. Another systematic review also conducted on European studies compared the risk of nonsevere maternal outcomes between 2007 and 2017 for specific subgroups of migrant women only—asylum seekers and undocumented migrant women in Europe. It reported that the risk of maternal mortality and all-cause severe maternal morbidity was higher among asylum seekers than native-born women [35].

Applying a single definition of migrant women, in accordance with international recommendations, we aimed to conduct a systematic review and meta-analysis of available information about the risk of severe maternal outcomes among migrant and native-born women in high-income countries. Differential risk was compared overall and by both host country and migrant women’s region of birth.

Methods

Search strategy and selection criteria

This systematic review and meta-analysis examines studies of the association between migration and severe maternal outcomes in high-income countries. The review protocol was registered with the PROSPERO International Prospective Register of Systematic Reviews, on its website (CRD42021224193), and this article is reported according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines [44].

We searched Medline via PubMed, Embase, and Cochrane Library without language restriction. The search algorithm included relevant Medical Subject Headings (MeSH)/Embase Medical Headings (EMTREE) and free text words combined by Boolean operators for migrant and selected severe maternal outcomes (list below) (S1–S3 Tables). We also screened the reference lists of previous systematic reviews and meta-analyses and of all included studies for any additional references.

We included observational studies published between January 1, 1990 and April 18, 2023, and comparing the risk of severe maternal outcomes between migrant women and native-born women in high-income countries, according to the World Bank classification. Systematic reviews and meta-analyses were included in the first selection by titles and abstracts to allow backward snowballing but excluded in the second selection. Case–control and case studies were excluded. The exclusion of studies before 1990 aimed to limit the heterogeneity in migrant women’s characteristics and host countries’ integration policies that could be caused by too long a study period.

Our review included studies that defined migrant women as women born outside the host country and compared them with women born in the host country, in accordance with international recommendations [36,45,46]. The severe maternal outcomes studied were maternal mortality, all-cause severe maternal morbidity, and cause-specific severe maternal morbidity, during pregnancy and up to 1 year after delivery. The specific causes of severe maternal morbidity included were severe postpartum hemorrhage, eclampsia, severe sepsis, and uterine rupture, as well as maternal intensive care unit (ICU) admission and near misses, as defined by the World Health Organization (WHO) [47]. This review did not consider maternal mental health outcomes because we believe they require a specific assessment and because a systematic review on this topic was registered as underway when we started (PROSPERO, CRD42021226291) and finally published [48].

We used Covidence systematic review software (Veritas Health Innovation, Melbourne, Victoria, Australia) to screen and extract data. Two reviewers (ME and KC) independently screened first the titles and abstracts of the retrieved studies to exclude those that were irrelevant and then the full text of the remaining studies to assess eligibility for inclusion. Disagreements were resolved through discussion with the help, if necessary, of a third author (EA or CDT) to reach a consensus. Reasons for exclusion were recorded. The corresponding author of unavailable articles was contacted by email to request the full text version.

Data analysis

The same reviewers (ME and KC) independently extracted the following characteristics for each included study: general study information (authors’ names, year of publication, journal, language, funding); study characteristics (study design, population coverage, inclusion period, host country, and data source for the exposure of interest and for outcomes); characteristics of the study population (total number of women, inclusion/exclusion criteria); outcomes evaluated (mortality and/or all-cause severe maternal morbidity and/or cause-specific severe maternal morbidity); number of cases overall, in each subgroup and for each outcome of interest; and items to assess methodological quality. We contacted corresponding authors to obtain additional data not available in the original publication.

Two authors (ME and KC) used the Newcastle–Ottawa scale for observational studies to assess the methodological quality of each study and based their assessment on the following categories of items: selection of study groups, comparability of groups, and ascertainment of the outcome of interest [49]. The threshold for defining a high-quality study was a score ≥7 [50].

An unadjusted risk ratio for each outcome was estimated with the number of events and of migrant women and native-born women reported in each study. We did not estimate adjusted risk ratios because this study examined the differential risk between migrant women and native-born women and not causal mechanisms. Between-study heterogeneity was explored by visual examination of the forest plots and by the heterogeneity test and I² statistic with its 95% confidence interval (CI) [51,52]. Because heterogeneity was expected on scientific grounds, we used random-effects meta-analysis models with the DerSimonian and Laird method [51] and decided, when relevant, not to provide an overall assessment and to combine data only within subgroups. Those subgroups were defined according to the host country (European countries, the United States of America (USA), Canada, and Australia), the migrant women’s regions of birth (Europe, the Middle East and North Africa, sub-Saharan Africa, Latin America and the Caribbean, and Asia and the Pacific), the migrant women’s legal status (migrant women with host country nationality, legally resident migrant women without host country nationality, and undocumented migrant women), and the Newcastle-Ottawa scale score. We tested the interaction between the exposure of interest and the variables defining subgroups. The considerable heterogeneity in definitions of cause-specific severe maternal morbidity prevented the performance of any quantitative meta-analysis for these outcomes.

We assessed small-study effects with funnel plots when there were sufficient studies (n > 10).

Analyses were done with Review Manager Software (version 5.4.1).

Results

Characteristics and methodological quality assessment

Of the 2,290 records screened, 185 were relevant for full-text review and 39 were finally included (Fig 1). The appendix provides a list of excluded studies with the reasons for their exclusion (S4 Table). The leading reason for exclusion was the absence of a definition of migration based on region of birth, followed by outcomes outside the scope of our review.

Table 1 shows the characteristics of the 35 studies from Europe, Australia, the USA, and Canada that furnished 39 reports. Because 4 studies yielded several reports covering different outcomes or different subgroups of migrant women, we included 39 reports overall. The median year of publication was 2017 (range 2008 to 2022). Half the studies used the ICD or procedure codes to define their outcomes (Tables 1 and S5). The assessment of the quality of the studies included is presented in the appendix (S6 Table). According to the Newcastle–Ottawa scale score, only 1 study had a low methodological quality that limited the relevance of the subgroup analysis (Tables 1 and S6). Because only 3 studies contained information about legal status, we did not perform the corresponding subgroup analysis (Table 1).

Table 1. Characteristics of included studies.

Total = 35 studies
First year of inclusion period, median (min-max)		2007 (1988–2016)
Last year of inclusion period, median (min-max)		2012 (2005–2019)
Host country, n (%)
	Australia	7 (20)
	United States of America	5 (14)
	France	4 (11)
	Canada	4 (11)
	the Netherlands	3 (9)
	United Kingdom	3 (9)
	Sweden	2 (6)
	Denmark	2 (6)
	Germany	2 (6)
	Norway	1 (3)
	Spain	1 (3)
	Italy	1 (3)
	Multicountry	1 (3)
Study population, n (%)
	National	21 (60)
	Regional	9 (26)
	Mixed (National and Regional)	1 (3)
	Multicenter	2 (6)
	Single-center	3 (9)
Study design, n (%)
	Cohort study	19 (54)
	Cross-sectional study	17 (49)
*Source of information regarding exposure of interest^, n (%)**
	Birth and/or death certificates	29 (83)
	Birth register	4 (11)
	Interview	1 (3)
	Medical file	1 (3)
	Self-administered questionnaire	1 (3)
Legal status available, n (%)		3 (9)
Reported outcome, n (%)
	Maternal mortality	17 (49)
	All-cause severe maternal morbidity	10 (29)
	Maternal near miss	3 (9)
	Maternal intensive care unit admission	5 (14)
	Eclampsia	4 (11)
	Severe postpartum hemorrhage	6 (17)
	Severe sepsis	4 (11)
	Uterine rupture	8 (23)
Definition of outcome, n (%)
	Clinical criteria specifically collected	18 (51)
	Existing ICD or procedure codes	18 (51)
Source of information regarding outcome, n (%)
	Medico-administrative data	15 (43)
	Medical file	19 (54)
	Birth register	2 (6)
Newcastle–Ottawa scale score, median (min-max)		7 (6–8)

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*Migrant women defined by region of birth.

Maternal mortality

Seventeen highly heterogeneous studies included data on maternal mortality (S1 Fig). In European host countries, migrant women were at higher risk of maternal mortality than native-born women (pooled risk ratio [RR] 1.34; 95% CI, 1.14, 1.58; p < 0.001; I² = 58%; 95% CI; 18, 79), with RRs ranging from 0.77 (95% CI, 0.15, 3.80) to 2.01 (95% CI, 1.53, 2.65), whereas no excess risk was observed in the USA or Australia (p for interaction < 0.001) (Fig 2). Some subgroups of migrant women were at higher risk of maternal mortality than their native-born counterparts. They included women born in sub-Saharan Africa (pooled RR, 2.91; 95% CI, 2.03, 4.15; p < 0.001; I² = 57%; 95% CI, 0, 83), in Latin America and the Caribbean (pooled RR, 2.77; 95% CI, 1.43, 5.35; p = 0.002; I² = 82%; 95% CI; 53, 93), and in Asia (pooled RR, 1.57; 95% CI, 1.09, 2.26; p = 0.01; I² = 31%; 95% CI, 0, 74). Women born in Europe or in the Middle East and North Africa, on the other hand, were not at higher risk (p for interaction < 0.001) (Fig 3). Among European countries, the United Kingdom, Denmark, Norway, and Spain presented a particular pattern, with no significant excess risk of maternal mortality for migrant women considered globally (Fig 2), but specific subgroups studied according to their region of birth did show such an excess risk compared to native-born women (Fig 3).

Fig 2 — Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Deneux-Tharaux et al. 2017 [29]; Saucedo et al. 2021 [53]; Knight et al. 2015 [54]; Knight et al. 2017 [55]; Knight et al. 2020 [56]; Diguisto et al. 2022 [57]; Esscher et al. 2013 [28]; Garcia-Tizon Larroca et al. 2022 [58]; Schutte et al. 2009 [32]; Kallianidis et al. 2022 [59]; Johnson et al. 2014 [60]; Humphrey et al. 2015 [61]; Humphrey et al. 2017 [62]; Humphrey et al. 2020 [63]; Creanga et al. 2012 [16]; Singh et al. 2021 [14]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Fig 3 — Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Deneux-Tharaux et al. 2017 [29]; Saucedo et al. 2021 [53]; Knight et al. 2015 [54]; Knight et al. 2017 [55]; Knight et al. 2020 [56]; Garcia-Tizon Larroca et al. 2022 [58]; Schutte et al. 2009 [32]; Kallianidis et al. 2022 [59]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

All-cause severe maternal morbidity

Similar patterns were found for both all-cause severe maternal morbidity and maternal ICU admission. The meta-analysis of the former included 10 studies comparing migrant women and native-born women with substantial heterogeneity (Figs 4, 5 and S2). The pooled relative risk of all-cause severe maternal morbidity in migrant women compared to native-born women was 1.19 (95% CI, 0.95, 1.49; p = 0.1; I² = 87%; 95% CI, 69, 95) in European host countries and 0.99 (95% CI, 0.95, 1.03; p = 0.7; I² = 83%; 95% CI, 64, 92) in the USA and Australia (p for interaction < 0.001) (Fig 4). Among migrant women, those born in sub-Saharan Africa (pooled RR, 1.54; 95% CI, 1.26, 1.88; p < 0.001; I² = 88%; 95% CI, 72, 95) or in Latin America and the Caribbean (pooled RR, 1.14; 95% CI, 1.05, 1.25; p = 0.003; I² = 51%; 95% CI, 0, 84) were at higher risk of all-cause severe maternal morbidity than their native-born counterparts, while those born in Europe or the Middle East and North Africa were not (p for interaction < 0.001) (Fig 5).

Fig 4 — Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65], and 2011 [66]; Van Hanegem et al. 2011 [67]; Zanconato et al. 2012 [33]; Urquia et al. 2015 [40] and 2017 [15]; Wanigaratne et al. 2015 [41]; Jairam et al. 2023 [68]; Mujahid et al. 2021 [17]; Wall-Wieler et al. 2020 [42]; Leonard et al. 2021 [37]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Fig 5 — Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Eslier et al. 2022 [64]; Urquia et al. 2015 [40] and 2017 [15]; Wanigaratne et al. 2015 [41]; Jairam et al. 2023 [68]; Zwart et al. 2008 [9], 2010 [65], and 2011 [66]; Van Hanegem et al. 2011 [67]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Cause-specific severe maternal morbidity

Only a few studies considering specific causes or conditions of severe maternal morbidity were available (Figs 6–11). The synthesis of their results was difficult given the persisting heterogeneity in outcome definitions, except for maternal ICU admission (Fig 6). Three of 5 studies reported that migrant women were at higher risk of maternal ICU than native-born women with relative risks ranging from 1.34 (95% CI, 1.23, 1.46) to 1.97 (95% CI, 1.55, 2.52) (Figs 6 and S3). Migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, and in Asia were also at higher risk of maternal ICU admission than native-born women, but those born in Europe or in the Middle East and North Africa were not (p for interaction < 0.001) (S4 Fig).

Fig 6 — The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Medcalf et al. 2016 [38]; Turner et al. 2020 [69]; Gulersen et al. 2022 [70]. CI, confidence interval; df, degrees of freedom; ICU, intensive care unit; IV, inverse variance; RR, risk ratio.

Fig 11 — The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2020 [31] and 2022 [64]; Wahlberg et al. 2013 [72]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Urquia et al. 2015 [40] and 2017 [15]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Fig 7 — The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: David et al. 2019 [71]; Wahlberg et al. 2013 [72]; Reime et al. 2012 [73]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Fig 8 — The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Reime et al. 2012 [73]; Urquia et al. 2014 [39] and 2017 [15]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Fig 9 — The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2020 [31]; Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Reime et al. 2012 [73]; Flood et al. 2019 [74]; Turner et al. 2020 [69]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

Fig 10 — The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2022 [64]; Wahlberg et al. 2013 [72]; Reime et al. 2012 [73]; Urquia et al. 2017 [15]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.

A funnel plot was performed only for maternal mortality, as it was the only outcome for which a sufficient number of studies was available. It suggests a small-study effect (S5 Fig), which may be partly explained by the heterogeneity across host countries (S6 Fig).

Discussion

In high-income countries, the differential risk of severe maternal outcomes between migrant and native-born women, defined as women born outside and in the host country, varied by both host country and the migrant women’s region of birth. Migrant women in European host countries were at higher risk of severe maternal outcomes than native-born women, while migrant women in the USA and Australia did not differ from those born there for such outcomes. Migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, or in Asia were at higher risk of severe maternal outcomes than the women born in their host countries, but those born in Europe or in the Middle East and North Africa were not.

Our systematic review shows that migrant women living in European host countries had a higher risk of severe maternal outcomes than the native-born women, while migrant women in the USA and Australia did not. The social structure of the native-born groups is a hypothesis that might explain this disparity between these high-income settings. In the USA and Australia, the groups with the highest maternal mortality and morbidity rates are, respectively, Black [75] and indigenous [60–63] women, both included in the native-born reference group. The maternal mortality ratio is from 3 to 6 times higher in Black than in White women in the USA [76] and in indigenous versus nonindigenous women in Australia [60–63]. Furthermore, the overall maternal mortality ratio in the USA is more than twice as high as in Europe, and this ratio for native-born US White women is double that for native-born Europeans [53,55,76]. In both the USA and Australia, therefore, the subgroups at risk of severe maternal complications appear to be related more to race or ethnicity than to migrant women’s region of birth. Thus, in these contexts, the comparison between “native” and “foreign-born” populations does not take into account the colonial history and migratory backgrounds of the now “native” populations that played a role in determining these groups’ social position and their health status.

Another interesting finding is that migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, and in Asia were at higher risk of severe maternal outcomes than the corresponding native-born women of the host country, although migrant women born in Europe or in the Middle East and North Africa were not. Notably, the particular pattern observed in the United Kingdom, with no significant excess risk in migrant women versus native-born women globally, when we did not consider region of birth, highlights the importance of studying migration according to this factor. One hypothesis for this differential risk among subgroups of migrant women is that the specific migration contexts and paths of these subgroups do not carry the same risks. Migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, and in Asia have usually lived in the host country for less time and are more frequently disadvantaged by a language barrier, lack of legal status, social isolation, and poor housing conditions, compared with other categories of migrant women [5,28]. These cofactors may result in a more difficult access to healthcare system, especially prenatal care, which is known to be inadequate more often, in both quantity and quality, among these geographical subgroups [77,78]. Researchers have explored the association between severe maternal outcomes and other categorizations of migrant women’s native countries, besides geography. One study using the World Bank classification of economies found a higher risk of maternal near misses in migrant women from low-income countries and not in those from middle- or high-income countries, compared with women born in Sweden [72]. A Spanish study used the Human Development Index of countries to report that maternal death rates were higher for migrant women from countries with the lowest Human Development Index [58]. We could not include these analyses in our review since each was unique in its categorization. These approaches, however, provide interesting insights into the causal mechanisms of health disparities among migrant women.

Another explanatory hypothesis for the differential risk we found according to the migrant women’s region of birth is the possibility of discrimination against some subgroups of migrant women with physical (e.g., black skin) or cultural singularities that might activate bias among healthcare professionals and lead to differential care [13,79–81]. These discriminations may originate from individual attitudes through explicit or implicit bias but could also be driven by structural racism [82,83]. An approach that focuses on the migration issue and takes the fact of being born abroad as the only exposure variable cannot by itself provide an insight into the mechanisms of social inequalities in health between migrant and native-born women. This approach is necessary and, in our opinion, justifies the studies thus far conducted in this way and included in this systematic review. It cannot, however, be sufficient. Maternal health is influenced by the complex interaction of multiple social factors. Among these factors, socioeconomic determinants, such as migrant women’s administrative status, should be considered and analyzed as potential intermediate factors. Race/ethnicity, a major determinant in contexts such as the USA or Australia, even when migration is the main focus of the studies, should also be collected and included in the analysis to enable multidimensional descriptions of the groups being compared and provide deeper insight to the causal relationships with health outcomes.

To our knowledge, this is the first systematic review and meta-analysis focusing on the association of migrant women and native-born women in high-income countries with various severe maternal outcomes and according to a single and consensual definition of migrant women. In contrast to previous systematic reviews, we have included all data available from high-income countries and not only those in Europe [8,35]. This offers the opportunity to compare national contexts with various migration demographic patterns, as well as various public policies related to migration. Use of this single, consensual definition makes it possible to address migration issues specifically, separate from overall ethnic or racial disparities, although the ethnic/racial dimension is probably one of the mechanism involved in the disparities faced by migrant women [36,45,46]. It also reduced the heterogeneity between studies and improved their comparability. This important heterogeneity in the definitions of migrant women across studies was the main limitation of a previous review and meta-analysis [8]. This definition of migrant women, as being born outside the host country, is the one used by the International Organization for Migration [84] and recommended by the Reproductive Outcomes and Migration collaboration and the EURO-PERISTAT project, to study migrants’ perinatal health [36]. We were able to apply this definition for all included studies except for some Dutch studies [9,65,66] where we cannot exclude that some second-generation migrant women were included in the migrant women group. This definition offers the advantage of targeting a homogeneous group of first-generation migrants. Second-generation migrant women constitute a specific group interesting to study, but databases with available data on the parents’ and grandparents’ countries of birth are still too rare for a synthesis of their results to be useful. Our planned subgroup analyses enabled us to explain a part of the still substantial heterogeneity between studies. In order to explore between-study heterogeneity, we decided to perform subgroup analyses instead of meta-regression with host country and region of birth as moderators because these characteristics are closely related in the set of studies we found, resulting in collinearity in the model, likely to bias the estimates. As a consequence, we cannot totally rule out that host country and region of birth actually characterized the same subgroups of migrant women. Nevertheless, our analysis was still limited by the persistent heterogeneity in definitions of all-cause and cause-specific severe maternal morbidity. Moreover, our review may be limited by the questionable validity of administrative databases because of the uncertain quality of the reporting and the intrinsic limitations of ICD codes—both sources of potential misclassification [43]. Another limitation is that we could not take into account other social factors that may interact with migration to determine maternal health, because many of these data are unavailable. The paucity of studies with data on migrant women’s legal status prevented a subgroup analysis of this variable. Finally, we cannot exclude the risk of selective outcome reporting bias within studies. Researchers may report their findings selectively by choosing to focus on selected outcomes and analyses based on the results [51].

Our findings provide valuable insights for further exploration of the causal mechanisms of maternal health inequalities by highlighting those faced by migrant women in high-income countries according to both their region of origin and the host country. Our analysis was still limited by the persistent heterogeneity in definitions of all-cause and cause-specific severe maternal morbidity. Thus, future studies should use harmonized definitions for all-cause and cause-specific severe maternal morbidity, and future investigations should examine the extent to which specific hypothesized mechanisms, related to the characteristics of the women or the healthcare system, explain the association between migrants and severe maternal outcomes in different settings. Approaches combining the joint characterization and analysis of severe maternal outcomes according to ethnicity, race, and migration could shed light on these question and help to guide policies and care.

To conclude, the differential risk of severe maternal outcomes between migrant women and native-born women in high-income countries varies by the host country and the migrant woman’s region of birth. Our findings highlight the maternal health inequalities faced by migrant women in high-income countries according to their region of origin and host country. Future studies should use harmonized definitions for all-cause and cause-specific severe maternal morbidity and be designed to explore in greater depth the mechanisms of inequalities between migrant women and native-born women.

Supporting information

S1 Table. Literature search algorithm on Medline via PubMed.

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S2 Table. Literature search algorithm on Embase.

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S3 Table. Literature search algorithm on Cochrane Library.

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S4 Table. List of the excluded studies and reasons for their exclusion.

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S5 Table. Characteristics of the included papers, listed in alphabetical order of first authors.

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S6 Table. Methodological quality of the studies included (listed in alphabetical order) assessed with the Newcastle–Ottawa Scale (NOS).

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S7 Table. Amendments made to the protocol PROSPERO.

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S1 Fig. Maternal mortality in migrant women and native-born women.

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S2 Fig. All-cause severe maternal morbidity in migrant women and native-born women.

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S3 Fig. Maternal intensive care unit admission in migrant women and native-born women, stratified by host country.

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S4 Fig. Maternal intensive care unit admission in migrant women and native-born women stratified by migrant women’s region of birth.

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S5 Fig. Funnel plot for studies reporting maternal mortality overall.

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S6 Fig. Funnel plot for studies reporting maternal mortality stratified by host country.

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Acknowledgments

The authors would like to thank Annika Esscher and Birgitta Essén (both from the Department of Women’s and Children’s Health, Uppsala University, Uppsala, Sweden) who supplied data about the number of deaths and maternal mortality ratios for women of reproductive age born in low-, middle-, and high-income countries and in Sweden; Ayesha Siddiqui (Université de Paris, CRESS, Obstetrical Perinatal and Pediatric Epidemiology Research Team, EPOPé, INSERM, INRA, Paris, France) who supplied data about the total number of women diagnosed with severe preeclampsia by distinguishing the women born in France from those born elsewhere in Europe; Baiju Shah (Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Ontario, Canada) who supplied data for the total number of women with and without preeclampsia/eclampsia among each of the nonimmigrant, refugee, and other immigrant groups; Birgit Reime (Faculty of Health Safety Society, Furtwangen University, Furtwangen, Germany) who supplied data for the total number of women diagnosed with cause-specific severe maternal morbidity among native-born and migrant women in Germany between 2001 and 2007; Jessica Turner (Mater Research Institute, University of Queensland, Brisbane, Australia) who supplied data for the total number of women diagnosed with massive postpartum hemorrhage and ICU admission among refugees and women born in Australia; Joost Zwart (Department of Obstetrics and Gynaecology, Deventer Ziekenhuis, 7416 SE Deventer, the Netherlands) and Jos van Roosmalen (Department of Obstetrics and Gynaecology, Leiden University Medical Center, 2300 RC Leiden, the Netherlands) who supplied data for the total number of deliveries among Western and non-Western migrant women; Kjersti Sletten Bakken (Centre for Intervention Science in Maternal and Child Health [CISMAC], Department of Global Public Health and Primary Care, University of Bergen) who supplied data about the total number of women diagnosed with preeclampsia/eclampsia and HELLP syndrome among first-generation immigrants, second-generation immigrants, and native Norwegian-born women; Marcelo Urquia (Department of Community Health Sciences, University of Manitoba Faculty of Health Sciences, Winnipeg, Manitoba, Canada) who supplied data about the total number of women diagnosed with eclampsia according to their region of birth; Miguel-Angel Luque-Fernandez (Department of Non-Communicable Disease Epidemiology, Cancer Survival Group, London School of Hygiene and Tropical Medicine, London; and Department of Non-Communicable Disease and Cancer Epidemiology, Instituto de Investigacion Biosanitaria de Granada (Ibs.GRANADA), University of Granada, Granada, Spain) who supplied data about the total number of live births in Spain and in Europe excluding Spain; Stephanie Leonard (Department of Obstetrics and Gynecology, Stanford University, Palo Alto, California; California Maternal Quality Care Collaborative, Stanford University, Palo Alto, California) who supplied data on the total number of women with severe maternal morbidity, and with non-transfusion severe maternal morbidity in native-born women and migrant women. We would also like to thank Jo Ann Cahn for her English editorial assistance.

Abbreviations

CI: confidence interval
ICD: International Classification of Diseases
ICU: intensive care unit
RR: risk ratio
ROAM: Reproductive Outcomes and Migration
USA: United States of America
WHO: World Health Organization

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

The authors received no specific funding for this work.

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PLoS Med. doi: 10.1371/journal.pmed.1004257.r001

Decision Letter 0

Beryne Odeny

21 Sep 2022

Dear Dr ESLIER,

Thank you for submitting your manuscript entitled "Association between migration and severe maternal outcomes in high income countries: systematic review and meta-analysis" for consideration by PLOS Medicine.

Your manuscript has now been evaluated by the PLOS Medicine editorial staff and I am writing to let you know that we would like to send your submission out for external peer review.

However, before we can send your manuscript to reviewers, we need you to complete your submission by providing the metadata that is required for full assessment. To this end, please login to Editorial Manager where you will find the paper in the 'Submissions Needing Revisions' folder on your homepage. Please click 'Revise Submission' from the Action Links and complete all additional questions in the submission questionnaire.

Please re-submit your manuscript within two working days, i.e. by Sep 23 2022 11:59PM.

Once your full submission is complete, your paper will undergo a series of checks in preparation for peer review. Once your manuscript has passed all checks it will be sent out for review.

Feel free to email us at plosmedicine@plos.org if you have any queries relating to your submission.

Kind regards,

Beryne Odeny

PLOS Medicine

PLoS Med. doi: 10.1371/journal.pmed.1004257.r002

Decision Letter 1

Philippa Dodd

17 Apr 2023

Dear Dr. ESLIER,

Thank you very much for submitting your manuscript "Association between migration and severe maternal outcomes in high income countries: systematic review and meta-analysis" (PMEDICINE-D-22-03069R1) for consideration at PLOS Medicine.

Your paper was evaluated by a senior editor and discussed among all the editors here. It was also discussed with an academic editor with relevant expertise, and sent to independent reviewers, including a statistical reviewer. The reviews are appended at the bottom of this email and any accompanying reviewer attachments can be seen via the link below:

[LINK]

In light of these reviews, I am afraid that we will not be able to accept the manuscript for publication in the journal in its current form, but we would like to consider a revised version that addresses the reviewers' and editors' comments. Obviously we cannot make any decision about publication until we have seen the revised manuscript and your response, and we plan to seek re-review by one or more of the reviewers.

In revising the manuscript for further consideration, your revisions should address the specific points made by each reviewer and the editors. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments, the changes you have made in the manuscript, and include either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please submit a clean version of the paper as the main article file; a version with changes marked should be uploaded as a marked up manuscript.

In addition, we request that you upload any figures associated with your paper as individual TIF or EPS files with 300dpi resolution at resubmission; please read our figure guidelines for more information on our requirements: http://journals.plos.org/plosmedicine/s/figures. While revising your submission, please upload your figure files to the PACE digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at PLOSMedicine@plos.org.

We expect to receive your revised manuscript by May 08 2023 11:59PM. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

We ask every co-author listed on the manuscript to fill in a contributing author statement, making sure to declare all competing interests. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. If new competing interests are declared later in the revision process, this may also hold up the submission. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT. You can see our competing interests policy here: http://journals.plos.org/plosmedicine/s/competing-interests.

Please use the following link to submit the revised manuscript:

https://www.editorialmanager.com/pmedicine/

Your article can be found in the "Submissions Needing Revision" folder.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

We look forward to receiving your revised manuscript.

Sincerely,

Philippa Dodd MBBS MRCP PhD

PLOS Medicine

plosmedicine.org

-----------------------------------------------------------

Requests from the editors:

GENERAL

Please respond to all editor and reviewer comments detailed below, in full.

* Please revise your use of language when referring to both ‘migrants’ and ‘natives’, suggest instead native-born women and migrant women

** Please check carefully for the use of appropriate grammar, a number of minor errors negatively impacting reader accessibility were identified, including by the reviewers. We suggest inviting a native English speaker to proof read the manuscript prior to re-submission. Should the manuscript proceed successfully through the peer review process to publication, our copyeditors can help you further.

*** Please update your search to the present time. PLOS Medicine requires that all SR/MAs are updated to within 6 months of an anticipated publication date

COMMENTS FROM THE ACADEMIC EDITOR

I agree that this is an important area. However, as presented, the findings do not add a huge amount to the literature. In the main this is due to the simplistic comparison of migrant and native, as pointed out by Reviewer 4. .

It seems appropriate to challenge the authors to provide a major revision, including reanalyses as suggested by the statistical reviewer, and more nuanced discussion of the limitations as suggested by the other reviewers.

ABSTRACT

Thank you for reporting your abstract according to PRISMA for abstracts, following the PLOS Medicine abstract structure (Background, Methods and Findings, Conclusions)

We note reviewer #1 comments (below) and agree with the authors regarding combining the methods and findings section i-line with our formatting requirements.

Line 41 – please define RR and 95% CI at first use

Suggest the use of commas instead of hyphens (as these can be confused with reporting of negative values) to separate upper and lower bounds

PLOS Medicine requests that where 95% CIs are reported p values are also reported. Please report a p <0.001 or where higher as p=0.002, for example. Suggest formatting statistical information as follows, “…(pooled RR 1.36; 95%CI [1.13-1.64]; p</=)…”

Please include any important dependent variables that are adjusted for in the analyses

In the last sentence of the Abstract Methods and Findings section, please describe the main limitation(s) of the study's methodology.

Abstract Conclusions:

Please address the study implications without overreaching what can be concluded from the data; the phrase "In this study, we observed ..." may be useful.

Please interpret the study based on the results presented in the abstract, emphasizing what is new without overstating your conclusions.

Please avoid vague statements such as "these results have major implications for policy/clinical care". Mention only specific implications substantiated by the results.

When making your revision please ensure avoidance of any assertions of primacy

AUTHOR SUMMARY

At this stage, we ask that you include a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The author summary should consist of 2-3 succinct bullet points under each of the following headings:

• Why Was This Study Done? Authors should reflect on what was known about the topic before the research was published and why the research was needed.

• What Did the Researchers Do and Find? Authors should briefly describe the study design that was used and the study’s major findings. Do include the headline numbers from the study, such as the sample size and key findings.

• What Do These Findings Mean? Authors should reflect on the new knowledge generated by the research and the implications for practice, research, policy, or public health. Authors should also consider how the interpretation of the study’s findings may be affected by the study limitations.

The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract. Please see our author guidelines for more information: https://journals.plos.org/plosmedicine/s/revising-your-manuscript#loc-author-summary

METHODS and RESULTS

Please include details of how non-English language sources of studies were handled – see also methodological reviewer comments attached.

Could your study have searched databases more widely, would this have provided nay helpful additional information?

Line 167 – “…databases…” we agree with the methodological reviewer that seems rather an inappropriate description, suggest “…studies…”, as an alternative

As above, PLOS Medicine requests that where 95% CIs are reported p values are also reported. Please report a p <0.001 or where higher as p=0.002, for example. Please format statistical information as suggested above for the abstract.

Please replace the use of hyphens with commas to separate upper and lower bounds of 95% CIs

TABLES

Table 1 – please clarify/revise the use of the term vital statistics

FIGURES

Figure 1 – title: suggest “…study selection…”

As above, please ensure to revise figure titles to read “native-born”

Throughout, please indicate in the figure captions whether your analyses are adjusted or unadjusted. Where adjusted analyses are presented, please also include unadjusted analyses for comparison and clearly state the factors that are adjusted for.

Please also clearly indicate the meaning of the dots and lines in the figures. All captions should clearly report the figure content without the reader needing to refer to the manuscript text.

DISCUSSION

Please remove all sub-headings from the discussion such that the discussion reads as continuous prose.

Please present and organize the Discussion as follows: a short, clear summary of the article's findings; what the study adds to existing research and where and why the results may differ from previous research; strengths and limitations of the study; implications and next steps for research, clinical practice, and/or public policy; one-paragraph conclusion.

Line 230 – please avoid assertions of primacy which can be risky, suggest “…to our knowledge…”

REFERENCES

Please include an access date for web references

SUPPORTING INFORMATION

Please ensure that figure/table captions clearly define all content for the reader without the need to refer to the text

PRISMA checklist – thank you for including the PRISMA checklist, please amend and refer to section and paragraph numbers rather than page (or line) numbers as these often in the event of publication.

Table S3 – in context of transparent data reporting, the editorial team hugely appreciated the inclusion of this table but it is not a requirement.

Table S5 – please clarify/revise the use of the term vital statistics

Comments from the reviewers:

Reviewer #1: The authors address an important public health issue. It is nicely written, apart from the numerous unnecessary Oxford-commas. I would be interested to hear from the authors whether ´inequities` are not better than `inequalities`! I would separate `methods` from `findings´ in the abstract.

My main problem is with the definition of migrants as those who were not born in the host country. What then do we do with `women`who are born in the host countries`but with parents from the country of origin? Are they not migrants anymore?

That is different what we did with similar studies in the Netherlands. The definition also confused me in line 45, 282, 296 and 312 and that should be addressed in a revised version.

I agree with you that you cannot consider all migrants (called global migrants) as coming from the same background and consider them as coming from different regions is a helpful concept.

In abstract, line 50/51 it is unclear when you state `there is a need .... and to customize related health policies in each context.` Customized to what?

In line 51/52 you excluded maternal mental health problems from the review, but did not give an argument for that. It is, however, a frequent outcome of childbirth, and needs a reason for exclusion.

I did find in the figures one of our dutch papers being referenced as `Zwart and Van Hanegem`±I saw Zwart´s BJOG paper in the reference list but not the paper with Van Hanegem as the first autor (Acta Obstet Gynecol Scand).

Reviewer #2: See attachment

Michael Dewey

Reviewer #3: Overall, the study is well conducted and reported in a clear manner. I have the following comments for authors to address

1) Why did authors not used a method o describe the overall certainty of evidence such as GRADE methodology. Authors seems to focus on results of meta-analysis which is one piece of information and it needs to be considered with aspects of evidence such as type of study, risk of bias, heterogeneity of the evidence, indirectness and precision of summary estimates.

2) Why did authors not report an overall risk of maternal mortality in high income country irrespective of region in high income country?

3) Authors report that risk of maternal mortality is high in immigrant mothers in Europe based on RR 1.36 (1.13-1.64). This mean a relative increase risk of about 36 %. What is the absolute risk per 100, 000 or number need to harm? This is important as the absolute risk might be small as overall the maternal mortality is not a common event.

Reviewer #4: Dear authors,

Thank you for the opportunity to review this manuscript.

The manuscript offers important contributions to the field, as the research question is relevant to discussions regarding perinatal health disparities between migrants from different origins and non-migrants in different host countries. The meta-analyses are performed in line with current epidemiological standards and methods and findings are presented clearly.

However, I do believe that the research question and analysis are limited by the unidimensional comparison of foreign-born vs native-born women globally. Maternal mortality/morbidity is determined by complex interactions of a wide range of (social) determinants which need to be integrated in (intersectional) analyses to advance the current state of knowledge on this topic. Especially with regards to the Americas, comparing "native" to "foreign"born populations does not do justice to the colonial history, migration background of now 'native' populations etc. In line with this critique on the comparisons made, I believe that exclusion of studies before 1990 only has a very small impact on limiting heterogeneity in migrants' characteristics and integration policies.

Therefore, at least in the discussion of the findings, more attention needs to be given to the fact that comparing the umbrella term of migrants to the umbrella term of natives - without considering race/ethnicity of native groups as well, along with other determinants and their interactions - has only limited value to draw conclusions regarding the causal relationships between migration, ethnicity or any other variable and outcomes. For example, the authors could rephrase claims such as "the risk of severe maternal complications for mothers in the USA/Australia appears to be related more to race/ethnicity than to migration status". The authors should also be conscious of consistent use of all terms throughout the manuscript (for example, earlier in the paper they refer to "migration status" meaning "legal status", but in this specific statement migration status seems to refer to the fact that someone is a first-generation migrant).

With expanded critical reflections in the discussion of the findings, I believe the article to be of interest to clinicians and policymakers in the field of perinatal healthcare, as well as to researchers in the field of migration-related health inequities.

Other points of concern for minor revisions:

- In the presentation of the finding concerning differential risk of severe outcomes in women from different regions of origin, it is now unclear that this analysis was performed for studies both in USA and Europe. From the reading of the results, the reader could assume that this difference only concerns studies from Europe (given that no differences were found between migrants-natives in USA without taking country of birth into account).

- The manuscript is generally well-organized and written clearly enough to be accessible, although it would benefit from a thorough language check by a native English speaker given a number of (relatively minor) mistakes that cumulatively do compromise easy reading of the review.

Any attachments provided with reviews can be seen via the following link:

[LINK]

Attachment

Submitted filename: eslier.pdf

Click here for additional data file.^{(67.2KB, pdf)}

PLoS Med. 2023 Jun 22;20(6):e1004257. doi: 10.1371/journal.pmed.1004257.r003

Author response to Decision Letter 1

8 May 2023

Attachment

Submitted filename: Eslier_Answers to reviewers_R2.docx

Click here for additional data file.^{(647.3KB, docx)}

PLoS Med. doi: 10.1371/journal.pmed.1004257.r004

Decision Letter 2

Philippa Dodd

26 May 2023

Dear Dr. ESLIER,

Thank you very much for re-submitting your manuscript "Association between migration and severe maternal outcomes in high income countries: systematic review and meta-analysis" (PMEDICINE-D-22-03069R2) for review by PLOS Medicine.

I have discussed the paper with my colleagues and the academic editor and it was also seen again by 3 reviewers. I am pleased to say that provided the remaining editorial and production issues are dealt with we are planning to accept the paper for publication in the journal.

The remaining issues that need to be addressed are listed at the end of this email. Any accompanying reviewer attachments can be seen via the link below. Please take these into account before resubmitting your manuscript:

[LINK]

In revising the manuscript for further consideration here, please ensure you address the specific points made by each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file.

Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. If you haven't already, we ask that you provide a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract.

We expect to receive your revised manuscript within 1 week. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

We ask every co-author listed on the manuscript to fill in a contributing author statement. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT.

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.

Please note, when your manuscript is accepted, an uncorrected proof of your manuscript will be published online ahead of the final version, unless you've already opted out via the online submission form. If, for any reason, you do not want an earlier version of your manuscript published online or are unsure if you have already indicated as such, please let the journal staff know immediately at plosmedicine@plos.org.

If you have any questions in the meantime, please contact me or the journal staff on plosmedicine@plos.org.

We look forward to receiving the revised manuscript by Jun 02 2023 11:59PM.

Sincerely,

Philippa Dodd, MBBS MRCP PhD

PLOS Medicine

plosmedicine.org

------------------------------------------------------------

Requests from Editors:

GENERAL

Thank you for your detailed and considered responses to previous editor and reviewer requests. Please see below for further comments which we require you address prior to publication.

Comments from the Editor-in-chief: The finding of no difference in outcomes in the US (or Australia) is interesting and surprising. How different is the benchmark across these countries i.e. are maternal outcomes for native-born women worse in the US (and/or Australia) compared to outcomes for native-born women in Europe, for example? Please consider how the results are framed/compared in this context.

ABSTRACT and AUTHOR SUMMARY

It would be helpful to indicate that the studies included were conducted at a national level.

AUTHOR SUMMARY

Line 84 – ‘This result provides insight valuable for further exploring these inequalities’ mechanisms.’ Suggest instead, ‘These data highlight the need to further explore the mechanisms underlying these inequities.’ Or similar

Line 86 – the latter part of this statement is rather vague ‘…take into account the multiple dimensions of the women’s social context’ please revise.

TABLES

Table S3 – please feel free to include this table with the manuscript as supporting information.

REFERENCES

Ref 38 line 523 – what does the asterisk represent here? Can it be removed?

Ref 67 line 608 – what to the 3 stars represent here? Can they be removed?

SOCIAL MEDIA

If not already done so, to help us extend the reach of your research, please detail any Twitter handles you wish to be included when we tweet this paper (including your own, your co-authors’, your institution, funder, or lab) in the manuscript submission form when you re-submit the manuscript.

Comments from Reviewers:

Reviewer #1: The authors have undertaken a huge job to review all the literature in relation to migration and maternal health and bring together these data in a nice review. There is only one issue I still have, because my earlier question was not answered. I have very well understood their defintion of migrant and native women. The Dutch data, however, are still a bit different, because in our papers a woman born in the Netherlands but with one or two parents born in Marocco is still considered as a migrant woman. Only in the paper about asylumseekers the migrants cannot be born in the Netherlands, so they all confirm with the definition used in the paper. I cannot assess this issue for the other studies. But I would suggest to include this as a limitation, at least for our dutch studies. Jos van Roosmalen

Reviewer #2: The authors have addressed all my points but there is one minor issue remaining.

I suggested performing a meta-regression using both host country and birth region as moderators. I did not find the response very convincing. They will no doubt be related, that is the point, but I do not see that the analysis is necessarily fatally flawed a priori. I would suggest trying it and seeing what happens or at least expand the limitations section to indicate that the relationship with host country and the relationship with birth region may be saying the same thing twice.

Michael Dewey

Reviewer #4: Dear authors,

It was a pleasure to review your revised manuscript. I believe you improved the manuscript substantially based on all reviewers' comments. The results are more meaningful and the discussion offers more depth and critical reflection now. I think the manuscript is now acceptable for publication, although I still think the quality and clarity of the writing could be improved in some instances, e.g. line 273 "Our systematic review shows that (...), while women in the USA and Australia did not." should be "while MIGRANT women in the USA and Australia did not".

Best regards

Any attachments provided with reviews can be seen via the following link:

[LINK]

PLoS Med. 2023 Jun 22;20(6):e1004257. doi: 10.1371/journal.pmed.1004257.r005

Author response to Decision Letter 2

3 Jun 2023

Attachment

Submitted filename: Eslier_Answers to reviewers_R3.docx

Click here for additional data file.^{(40.8KB, docx)}

PLoS Med. doi: 10.1371/journal.pmed.1004257.r006

Decision Letter 3

Philippa Dodd

5 Jun 2023

Dear Dr ESLIER,

On behalf of my colleagues and the Academic Editor, Dr. Sarah Stock, I am pleased to inform you that we have agreed to publish your manuscript "Association between migration and severe maternal outcomes in high income countries: systematic review and meta-analysis" (PMEDICINE-D-22-03069R3) in PLOS Medicine.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. Please be aware that it may take several days for you to receive this email; during this time no action is required by you. Once you have received these formatting requests, please note that your manuscript will not be scheduled for publication until you have made the required changes.

In the meantime, please log into Editorial Manager at http://www.editorialmanager.com/pmedicine/, click the "Update My Information" link at the top of the page, and update your user information to ensure an efficient production process.

PRESS

We frequently collaborate with press offices. If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximise its impact. If the press office is planning to promote your findings, we would be grateful if they could coordinate with medicinepress@plos.org. If you have not yet opted out of the early version process, we ask that you notify us immediately of any press plans so that we may do so on your behalf.

We also ask that you take this opportunity to read our Embargo Policy regarding the discussion, promotion and media coverage of work that is yet to be published by PLOS. As your manuscript is not yet published, it is bound by the conditions of our Embargo Policy. Please be aware that this policy is in place both to ensure that any press coverage of your article is fully substantiated and to provide a direct link between such coverage and the published work. For full details of our Embargo Policy, please visit http://www.plos.org/about/media-inquiries/embargo-policy/.

Thank you again for submitting to PLOS Medicine. We look forward to publishing your paper.

Best wishes,

Pippa

Philippa Dodd, MBBS MRCP PhD

PLOS Medicine

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Table. Literature search algorithm on Medline via PubMed.

(DOCX)

Click here for additional data file.^{(12.9KB, docx)}

S2 Table. Literature search algorithm on Embase.

(DOCX)

Click here for additional data file.^{(12.9KB, docx)}

S3 Table. Literature search algorithm on Cochrane Library.

(DOCX)

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S4 Table. List of the excluded studies and reasons for their exclusion.

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S5 Table. Characteristics of the included papers, listed in alphabetical order of first authors.

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S6 Table. Methodological quality of the studies included (listed in alphabetical order) assessed with the Newcastle–Ottawa Scale (NOS).

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S7 Table. Amendments made to the protocol PROSPERO.

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S1 Fig. Maternal mortality in migrant women and native-born women.

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S2 Fig. All-cause severe maternal morbidity in migrant women and native-born women.

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S3 Fig. Maternal intensive care unit admission in migrant women and native-born women, stratified by host country.

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S4 Fig. Maternal intensive care unit admission in migrant women and native-born women stratified by migrant women’s region of birth.

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S5 Fig. Funnel plot for studies reporting maternal mortality overall.

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S6 Fig. Funnel plot for studies reporting maternal mortality stratified by host country.

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Attachment

Submitted filename: eslier.pdf

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Attachment

Submitted filename: Eslier_Answers to reviewers_R2.docx

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Attachment

Submitted filename: Eslier_Answers to reviewers_R3.docx

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Data Availability Statement

All relevant data are within the manuscript and its Supporting Information files.

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PERMALINK

Association between migration and severe maternal outcomes in high-income countries: Systematic review and meta-analysis

Maxime Eslier

Elie Azria

Konstantinos Chatzistergiou

Zelda Stewart

Agnès Dechartres

Catherine Deneux-Tharaux

Roles

Abstract

Background

Methods and findings

Conclusions

Trial Registration

Summary

Why was this study done?

What did the researchers do and find?

What do these findings mean?

Introduction

Methods

Search strategy and selection criteria

Data analysis

Results

Characteristics and methodological quality assessment

Fig 1. Study selection.

Table 1. Characteristics of included studies.

Maternal mortality

Fig 2. Maternal mortality in migrant women and native-born women, stratified by host country.

Fig 3. Maternal mortality in migrant women and native-born women, stratified by migrant women’s region of birth.

All-cause severe maternal morbidity

Fig 4. All-cause severe maternal morbidity in migrant women and native-born women, stratified by host country.

Fig 5. All-cause severe maternal morbidity in migrant women and native-born women, stratified by migrant women’s region of birth.

Cause-specific severe maternal morbidity

Fig 6. Maternal ICU admission in migrant women and native-born women.

Fig 11. Uterine rupture in migrant women and native-born women.

Fig 7. Near misses in migrant women and native-born women.

Fig 8. Eclampsia in migrant women and native-born women.

Fig 9. Severe postpartum hemorrhage in migrant women and native-born women.

Fig 10. Severe sepsis in migrant women and native-born women.

Discussion

Supporting information

Acknowledgments

Abbreviations

Data Availability

Funding Statement

References

Decision Letter 0

Beryne Odeny

Roles

Decision Letter 1

Philippa Dodd

Roles

Author response to Decision Letter 1

Decision Letter 2

Philippa Dodd

Roles

Author response to Decision Letter 2

Decision Letter 3

Philippa Dodd

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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