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. 2023 Oct 19;25:101532. doi: 10.1016/j.ssmph.2023.101532

Increased number of live births by migrant mothers shows areal inequality in Japan: A descriptive study

Kimihiro Nishino 1,∗, Souphalak Inthaphatha 1, Eiko Yamamoto 1
PMCID: PMC10958628  PMID: 38524177

Abstract

Japan has not implemented policy of accepting many migrants, and the proportion of migrants in the total population is much smaller than that in other economically developed countries. Therefore, issues regarding the health status of migrants, especially migrant mothers and their children, have not been discussed enthusiastically in Japan. In the present study, we aimed to describe trends and spatial patterns (time trend of the number, areal distribution, and frequency of maternal nationality of newborn births) of live births by migrant mothers in Japan, which contributes to the administration of medical policies on the perinatal care of migrant mothers. This study used data from the vital statistics reported by the Ministry of Health, Labour and Welfare (MHLW) of Japan and from foreign resident statistics reported by Immigration Services Agency (ISA) of Japan. To show areal inequality in the number of live births by migrant mothers, we applied the Gini coefficient. This study demonstrated that the number of live births by migrant mothers increased from 16,154 (1.31% of the total) in 1990 to 26,517 (3.08%) in 2020. It also showed stronger areal inequality at prefecture level by Japanese mothers (Gini coefficient; 0.64 vs 0.46 in 2020), and this areal inequality has increased during the last decade. This study also illustrated that the frequency of maternal nationality of newborns from migrant mothers has been altered in the last decade, especially in the composition of Asian countries. In conclusion, the number of live births by migrant mothers in Japan has been progressively increasing; however, this trend is excessively concentrated in specific areas in Japan. These tendencies are expected to become more prominent in the future, and their possible impacts on medical institutions and administrative agencies in specific areas that treat migrant mothers should be investigated and discussed.

1. Introduction

According to a report by the United Nations Department of Economic and Social Affairs, the number of international migrants living outside their countries of origin reached 281 million in 2020. This number increased from 173 million in 2000 and 221 million in 2010, accounting for 3.6% of the global population in 2020 (International migration, 2022). Female migrants constitute half of all international migrants, and many pregnant migrants are forced to deliver outside their country of birth or citizenship. Pregnancy through different lifestyles under the circumstances of different nationalities, languages, cultures, religions, and economic states from original ones can be stressful or burdensome to pregnant migrants. Indeed, it has been reported that migrant women have a higher risk of adverse perinatal outcomes such as preterm delivery, low birth weight, lower Apgar scores, still birth, placental abruption, and gestational diabetes mellitus, than non-migrant women (Garnica-Rosas et al., 2021; Juárez & Hjern, 2017; Maeland et al., 2021; Strandberg et al., 2021; Törn et al., 2021; Urquia et al., 2015; Vik et al., 2019; Vik et al., 2020).

Japan has not implemented a policy of accepting a large number of migrants, and the proportion of migrants to the total population is much smaller than in other economically developed countries, such as the United States and many European countries (International migration, 2022). Therefore, issues regarding the health status of migrants and their medical and welfare administration have not been enthusiastically discussed in Japan, particularly regarding migrant mothers and their children. Basic statistics for the administration of medical policies on perinatal care of migrant mothers, such as the number and geographic distribution of live births by migrant mothers and the frequency of maternal nationality of newborn babies, have not been highlighted.

This study aimed to describe the trends and spatial patterns (time trend of the number, areal distribution, and frequency of maternal nationality of newborns) of live births by migrant mothers in Japan, which contributes to administer medical policies on perinatal care of migrant mothers.

2. Materials and methods

2.1. Study design and data sources

This was a descriptive, data-linkage study on live births among migrant mothers in Japan. We retrieved and processed data on the number of live births by both Japanese and migrant mothers from the vital statistics which are annually reported by Ministry of Health, Labour and Welfare (MHLW) of Japan (Vital statistics, 2022) and data on the number of resident migrants including two sexes and all generations in Japan from Foreign resident statistics which are reported by Immigration Services Agency (ISA) of Japan twice a year (we adopted ‘End of December’ version for each year in this article) (Foreign resident statistics, 2022). In these reports, migrants in Japan are defined as mid-to long-term (equal to or more than three months) residents under certification by the Immigration Control and Refugee Recognition Act and special permanent residents specified by the Special Act on Immigration Control (Foreign resident statistics, 2022). Regardless of their nationality and type of certification, migrant mothers in Japan are all provided with the right to be given the same political services and support for giving birth and raising their children as Japanese mothers after notification of pregnancy and obtaining a Maternal and Child Health Handbook. Migrant mothers can freely access places where they give birth, and they can receive medical care and services at any institution when they get sick, because all migrants in Japan are obliged to receive medical insurance as well as the Japanese. Birth certificates of their children including parents' nationality must be submitted to local municipal offices within 2 weeks of delivery to receive various public services for upbringing their children; therefore, almost all live births in Japan are considered to be registered. Birth certificates were summarized at the local municipal offices and the collected data were sent to the MHLW office and reported as vital statistics. The use of these data, which were open to the public by the Japanese government, was approved without ethical review (Vital statistics, 2022).

2.2. Geographic distribution of the number of live births by migrant mothers and residency of migrants in Japan

We grouped each prefecture (total: 47) in Japan into five groups based on the number of live births by migrant mothers (from 2020/01/01 to 2020/12/31) to describe the geographic distribution: (i) 0–999, (ii) 1000–1,999, (iii) 2000–2,999, (iv) 3000–3,999, and (v) 4000 or more. Similarly, we classified each prefecture based on the number of migrants’ residencies at the end of December 2020 into five groups: (i) 0–99,999, (ii) 100,000–199,999, (iii) 200,000–299,999, (iv) 300,000–399,999, and (v) 400,000 or more.

2.3. Areal inequality on the number of live births and residency in Japan (The Gini coefficient)

The Gini coefficient, showing areal inequality according to the number of live births by migrant mothers at the prefectural level, was calculated for each year from 2010 to 2020 as follows: First, we created a frequency table composed of ten classes that counted the number of prefectures (total: 47), where the number of live births by migrant mothers was within the range (each class had a range of 500 as the number: minimum: 0–499 and maximum: 4500–4999). Second, we calculated the relative and cumulative relative frequency of each class, and using the total number of live births by migrant mothers of each class and the total sum, we calculated the relative and cumulative relative values of each class. Third, we drew a Lorenz curve (Moskowitz et al., 2008) in which the cumulative relative frequency of each class served as horizontal axis and cumulative relative value of each class as vertical axis, with a line of perfect equality. Finally, we measured the Gini coefficient by multiplying the area surrounded by the Lorenz curve and the line of perfect equality by two as described elsewhere (Moskowitz et al., 2008). Corresponding procedures were performed for the number of live births by Japanese mothers and the residency of migrants and the Japanese (each with 10 classes).

2.4. Maternal nationality of newborns in Japan

We collected data on maternal nationality of newborns born to migrant mothers between 2010 and 2020 and divided them into nine groups: (north and south) Korea, China, the Philippines, Thailand, the United States (U.S), the United Kingdom (U.K), Brazil, Peru, and “other countries”. This was because countries other than former eight were lumped together as “other countries” at the stage of local municipal offices where birth certificate of newborns born to migrant mothers were to be submitted with parents’ nationalities and MHLW report nine groups of maternal nationalities as they were collected. To compare the frequency of maternal nationalities of newborns born to migrant mothers, we applied the same grouping method to resident migrants, although the ISA reported all nationalities of resident migrants in Japan.

2.5. Statistical analysis

JMP PRO version 15.1.0 (SAS Institute, Inc., Cary, USA) was used for statistical analysis.

3. Result

3.1. The proportion of live births by migrant mothers in Japan has progressively increased over the past 30 years

Trends in the total number of live births in Japan and the proportion of live births by migrant mothers to total in Japan between 1990 and 2020 are shown in Fig. 1A. While the number of live births by Japanese mothers, which accounts for the greatest proportion of the total births in Japan, drastically decreased from 1,212,890 in 1990 to 83,115 in 2020, and the number of migrant mothers has increased from 16,154 in 1990 to 26,517 in 2020, resulting in a progressive increase in the proportion of migrant mothers in Japan from 1.31% to 3.08% over the past 30 years. The proportion of live births among migrant mothers whose partners were not Japanese increased from 46.2% in 1990 to 70.9% in 2020 (Fig. 1B). This trend corresponded to the number of resident migrants (Fig. 1C).

Fig. 1.

Fig. 1

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(A) Trends in the total number of live births in Japan and the proportion of live births by migrant mothers to total in Japan between 1990 and 2020. (B) Trends in the number of live births by migrant mothers whose partners are Japanese (gray bars) and non-Japanese (black bars) in Japan between 1990 and 2020. (C) Trends in the number of resident migrants in Japan between 1990 and 2020. Data for 1991 and 1993 are missing.

3.2. The number of live births by migrant mothers showed stronger areal inequality than that of Japanese mothers

Fig. 2A shows the areal distribution based on the number of live births of migrant mothers in Japan in 2020. Live births by migrant mothers were concentrated in four prefectures: Tokyo, Aichi, Kanagawa, and Osaka, where representative metropolitan cities exist, whereas the number of live births in other prefectures was mostly less than 1000. The Gini coefficient that showed areal inequality at prefecture level in the number of live births by migrant and Japanese mothers was shown in Fig. 2B. The former was considerably higher than the latter in 2020 (0.64 vs 0.46, Fig. 2B). This figure illustrates that areal inequality in the number of live births by migrant mothers has accelerated, and the discrepancy between these values by migrant and Japanese mothers has increased during the last decade. To investigate these trends, we performed similar analyses on the numbers of resident migrants in Japan and Japanese residents. As illustrated in Fig. 2C, the areal distribution of resident migrants in 2020 was polarized in the four prefectures, where the number of live births by migrant mothers was prominent. The Gini coefficient showing areal inequality at prefecture level on the number of resident migrants was relatively higher than counterpart and the difference between them was expanded through this period (Fig. 2D).

Fig. 2.

Fig. 2

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(A) Areal distribution based on the number of live births of migrant mothers in Japan in 2020. (B) Trends in the Gini coefficient showing areal inequality at the prefecture level on the number of live births by migrant and Japanese mothers between 2010 and 2020. (C) Areal distribution based on the number of resident migrants in Japan in 2020. (D) Trends in the Gini coefficient showing areal inequality at the prefecture level in the number of resident migrants and Japanese between 2010 and 2020.

3.3. The frequency of maternal nationality of newborns born to migrant mothers from Asian countries, excluding Korea, China, the Philippines, and Thailand, is expected to have substantially increased in the last decade

The changes in the frequency of maternal nationality of newborns born to migrant mothers from 2010 to 2020 are shown in Fig. 3A. The proportions of Korea, China, the Philippines, Thailand, Brazil, and Peru have decreased, those of the U.S and the U.K, have been stable, and that of “other countries” has increased. Unfortunately, we could not obtain detailed information about “other countries”, as described in the Materials and Methods. However, we could estimate the component of “other countries” in maternal nationality of newborns born to migrant mothers because the composition and trend of maternal nationality were similar to those of nationality of resident migrants (Fig. 3A and B). When we investigated the component of “other countries” in nationality of resident migrants from Foreign resident statistics, Asian countries excluding Korea, China, the Philippines, and Thailand had occupied the greatest part in “other countries” and they have progressed from 63.7% of “other countries” in 2010 to 86.9% in 2020 (Fig. 3B, squares with dotted lines). Therefore, it is suggested that the big expansion of “other countries” in the last decade in proportion of maternal nationality of newborns born to migrant mothers might be due to increased number of live births by mothers from Asian countries excluding these four counties such as Vietnam, Nepal and Indonesia. For instance, Vietnam is supposed to have a major part in “other countries” in 2020 in maternal nationality because it has developed in proportion to the nationality of resident migrants from 1.95% of the total in 2010 to 15.5% in 2020. If “other countries” in maternal nationality in 2010 and 2020 were constituted of countries as the same proportion of those in resident migrants in the respective year, Asian countries excluding Korea, China, the Philippines, and Thailand would occupy from 10.4% of total in 2010 and up to 32.7% in 2020. This means all Asian countries occupy from 79.7% of total in 2010 and up to 83.6% in 2020.

Fig. 3.

Fig. 3

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The frequency of maternal nationality of newborn born to migrant mothers in 2010 and 2020 (A) and nationality of resident migrants in 2010 and 2020 (B). #; North and South Korea. Squares with dotted lines indicate Asian countries, excluding Korea, China, Philippines, and Thailand.

4. Discussion

In the present study, we demonstrated that the number of live births by migrant mothers has increased over the last 30 years, whereas the total number of live births in Japan has constantly decreased, resulting in a progressive increase in the proportion of migrant mothers in Japan. Additionally, we clarified that the number of live births by migrant mothers showed stronger areal inequality at the prefecture level than that by Japanese mothers, and that this areal inequality has accelerated each year over the last decade. Finally, we found that the frequency of maternal nationality of newborns born to migrant mothers from Asian countries including Korea, China, the Philippines, and Thailand has decreased, while that from Asian countries excluding these four countries is expected to have substantially increased in the last decade.

The number of live births by Japanese mothers has drastically decreased in recent 30 years, greatly due to the decreased number of marriage and the increased number of unmarried and late-married women as well as other developed countries. These changes have been brought by various alternations in lifestyles and economic status among Japanese women (Ghaznavi et al., 2022). Meanwhile, the number of live births by migrant mothers has increased in the same period (Fig. 1A and B). This is greatly contributed by the increase in the number of resident migrants as supported by the increased number of live births by migrant mothers whose husbands are not Japanese (Fig. 1B and C). The increased influx of migrants into Japan has been rapidly promoted according to the progressive globalization seen as the increased number of workers, interns and students from overseas, especially from Asian countries (Fig. 3B). However, the number of resident migrants and also live births by migrant mothers has not constantly increased over the past 30 years; instead, it has declined across several years after 1998 and 2008. They were when Asian and global financial crises occurred, and Japanese (and the world) economics worsened substantially. They illustrated that the stagnated economics of the host country affected the dynamics and reproductive actions of migrants (Tilly, 2011), although there should have been other factors that have driven migrant minds.

Live births by migrant mothers are more unevenly distributed in specific prefectures in Japan, where metropolitan cities exist, than those by Japanese mothers, and this tendency has accelerated over the last decade, reflecting a similar situation for resident migrants (Fig. 2A, B, C, and D). The accumulation of resident migrants in metropolitan cities is perhaps because of the following reasons that are characteristic of metropolitan cities that attract migrants. Many companies and educational institutions accept many migrant residents, wages are relatively higher than in smaller cities, and localized communities consisting of pre-settled migrants have already been established (Igarashi, 2022; Tanis, 2020; Wimark et al., 2019). The existence of localized communities can provide significant relief and encouragement for migrant women who think of being pregnant and who might face linguistic barriers and unfamiliar cultures under social isolation to give birth and raise their children (Peláez et al., 2017; Soltani et al., 2020). Some countries and metropolitan cities also have strong integration policies and provide various supportive services around migrant lives including access to information, language, residency, medical care/welfare, employment and so on, which attract migrants (Juárez et al., 2019). Although Japan has not implemented strong integration policies, it is clear from the trend that the excessive concentration of live births by migrant mothers in specific prefectures in Japan will become more prominent in the future. On the other hand, the accumulation of resident migrants in specific metropolitan cities can be burden because the potential risk of a pandemic should be increased. Moreover, pregnancy outcome of migrant mothers are worse than that of non-migrant mothers, which can be burden in host cities as well (Bollini et al., 2009). The possible impact on medical institutions and administrative agencies in specific areas in Japan that treat migrant mothers should be investigated and discussed.

It is a critical problem to immediately resolve that precise statistics of nationalities of all migrant mothers who have given birth in Japan cannot be obtained by government databases (Fig. 3A) because data on the nationalities of migrant mothers and languages are fundamental to formulate and administer policies on perinatal care concerned with migrant mothers and their children. In particular, many Asian countries with growing populations (Fig. 3B) use their own minority languages; therefore, understanding the exact frequency of nationalities of migrant mothers in Japan is essential to realize open and empathetic medical care and services.

The present study has some limitations. First, this study is based on the number of live births, including multiple pregnancies recorded in a national database, and not on the number of migrant or Japanese mothers themselves who might have experienced single/multiple time(s) of birth, or live/still birth(s). Second, situations after COVID-19 pandemic were not evaluated at the time of description of this study. The COVID-19 pandemic has impacted social, economic, and medical situations worldwide. Therefore, changes in migrant mothers’ attitudes due to the COVID-19 pandemic should be evaluated in the future. Couples of migrant fathers and Japanese mothers were not considered in this study because the main role of perinatal care is played by mothers, rather than fathers, although there might be some challenges to be addressed in this setting.

5. Conclusion

The number of live births among migrant mothers has increased. However, it is excessively concentrated in prefectures where metropolitan cities exist. The frequency of maternal nationality of newborns born to migrant mothers has dramatically altered in the last decade, especially in Asian countries. Our descriptive investigation of live births by migrant mothers, which has been expanding progressively, has unearthed the necessity of exploring whether the potential unmet needs of migrant mothers exist and whether administrative agencies and medical facilities in Japan supply sufficient services to satisfy them.

Ethical approval and consent to participate

No concerns regarding ethical approval and consent to participate exist in this article, as mentioned in the Materials and Methods section.

Funding

None.

Disclosure of interest

The authors declare that they have no conflicts of interest.

List of Abbreviations and Acronyms

MHLW

Ministry of Health, Labour and Welfare

ISA

Immigration Services Agency

U.S

United States

U.K

United Kingdom

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