The sequelae of the COVID-19 pandemic on maternal body mass index, gestational weight gain, and delivery-associated birth complications: a nationwide epidemiologic study

Abstract

Background

Evidence as to whether COVID-19-mitigating measures affected the metabolic status of pregnant women is lacking. This is the first study to analyze changes in pre-pregnancy weight, body mass index (BMI), gestational weight gain (GWG), the prevalence of overweight and obese women conceiving, and delivery-associated complications during the COVID-19 pandemic compared to pre-pandemic times.

Methods

This nationwide cohort study analyzed birth registry data from all obstetric departments in Austria. The period from 05 to 12/2020 was defined as the pandemic period (N = 30,806), whereas the period from 05–12/2015–2019 was defined as the pre-pandemic period (N = 162,463).

Results

The pre-pregnancy weight and BMI were 64 (57–73) kg and 23.03 (20.70–26.37) kg/m² during the COVID-19 pandemic versus 63 (56–72) kg and 22.7 (20.57–22.77) kg/m² during the pre-pandemic period (p < 0.001). The GWG remained constant at 13 kg and 4.8 kg/m² between the exposure and control periods (p = 0.69; p = 0.65). A multivariate analysis revealed that the COVID-19 pandemic had a significant impact on pre-pregnancy weight (OR 1.01; 95% CI 1.00-1.02; p < 0.001) after adjusting for covariates (age, height, parity). During the COVID-19 pandemic period, a significantly higher percentage of women with overweight and obesity class I-III were reported compared to pre-pandemic times (p = 0.003, p < 0.001, p< 0.001). Finally, both more macrosomic infants (p = 0.003) and vacuum-assisted deliveries (p = 0.020) occurred during the COVID-19 pandemic.

Conclusions

COVID-19-mitigating measures worsened the metabolic status of pregnant women. To counteract this, targeted intervention programs must be implemented immediately as an integral part of the pandemic recovery plan.

Introduction

On March, 11th 2020, the World Health Organization (WHO) declared the coronavirus (COVID-19) outbreak, which emerged in Wuhan, China in December 2019, to be a global pandemic. Now, more than three years later, humanity is facing an appalling pandemic dashboard. To date, 765,903,278 confirmed cases, almost 7 million deaths, and at least 65 million individuals with long COVID have been reported worldwide [1]. Due to the increasing immunity conferred by the large number of people who have had the disease, combined with the administration of vaccines and effective treatments, countries worldwide have succeeded in repealing COVID-19 regulations. Tedros Adhanom Ghebreyesus, the general director of the WHO, officially ended the most devastating pandemic of the 21st century on May 5th, 2023.

Although the acute crisis seems to be over, the sequelae of COVID-19 will perpetuate in several public health areas. To control the rapid transmission of the virus, countries enforced strict measures, such as the reduction of interpersonal contact, stay-at-home orders, and lockdowns and/or self-quarantine [2]. These virus-mitigating measures led to dramatic changes in lifestyle, including significant alterations in physical activity levels, dietary habits, sleep patterns, and stress levels [3–5]. Specifically, researchers have reported an increase in the number of sedentary hours and a lack of adequate daily exercise, combined with elevated caloric intakes, more regular snacking, increased processed food and alcohol consumption, and decreased fresh fruit and vegetable consumption [6–11]. Furthermore, researchers have identified a reduction in sleep quality in conjunction with an increase in sleep disturbances, insomnia, and sleep medication consumption. Negative emotions (e.g., depression, anxiety, and stress) also increased during the pandemic [4, 12, 13]. Pandemic policy measures also impacted social determinants of health, including income and job loss, thereby disproportionately affecting low-income and marginalized populations worldwide [14, 15].

As physical inactivity, poor diet, stress, and low socioeconomic status are all known risk factors for overweight, it is not surprising that a body of literature highlights that the COVID-19 crisis has dramatically increased weight and body mass index (BMI), as well as the prevalence of obesity in a substantial part of the population of all age groups, especially in the middle and high income countries [7, 14, 16–21]. A systematic review and meta-analysis of Anderson et al. (2023) reported a difference of 0.93 kg for weight and 0.38 kg/m² for BMI, and a 1% increase in the prevalence of obesity in adults between pandemic and pre-pandemic periods [22]. Notably, in children the difference was 1.65 kg for weight and 0.13 for BMI z-scores; and the prevalence of obesity increased by 2% in dependence to the COVID-19 period [22].

Evidence regarding whether the pandemic had an effect on the weight and BMI among pregnant women is still emerging, as most studies to date have focused on the impact of COVID-19 on gestational weight gain (GWG) alone or on the risk of developing gestational diabetes [23, 24]. Obesity in pregnancy is associated with both maternal and neonatal morbidity and mortality, as well as serious long-term consequences for the infant [25–28]. Therefore, a detailed analysis of whether the pandemic altered the metabolic status of pregnant women is highly warranted. This large, nationwide cohort analysis aims to comprehensively evaluate anthropometric parameters—pre-pregnancy weight, changes in BMI, and gestational weight gain—in relation to the prevalence of maternal obesity and delivery-associated complications during the COVID-19 pandemic, compared with pre-pandemic periods.

Methods

Study design and participants

This study was reported according to the STROBE guidelines for observational studies. It is a nationwide retrospective cohort study analyzed data from the Austrian birth registry- a prospective, population-based database comprising information on deliveries from all obstetric departments in the country. Comprehensive information on both maternal characteristics and perinatal outcomes is included in this registry. Data collection from all hospitals occurs quarterly to ensure adequate data control and quality. The period from May 1 and December 31, 2020 was defined as the COVID-19 period, and the women who delivered during this period were considered eligible for the pandemic group (N = 30,806). In contrast, the cumulative period from May 1 to December 31 of 2015 to 2019 was defined as the pre-pandemic period (N = 162,463). Assignment to one of the study groups was not associated with an individual’s COVID-19 status, which remained unknown for both groups. Because of their potential effect on the outcomes, only women who had live births ≥ 37 + 0 weeks of gestation were included. Cases with multiple birth, fetal malformations, chromosomal aberrations, and cases with inconclusive or missing data were excluded from the analyses. Characteristics assessed in both the study and control groups included maternal age, parity, gestational age, and neonatal short-term outcomes. Offspring sex was included as a standard neonatal characteristic and as a potential biological modifier, given that fetal growth patterns and birth outcomes are known to differ by sex [25].

Pre-pregnancy weight and BMI

To assess the primary outcome parameters, pre-pregnancy weight (kg), as recorded in the Austrian birth registry, was used. Pre-pregnancy weight was self-reported and refers to maternal weight immediately prior to conception, as documented in the Austrian Mother–Child Health Passport. The calculation of pre-pregnancy BMI was done using the formula weight in kilograms (kg) divided by the height in meters squared (m²). BMI estimates of body fat in non-pregnant women explained 50–70% of the variance in fat mass. During pregnancy, the significant increase in total body water makes the correlation less robust [29]. Therefore, it is not valid to use BMI to classify obesity during pregnancy [27]. Therefore, in our study, BMI was used solely to measure the metabolic status of the women during the pre-pregnancy period, whereas GWG was used to determine their metabolic status during pregnancy.

Secondary outcome parameters

GWG was defined as weight at term minus self-reported weight at the beginning of pregnancy. It is a valid parameter for stratifying the risk for both adverse short- and long-term outcomes of mothers and infants [30]. To evaluate the prevalence of overweight and obese women between the pandemic and pre-pandemic periods, BMI categorization according to the guidelines of the WHO was conducted as follows [31]: underweight, < 18.5 kg/m²; normal weight, 18.5–24.9 kg/m²; overweight, 25.0–29.9 kg/m²; obesity class I, 30.0–34.9 kg/m²; class II, 35.0–39.9 kg/m²; and class III, ≥ 40 kg/m². According to the most widely used guidelines developed by the Institute of Medicine, the recommended GWG for women with underweight, normal weight, overweight, and morbid obesity (all classes) pre-pregnancy is 12.5–18.0 kg, 11.5–16.0 kg, 7.0–11.5 kg, and 5.0–9.0 kg, respectively [32, 33]. Delivery-associated complications previously identified in the literature as being associated with maternal overweight and obesity were assessed, including fetal macrosomia (birth weight ≥ 4 kg), vacuum delivery, higher-grade perineal lacerations, episiotomy, shoulder dystocia, and non-elective cesarean Sect. [25].

Statistical analyses

Statistical analyses were performed using Stata software version 13 (StataCorp LLC, College Station, TX, USA). All hypotheses were examined at a significance level of 0.05 with a two-sided alternative. Descriptive statistics were determined for baseline maternal and neonatal characteristics, as well as primary and secondary outcome measures. Continuous variables were calculated as median with a minimum and maximum. Categorical variables were calculated using absolute and relative frequencies. Differences in the parameters between the exposure and control periods were assessed using Mann-Whitney U tests or chi-squared tests. To determine whether the COVID-19 period was a potential risk factor contributing independently to increase in pre-pregnancy weight, a multivariate logistic regression model was applied. First, with a forward variable selection strategy, we used the likelihood ratio to test whether the a priori-selected covariates yielded a statistically significant contribution to the model. For the second model, we used a backward strategy for variable selection. Based on the available literature, we included the following covariates in the model: maternal age, parity, and height [27, 34]. Univariate and multivariate adjusted odds ratios (OR) with 95% CIs were calculated for each risk factor.

Results

Study population

In total, 511,384 deliveries were recorded during the entire study period, of which 510,342 cases were eligible for analysis. Of these, 284,187 fulfilled the inclusion criteria, and 90,918 cases were excluded due to delivery between January and April. This led to a COVID-19 pandemic period group of 30,806 cases and a pre-pandemic period group of 162,463 cases. The inclusion and exclusion criteria for the study cohort are shown in Fig. 1.

Fig. 1.

Inclusion criteria of 30,806 cases and 162,463 controls with delivery during the COVID-19 pandemic or during pre-pandemic times in Austria

When comparing the descriptive characteristics, women in the COVID-19 pandemic period were one year older at the time of their pregnancy (31 [27–34] years vs. 30 [27–34] years, p < 0.001) and were more often nullipara (55.41% vs. 50.64%, p < 0.001) than the women in the pre-pandemic period group. The median gestational age did was comparable between the COVID-19 pandemic group (39 [35, 36] weeks) and the pre-pandemic period group (39 [35–37] weeks; p = 0.96). The maternal and neonatal characteristics of births during pandemic versus pre-pandemic periods are given in Table 1.

Table 1.

Maternal and neonatal characteristics of 30.806 cases and 162.463 controls with delivery during the COVID-19 pandemic compared to pre-pandemic times in Austria

Variables	Frequency (proportion, %) or Median (minimum-maximum)		P value
	COVID-19 pandemic	Pre-Pandemic times
Maternal characteristics
Age	31 (27–34)	30 (27–34)	p < 0.001
Nullipara	17,069 (55.41%)	82,260 (50.64%)	p < 0.001
Weight (kilograms)	64 (57–73)	63 (56–72)	p < 0.001
Height (centimeter)	166 (162–170)	166 (162–170)	p = 0.09
BMI (kg/m 2 )	23.03 (20.70–26.37)	22.7 (20.57–22.77)	p < 0.001
Neonatal characteristics
Neonatal gender
male	15,775 (51.21%)	83,125 (51.17%)	0.892
female	15,030 (48.79%)	79,298 (48.81%)	0.947
undefined	1 (< 0.01%)	40 (0.02%)	0.018
Gestational age (weeks)	39 (39–40)	39 (38–40)	p = 0.96
Birthweight (grams)	3,410 (3,130–3,710)	3,400 (3,120- 3,700)	< 0.001
Head circumference (centimeter)	34 (34–36)	35 (34–36)	< 0.001
Birthheight (centimeter)	51 (50–53)	51 (50–52)	< 0.001
Umbilical cord arterial pH	7.26 (7.21–7.32)	7.27 (7.21–7.33)	< 0.001
5-minute Apgar score < 7	213 (0.69%)	1,053 (0.65%)	0.393

Pre-pregnancy weight and weight gain during pregnancy

The median body weight and BMI of women before their pregnancies were 64 (57–73) kg and 23.03 (20.70–26.37) kg/m² during the COVID-19 pandemic versus 63 (56–72) kg and 22.7 (20.57–22.77) kg/m² during the pre-pandemic period (p < 0.001). The weight and BMI difference of 1 kg and 0.3 kg/m² turned out to be significant (p < 0.001) between the pandemic and pre-pandemic periods. Weight gain and BMI increase over the course of pregnancy remained constant at 13 (5.76) kg and 4.8 (2.09) kg/m², respectively, between the COVID-19 period and the pre-pandemic period (p = 0.69; p = 0.65). After adjusting for covariates (age, height, parity), multivariate analysis revealed that the COVID-19 pandemic had a significant impact on pre-pregnancy body weight (OR 1.01; 95% CI 1.00–1.02; p < 0.001) (Table 2).

Table 2.

Multivariate logistic regression model of variables predicting maternal pre-pregnancy body weight

	Pre-pregnancy weight		P value
	OR	95% CI
COVID-19 pandemic	1.01	1.00–1.02	< 0.001
Age	0.99	0.99–0.10	0.004
Height	1.01	1.01–1.01	0.004
Parity	1.02	1.01–1.03	< 0.001

Changes in the BMI classes of pregnant women

During the COVID-19 pandemic period, the percentage of women with a pre-pregnancy BMI defined as overweight and obesity classes I-III was significantly higher compared to pre-pandemic times (p < 0.003, p < 0.001, p < 0.001, p = 0.001). This increase was most pronounced in overweight women. The number of women with underweight (5.38% vs. 5.95%) and normal weight (61.55% vs. 62.96%) was lower during the COVID-19 pandemic compared to pre-pandemic times (both: p < 0.0010). The changes in BMI classes between the exposure and control periods are shown in Fig. 2.

Fig. 2.

Changes in the BMI classes of pregnant women from the pre-pandemic times to the COVID-19 pandemic

Delivery-associated complications

When analyzing delivery-associated complications during the observational periods, we found a significantly higher rate of macrosomia (p = 0.003) and vacuum-assisted deliveries (p = 0.020) among cases in the pandemic compared to pre-pandemic times. All tested birth complications are shown in Table 3.

Table 3.

Delivery-associated complications of 30.806 cases and 162.463 controls with delivery during the COVID-19 pandemic compared to pre-pandemic times in Austria

Variables	Frequency (proportion, %)		P value
	COVID-19 pandemic	Pre-Pandemic times
Macrosomia	2,898 (9.42%)	14,433 (8.89%)	0.003
Vacuum-assisted deliveries	2,611 (8.48%)	13,051 (8.09%)	0.020
High-grade perineal laceration	478 (1.55%)	2,741 (1.69%)	0.088
Episiotomy	3,301 (10.72%)	18,041 (11.10%)	0.050
Shoulder dystocia	110 (0.36%)	224 (0.14%)	0.783
Non-elective c-section	4,237 (13.76%)	22,060 (13.57%)	0.652

Discussion

The findings of this epidemiologic study highlight the health sequalae of the COVID-19 pandemic, specifically weight- and obesity-related complications of pregnant women, despite the fact that the acute crisis is over. Both, a higher pre-pregnancy weight and BMI, as well as an increased proportion of overweight and obese women conceiving, were identified during the pandemic period. Subsequently, more delivery-associated complications, specifically macrosomic infants and vacuum deliveries, occurred from May 1 to December 31, 2020, than during the pre-pandemic times.

To prevent the rapid transmission of the COVID-19 virus, and subsequently the overburdening of the healthcare systems, governments-imposed restrictions on social gatherings and outdoor activities and forced collective repeated lockdowns and quarantining [2]. These measures led to dramatic changes in lifestyles, including a reduction in physical activity, gyn closures, alterations in individuals’ eating habits, remote work, homeschooling, and e-learning [3, 6–11, 38].

A body of literature has reported that virus-mitigating measures significantly worsened the concurrent and escalating pandemic of obesity in people of all age groups [7, 22, 24]. However, evidence as to whether the pandemic also affected weight and obesity-related complications in the subset of women conceiving is only just emerging [23, 24]. An Australian cohort study revealed, in line with our data, initial findings demonstrating an increase in pre-pregnancy BMI of 0.2 kg/m² and a higher proportion of obese pregnant women during the pandemic, compared to pre-pandemic periods [23]. Because the primary focus of the study was to evaluate whether the COVID-19 pandemic heightened the risk of gestational diabetes, the authors included only pregnant women who underwent a 75 g oral glucose tolerance test (OGTT) as part of their pregnancy care. However, this test was not administered in more than 20% of cases [23]. This could have led to potential bias in that only women at high risk for gestational diabetes mellitus (GDM) who underwent an OGTT during the COVID-19 pandemic and repeated lockdowns were included in the exposure group and compared to a low-risk pre-pandemic group. This assumption is reinforced by the demographic data showing that the COVID-19 group reflected a significantly higher proportion of pregnant women with both a prior history of GDM and a first-degree family member or sister with diabetes compared to the pre-pandemic control group [23]. The study provides important results concerning the increase in the rate of GDM during the pandemic; however, it does not allow for a valid interpretation of the weight and BMI changes in pregnant women during the pandemic period.

No significant differences in pre-pregnancy weight and BMI were found in the single-center cohort study by Raischer et al. [24]. However, it was shown that women gained more weight during their pregnancy and therefore had a higher weight following birth [24]. The authors included cases from April 2020, during which lockdowns had just been implemented in most countries. Therefore, the timeline was definitely too short to determine whether lockdowns, which had just been executed, affected pre-pregnancy metabolic status. Hence, the exposure period in our multicenter cohort study features a 4-week delay, starting in May and ending in December 2020. By following this exact study design, our data highlighted a weight and BMI difference of 1 kg and 0.3 kg/m² in women compared to the start of their pregnancies, which is comparable to data in non-pregnant cohorts found by several authors [7, 22].

Analyzing the pre-pregnancy weight and BMI are important for prenatal care, as overweight and obesity are associated with both adverse maternal and neonatal health outcomes [25, 27, 28, 30]. They have been shown to exacerbate comorbidities, such as pregnancy-induced hypertension, insulin resistance, GDM, and infectious states, in parturient mothers. Additionally, they can heighten the risk for fetal malformations and anomalies, increase fetal birth weight, and subsequently alter various aspects of the mode of delivery [35–37, 39–42]. In this vein, our data revealed more newborns with macrosomia and a higher proportion of vacuum-assisted vaginal deliveries during the pandemic period than during pre-pandemic times.

However, the impact of maternal obesity goes beyond the newborn period. Emerging evidence has revealed that fetal programming during the critical window of pregnancy can have long-term detrimental effects on the offspring and future generations [25]. The authors uncovered links between maternal obesity and alterations in macronutrient availability, epigenetic modifications, and inflammation. There is often an interplay between all these factors, resulting in a compounded effect on the long-term outcome of the offspring, including increased risk of child and adulthood obesity and ultimately metabolic syndrome [25, 27, 43, 44]. Finally, pre-pregnancy (over)weight is also a strong determinant for a woman’s long-term obesity [27]. Therefore, there is an urgent need to pinpoint pandemic-related worsening of overweight and obesity in women and the offspring as a global health priority due to the enormous longstanding burden it will generate, even though the acute crisis is over.

GWG is another parameter that can be used to monitor the metabolic status of pregnant women [30]. An increase in weight during pregnancy is necessary to ensure a healthy fetal development. However, inappropriate weight gain significantly increases the risk of pregnancy complications [35, 37, 41, 45, 46]. Notably, the literature has suggested that maternal pre-pregnancy BMI–compared to GWG–is more strongly associated with adverse outcomes and metabolic alterations in the offspring [30]. For example, Catalano et al. specifically found that a maternal pre-pregnancy BMI greater than 30 kg/m²–compared to GWG–more significantly correlated with an increased body fat percentage in offspring at age 8 [27, 44]. Interestingly, in our study, we found that pre-pregnancy obesity significantly differed between the pandemic and pre-pandemic groups, but not GWG, emphasizing the long-term importance of our results.

The prevalence of overweight and obese women of reproductive ages has increased dramatically in the last decades of the 20th century, especially in high-income countries, making it one of the most important public health concerns worldwide [47, 48]. As reported by previously published studies, the COVID-19 pandemic and related mitigating measures have led to an exacerbation of this already escalating health issue [7, 22]. Our study revealed that in pregnant women, the percentage of overweight and morbid obesity increased dramatically during the pandemic compared to pre-pandemic times. Conversely, the number of pregnant women with normal weight and underweight has decreased. It is alarming that at least 2.8 million deaths per year are caused by obesity (BMI ≥ 30 kg/m²), according to WHO [31]. This is almost more death events per year than the direct causes of COVID-19 itself [31]. Therefore, it is imperative to engage in collaborative actions and interventions to address the double burden of COVID-19 and obesity in worsening maternal and childhood health as part of post-pandemic recovery efforts. Prenatal health care providers would have to constantly promote lifestyle interventions incorporating counselling about diet, physical activity, and behavioral components regardless of their patients´ current weight status; and most importantly, low- or no-cost access to such physical activity programs (e.g. group appointments), nutrition educational sessions, and trainings in behavioral techniques would have to be ensured.

The findings of our study add to the growing body of observational evidence that the COVID-19 pandemic worsened the complex issue of obesity [7, 17, 22–24, 49]. The strength of the study lies in its comprehensive approach, which jointly examines pre-pregnancy weight, pre-pregnancy BMI, and GWG during the COVID-19 pandemic in comparison with pre-pandemic periods, and relates these parameters to delivery-related complications. This integrated analysis extends previous work that has largely focused on single anthropometric measures. The study periods were defined cautiously with the pandemic group featuring a 4-week delay to the onset of the first national lockdown, in order to ensure that the first effects of the COVID-19-associated restrictions on individual body weight and BMI were measurable. Although self-reported pre-pregnancy weight was documented immediately upon confirmation of pregnancy, the possibility of recall and reporting bias cannot be entirely excluded. The main weakness of our study is its retrospective nature, which is accompanied by the inherited limitation associated with establishing a causal relationship between the pandemic crisis and obesity-related parameters. However, the nationwide setting enabled the availability of an enormously large dataset, which yielded robust estimates of significant factors, including the pandemic period, which was shown to influence pre-pregnancy body weight. To more robustly disentangle pandemic-related effects from underlying temporal trends, future studies should incorporate multiple pre-pandemic years and employ formal trend-adjusted or interrupted time-series analyses.

Conclusions

We found that COVID-19-mitigating measures worsened the concurrent pandemic of obesity in pregnant women. Adverse short- and long-term consequences for both mothers and newborns are likely to occur. To counteract these, targeted intervention programs focusing on a healthy lifestyle in pregnancy and childhood should be implemented and must be an integral part of pandemic recovery plans.

Abbreviations

BMI

Body mass index

CI

Confidence interval

COVID-19

Coronavirus disease 2019

GDM

Gestational diabetes mellitus

GWG

Gestational weight gain

OGTT

Glucose tolerance test

OR

Odds ratio

WHO

World Health Organization

Authors’ contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by SN and ID. KW and AF interpretated the data. HK, AF and DM provided clinical support. The first draft of the manuscript was written by KW. All authors critically revised and commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

No funds, grants, or other support was received.

Data availability

The datasets generated during the current study are not publicly available because they contain sensitive data to be treated under data protection laws and regulations. Appropriate forms of data sharing can be arranged after a reasonable request to the corresponding author.

Declarations

Ethics approval and consent to participate

The study was conducted in accordance with the Declaration of Helsinki and the Good Clinical Practice guidelines. The study has been approved by the Ethics Committee of the Medical University of Vienna (reference number 1637/20). Because of the study’s retrospective character, the ethics committee waived the need for informed consent of the study subjects. All patient data were de-identified before analyses.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.