Association of extremes of prepregnancy BMI with the clinical presentations of preterm birth

Impact of being underweight before pregnancy on preterm birth by race/ethnicity and insurance status in California: an analysis of birth records

BACKGROUND

The US still has a high burden of preterm birth (PTB), with important disparities by race/ethnicity and poverty status. There is a large body of literature looking at the impact of pre-pregnancy obesity on PTB, but fewer studies have explored the association between underweight status on PTB, especially with a lens toward health disparities. Furthermore, little is known about how weight, specifically pre-pregnancy underweight status, and socio-economic-demographic factors such as race/ethnicity and insurance status, interact with each other to contribute to risks of PTB.

OBJECTIVES

The objective of this study was to measure the association between pre-pregnancy underweight and PTB and small for gestational age (SGA) among a large sample of births in the US. Our secondary objective was to see if underweight status and two markers of health disparities - race/ethnicity and insurance status (public vs. other) - on PTB.

STUDY DESIGN

We used data from all births in California from 2011 to 2017, which resulted in 3,070,241 singleton births with linked hospital discharge records. We ran regression models to estimate the relative risk of PTB by underweight status, by race/ethnicity, and by poverty (Medi-cal status). We then looked at the interaction between underweight status and race/ethnicity and underweight and poverty on PTB.

RESULTS

Black and Asian women were more likely to be underweight (aRR = 1.0, 95% CI: 1.01, 1.1 and aRR = 1.4, 95% CI: 1.4, 1.5, respectively), and Latina women were less likely to be underweight (aRR = 0.7, 95% CI: 0.7, 0.7). Being underweight was associated with increased odds of PTB (aRR = 1.3, 95% CI 1.3-1.3) and, after controlling for underweight, all nonwhite race/ethnic groups had increased odds of PTB compared to white women. In interaction models, the combined effect of being both underweight and Black, Indigenous and People of Color (BIPOC) statistically significantly reduced the relative risk of PTB (aRR = 0.9, 95% CI: 0.8, 0.9) and SGA (aRR = 1.0, 95% CI: 0.9, 1.0). The combined effect of being both underweight and on public insurance increased the relative risk of PTB (aRR = 1.1, 95% CI: 1.1, 1.2) but there was no additional effect of being both underweight and on public insurance on SGA (aRR = 1.0, 95% CI: 1.0, 1.0).

CONCLUSIONS

We confirm and build upon previous findings that being underweight preconception is associated with increased risk of PTB and SGA - a fact often overlooked in the focus on overweight and adverse birth outcomes. Additionally, our findings suggest that the effect of being underweight on PTB and SGA differs by race/ethnicity and by insurance status, emphasizing that other factors related to inequities in access to health care and poverty are contributing to disparities in PTB.

Pre-pregnancy body mass index and low birthweight: Secondary data analysis using health insurance claims data in Japan

AIM

For women, being underweight increases their susceptibility to osteoporosis, anemia, and other conditions and affects the weight of their infants and the well-being of future generations. This study examined the association between low pre-pregnancy body mass index (BMI) and low birthweight using health insurance claims data and health checkup data, including weight measurements.

METHODS

We used health insurance claims data and health checkup data (JMDC, Tokyo, Japan) of women and their newborns in Japan between 2006 and 2020. We used checkup data, which included more accurate weight measurements and blood test-based diagnoses of anemia and hyperlipidemia compared to self-reported data. Maternal pre-pregnancy BMI was compared across three groups: underweight (BMI <18.5 kg/m2), normal weight (BMI 18.5-24.9 kg/m2), and overweight (BMI ≥25.0 kg/m2). The primary outcome was low birthweight (<2500 g), and secondary outcome was preterm childbirth. Logistic regression analyses were conducted to compare outcomes in the three groups by BMI. The underweight BMI group was considered as the reference group. A subgroup analysis was performed by maternal age.

RESULTS

In total, 16 363 mothers (underweight, 3418 [21%], normal weight, 11 493 [70%], and overweight, 1452 [8.9%]) were included. The risk of primary outcome (low birthweight) was significantly lower in the normal weight group than in the underweight group (4.6% vs. 5.7%; adjusted odds ratio 0.78 [95% confidence interval: 0.65-0.96]). In the subgroup analyses, no significant differences were noted in the incidences of low birthweight and preterm childbirth between maternal age groups.

CONCLUSIONS

Pre-pregnancy BMI was associated with an increased risk of delivering low-birthweight infant. Awareness about the importance of women's pre-pregnancy health and appropriate BMI may reduce the incidence of low birthweight.

Association between maternal cigarette smoking cessation and risk of preterm birth in Western New York

BACKGROUND

Although many studies suggested the benefit of smoking cessation among pregnant women in reducing the risk of preterm birth (PTB), the timing of the effect of the cessation remains inconclusive.

OBJECTIVES

To examine the association of trimester-specific smoking cessation behaviours with PTB risk.

METHODS

We included 199,453 live births in Western New York between 2004 and 2018. Based on self-reported cigarette smoking during preconception and in each trimester, we created six mutually exclusive groups: non-smokers, quitters in each trimester, those who smoked throughout pregnancy, and inconsistent smokers. Risk ratios (RRs) and 95% confidence intervals (CIs) were estimated using Poisson regression to examine the association between smoking cessation and PTB. Effect modification by illegal drug use, maternal age, race and ethnicity and pre-pregnancy body mass index (BMI) was investigated multiplicatively by ratio of relative risk and additively by relative excess risk due to interaction (RERI).

RESULTS

Overall, 6.7% of women had a PTB; 14.1% smoked throughout pregnancy and 3.4%, 1.8% and 0.8% reported quitting smoking during the first, second and third trimesters, respectively. Compared to non-smokers, third-trimester cessation (RR 1.20, 95% CI 1.01, 1.43) and smoking throughout pregnancy (RR 1.27, 95% CI 1.21, 1.33) were associated with a higher PTB risk, while quitting smoking during the first or second trimester, or inconsistent smoking was not associated with PTB. A positive additive interaction was identified for maternal age and late smoking cessation or smoking throughout pregnancy on PTB risk (RERI 0.17, 95% CI 0.00, 0.36), and a negative interaction was observed for pre-pregnancy BMI ≥30 kg/m2 (ratio of relative risk 0.70, 95% CI 0.63, 0.78; RERI -0.42, 95% CI -0.56, -0.30).

CONCLUSION

Compared to non-smokers, smoking throughout pregnancy and third-trimester smoking cessation are associated with an increased risk of PTB, while quitting before the third trimester may not increase PTB risk.

Microbiome preterm birth DREAM challenge: Crowdsourcing machine learning approaches to advance preterm birth research

Every year, 11% of infants are born preterm with significant health consequences, with the vaginal microbiome a risk factor for preterm birth. We crowdsource models to predict (1) preterm birth (PTB; <37 weeks) or (2) early preterm birth (ePTB; <32 weeks) from 9 vaginal microbiome studies representing 3,578 samples from 1,268 pregnant individuals, aggregated from public raw data via phylogenetic harmonization. The predictive models are validated on two independent unpublished datasets representing 331 samples from 148 pregnant individuals. The top-performing models (among 148 and 121 submissions from 318 teams) achieve area under the receiver operator characteristic (AUROC) curve scores of 0.69 and 0.87 predicting PTB and ePTB, respectively. Alpha diversity, VALENCIA community state types, and composition are important features in the top-performing models, most of which are tree-based methods. This work is a model for translation of microbiome data into clinically relevant predictive models and to better understand preterm birth.

Factors Associated with Spontaneous Preterm Birth after Ultrasound-Indicated Cerclage

Ultrasound-indicated cerclage (UIC) is recommended to prevent spontaneous preterm birth (sPTB) in women with a short cervix at mid-trimester and a history of PTB. We assessed the factors related to sPTB after UIC and determined the corresponding risks. This retrospective cohort study was conducted at a university hospital. UIC was performed between 15 and 26 weeks of gestation in women with a cervical length of <2.5 cm. Univariate and multivariate analyses were used to examine factors associated with sPTB after UIC. An earlier gestational age and shorter cervical length at UIC were associated with sPTB after UIC. While PTB history was not associated with an increased risk of sPTB, it did increase the risk of repeat cerclage after UIC. Higher levels of preoperative serum inflammatory markers and obesity significantly increased the risk of sPTB after UIC. These findings provide helpful guidance for patient counseling and management in predicting the delivery timing after UIC in women with a short cervix in the mid-trimester.

Impact of pre-pregnancy weight on the risk of premature rupture of membranes in Chinese women

Objective

The objective of this study was to investigate the influence of pre-pregnancy body mass index (BMI) on the incidence of premature rupture of membranes (PROM) among Chinese women.

Methods

This was a hospital-based retrospective cohort study of 75,760 Chinese women who had live singleton births between 2016 and 2020. In this study, we utilized logistic regression analysis to estimate the association between pre-pregnancy BMI and PROM based on gestational age.

Results

Prior to pregnancy, being overweight or obese was found to be significantly associated with an increased risk of preterm premature rupture of membranes (PPROM), as evidenced by adjusted odds ratios and 95 % confidence intervals of 1.336 (1.173-1.522) and 1.411 (1.064-1.872), respectively. Those with PPROM were divided into three groups according to gestational age: 22-27, 28-31, and 32-36 weeks. Women who were overweight or obese prior to pregnancy had a higher likelihood of experiencing PROM between 22 and 27 weeks of gestation. This finding remained consistent even after controlling for potential confounding factors, such as gestational diabetes mellitus (GDM), gestational hypertension, preeclampsia, hydramnios, cervical abnormalities, and a history of preterm birth.

Conclusion

Our research findings indicate that being overweight or obese before pregnancy is linked to a higher likelihood of experiencing PPROM. Therefore, achieving optimal weight before pregnancy is important to prevent PPROM and its associated complications.

Obesity as a potential risk factor for stillbirth: The Japan Environment and Children's Study

The relationship between high body mass index (BMI) >25 kg/m2 and risk for stillbirth in the Japanese population remains unclear. This study aimed to estimate the impact of maternal obesity on the risk of stillbirth in a Japanese population. This prospective cohort study used data from the Japan Environment and Children's Study, which recruited pregnant individuals between 2011 and 2014. A total of 93,772 fetuses were considered eligible for inclusion in this study. Stillbirth (fetal death before or during labor at ≥22 completed weeks of gestation) rates were compared among four pre-pregnancy BMI groups: underweight (<18.5 kg/m2), reference (18.5 to <25.0 kg/m2), overweight (25.0 to <30.0 kg/m2), and obese (≥30.0 kg/m2). The association between pre-pregnancy BMI and the risk of stillbirth was estimated using multiple logistic regression analyses. The overall stillbirth incidence was 0.33% (305/93,722). Compared with the reference group, the risk of stillbirth was significantly higher in the overweight group (adjusted odds ratio [aOR]: 1.55; 95% confidence interval [CI]: 1.08-2.23) and the obese group (aOR: 2.60; 95% CI: 1.59-4.24). The overall incidence of early stillbirth (i.e., <28 weeks) was 0.17% (155/93,722). Similarly, after adjusting for potential confounding factors, the risk of early stillbirth was significantly higher in the obese group (aOR: 4.33; 95% CI: 2.44-7.70). Increased maternal BMI was associated with an increased risk of stillbirth in the Japanese population. Therefore, counselling women planning for pregnancy on the importance of an appropriate pre-pregnancy BMI to minimize the risk of stillbirth is important.

Monitoring gestational weight gain: setting up a regional surveillance system in Italy

BACKGROUND

In many countries, including Italy, there are few national data on pre-pregnancy Body Mass Index (BMI) and gestational weight gain (GWG), despite these being important predictors of maternal and neonatal health outcomes. This dearth of information makes it difficult to develop and monitor intervention policies to reduce the burden of disease linked to inadequate BMI status and/or GWG in pregnant women. This study describes the setting up and initial implementation of a regional surveillance system on pre-pregnancy BMI and GWG.

METHODS

Between 1 January 2017 and 31 December 2018, anthropometric data were collected from all pregnant women accessing public health services in the Friuli Venezia Giulia region (Italy) for first ultrasound check (T1) and at delivery (T2). Anthropometric data collected at T1 (self-reported pre-pregnancy weight and measured weight and height) and T2 (measured weight and self-reported pre-pregnancy weight and height) were compared.

RESULTS

The system was able to reach 43.8% of all the women who gave birth in the region, and provided complete data for 6400 women of the 7188 who accessed the services at T1. At the beginning of pregnancy 447 (7.0%) women were underweight, 4297 (67.1%) had normal weight, 1131 (17.7%) were overweight and 525 (8.2%) had obesity. At delivery, 2306 (36.0%) women were within the appropriate weight gain range, while for 2021 (31.6%) weight gain was insufficient and for 2073 (32.4%) excessive. Only minor differences were observed between measured and self-reported anthropometric data.

CONCLUSIONS

The surveillance system offers an overview of the weight status of women during pregnancy. About 1/3 of women entered pregnancy with unsatisfactory BMI and 2/3 did not achieve the recommended weight gain. This surveillance system can be an effective tool to guide public health interventions.

Association Between Obesity and Fetal Acidosis at Scheduled Cesarean Delivery

OBJECTIVE

To evaluate whether patients with obesity who undergo scheduled cesarean delivery under neuraxial anesthesia are at increased risk for umbilical artery pH less than 7.1 and base deficit 12 mmol or greater.

METHODS

We conducted a multicenter, retrospective cohort study of individuals who delivered a term, singleton, nonanomalous neonate at one of four academic medical centers in New York City from 2013 to 2019 by scheduled cesarean under neuraxial anesthesia for whom fetal cord blood gas results were available. The primary study outcome was rate of fetal acidosis , defined as umbilical artery pH less than 7.1. This was compared between patients with obesity (body mass index [BMI] 30 or higher) and those without obesity (BMI lower than 30). Base deficit 12 mmol or greater and a composite of fetal acidosis and base deficit 12 mmol or greater were also compared. Secondary outcomes included neonatal intensive care unit admission rate, 5-minute Apgar score less than 7, and neonatal morbidity. Associations between maternal BMI and study outcomes were assessed using multivariable logistic or linear regression and adjusted for age, race and ethnicity, insurance type, cesarean delivery order number, and neuraxial anesthesia type.

RESULTS

Of the 6,264 individuals who met inclusion criteria during the study interval, 3,098 had obesity and 3,166 did not. The overall rate of umbilical artery cord pH less than 7.1 was 2.5%, and the overall rate of umbilical artery base deficit 12 mmol or greater was 1.5%. Patients with obesity were more likely to have umbilical artery cord pH less than 7.1 (adjusted odds ratio [aOR] 2.7, 95% CI 1.8-4.2) and umbilical artery base deficit 12 mmol or greater (aOR 3.2, 95% CI 1.9-5.3). This association was not significantly attenuated after additional adjustments for potential mediators, including maternal medical comorbidities. We found no differences in secondary outcomes between groups.

CONCLUSION

Maternal obesity is associated with increased odds of arterial pH less than 7.1 and base deficit 12 mmol or greater at the time of scheduled cesarean delivery under neuraxial anesthesia.

What Role Does Hispanic/Latina Ethnicity Play in the Relationship Between Maternal Mental Health and Preterm Birth?

OBJECTIVE

To investigate the association of prepregnancy and prenatal depression and/or anxiety on preterm birth (PTB), while also exploring Hispanic/Latina ethnicity as a potential effect modifier.

METHODS

Study population included respondents of UT-PRAMS (2016-2019). Associations between prepregnancy and prenatal depression and/or anxiety and PTB were evaluated using Poisson regression models accounting for stratified survey sampling.

RESULTS

Women with prepregnancy and prenatal depression and anxiety, compared to those without, had a 67 percent (95% CI: 19%, 134%) higher probability of experiencing PTB, after controlling for relevant sociodemographic, lifestyle, and reproductive history factors. Impact of depression on PTB was slightly higher than impact of anxiety. Hispanic/Latina ethnicity was found to protect against PTB for those with prepregnancy and prenatal depression alone (aPR: 0.53, 95% CI: 0.24, 1.21) or both depression and anxiety (aPR: 0.51, 95% CI: 0.18, 1.40) compared to being non-Hispanic/Latina (aPR: 1.79, 95% CI: 1.25, 2.55 for depression alone; aPR: 1.62, 95% CI: 1.18, 2.21 for depression and anxiety).

CONCLUSIONS

Overall, Utah women reporting prepregnancy and prenatal depression and anxiety were more likely to have a PTB. Being of Hispanic/Latina ethnicity was found to mitigate the risk of PTB among women with depression and anxiety.

IMPLICATIONS

Prepregnancy and prenatal mental health screenings and treatment are key to lessening the impacts of depression and anxiety on both mother and infant. Hispanic/Latina ethnicity may be protective against PTB among women experiencing mental distress. Whether this is through increased social support or through a different mechanism should be explored in future research.

Obstetric outcomes during delivery hospitalizations among obese pregnant women in the United States

The rates of both maternal and fetal adverse outcomes increase significantly with higher body mass index. The aim of this study was to calculate national estimates of adverse maternal and fetal outcomes and associated hospitalization cost among obese pregnant women using a national database. This study was a retrospective analysis of data retrieved from Nationwide Inpatient Sample database, collected during 2010–2014. The primary outcomes of this study were adverse maternal and fetal outcomes, hospital length of stay, and hospitalization cost. There was a total of 18,687,217 delivery-related hospitalizations, of which 1,048,323 were among obese women. Obese women were more likely to have cesarean deliveries (aOR 1.70, 95% CI 1.62–1.79) and labor inductions (aOR 1.51, 95% CI 1.42–1.60), greater length of stay after cesarean deliveries (aOR 1.14, 95% CI 1.08–1.36) and vaginal deliveries (aOR 1.48, 95% CI 1.23–1.77). They were also more likely to have pregnancy-related hypertension, preeclampsia, gestational diabetes, premature rupture of membranes, chorioamnionitis, venous thromboembolism, excessive fetal growth, and fetal distress. Obese pregnant women had significantly greater risk for adverse obstetrical outcomes, which substantially increased the hospital and economic burden. Risk stratification of pregnant patients based on obesity could also help obstetricians to make better clinical decisions and improve patient outcomes.

Leptin-Induced HLA-G Inhibits Myometrial Contraction and Differentiation

Maternal obesity is associated with a wide spectrum of labour disorders, including preterm birth. Leptin, a pro-inflammatory adipokine and a key factor of obesity, is suspected to play a major role in these disorders. OB-R, its receptor, is expressed on macrophages and myocytes, two cell types critical for labour onset. Macrophages secrete reactive oxygen species/pro-inflammatory cytokines, responsible for myometrial differentiation while myocytes control uterine contractions. In this study, we assessed the effect of leptin on myometrial contraction and differentiation using our validated co-culture model of human primary macrophages and myocytes. We demonstrated that leptin had a different effect on myocytes and macrophages depending on the dose. A low leptin concentration induced a tocolytic effect by preventing myocytes’ contraction, differentiation, and macrophage-induced ROS production. Additionally, leptin led to an increase in HLA-G expression, suggesting that the tocolytic effect of leptin may be driven by HLA-G, a tolerogenic molecule. Finally, we observed that recombinant HLA-G also prevented LPS-induced ROS production by macrophages. Altogether, these data provide a putative molecular mechanism by which leptin may induce immune tolerance and therefore interfere with labour-associated mechanisms. Therefore, HLA-G represents a potential innovative therapeutic target in the pharmacological management of preterm labour.

Severity of low pre-pregnancy body mass index and perinatal outcomes: the Japan Environment and Children's Study

Background

The extremes of maternal pre-pregnancy body mass index (BMI) are known to be risk factors associated with obstetric and adverse perinatal outcomes. Among Japanese women aged 20 years or older, the prevalence of underweight (BMI < 18.5 kg/m²) was 11.5% in 2019. Maternal thinness is a health problem caused by the desire to become slim. This study aimed to investigate the association between the severity of maternal low pre-pregnancy BMI and adverse perinatal outcomes, including preterm birth (PTB), low birth weight (LBW), and small-for-gestational age (SGA).

Methods

We conducted a prospective cohort study using data from the Japan Environment and Children’s Study, which recruited pregnant individuals between 2011 and 2014. Pre-pregnancy BMI was categorized as severe-moderate underweight (BMI < 16.9 kg/m²), mild underweight (BMI, 17.0–18.4 kg/m²), low-normal weight (BMI, 18.5–19.9 kg/m²), high-normal weight (BMI, 20.0–22.9 kg/m²), overweight (BMI, 23.0–24.9 kg/m²), and obese (BMI ≥ 25.0 kg/m²). The high-normal weight group was used as the reference for statistical analyses. Adjusted logistic regression was performed to evaluate the association between pre-pregnancy BMI and PTB, LBW, and SGA.

Results

Of 92,260 singleton pregnant individuals, the prevalence was 2.7% for severe-moderate underweight, 12.9% for mild underweight, and 24.5% for low-normal weight. The prevalence of adverse outcomes was 4.6% for PTB, 8.1% for LBW, and 7.6% for SGA. The adjusted odds ratios (aORs) for PTB were 1.72 (95% confidence interval [CI], 1.46–2.03) for severe-moderate underweight and 1.26 (95% CI, 1.14–1.39) for mild underweight. The aORs of LBW were 2.55 (95% CI, 2.27–2.86) for severe-moderate underweight, 1.64 (95% CI, 1.53–1.76) for mild underweight, and 1.23 (95% CI, 1.16–1.31) for low-normal weight. The aORs of SGA were 2.53 (95% CI, 2.25–2.84) for severe-moderate underweight, 1.66 (95% CI, 1.55–1.79) for mild underweight, and 1.29 (95% CI, 1.21–1.38) for low-normal weight.

Conclusions

A dose-response relationship was found between the severity of low pre-pregnancy BMI and PTB, LBW, and SGA. Even low-normal BMI (18.5–19.9 kg/m²) increased the risk of LBW and SGA. This study provides useful information for pre-conception counseling in lean individuals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-04418-3.

The predicted risk of adverse pregnancy outcomes as a result of treatment-associated obesity in a hypothetical population receiving tenofovir alafenamide/emtricitabine/dolutegravir, tenofovir disoproxil fumarate/emtricitabine/dolutegravir or tenofovir disoproxil fumarate/emtricitabine/efavirenz

OBJECTIVE

Integrase inhibitors, including dolutegravir (DTG), are associated with weight gain and obesity, especially when combined with tenofovir alafenamide (TAF). Obesity increases the risk of adverse pregnancy outcomes (APOs). This study aimed to predict the risk of APOs caused by treatment-associated obesity, using a hypothetical sample based on the ADVANCE trial.

DESIGN

Risk prediction.

METHODS

Firstly, a meta-analysis was performed to determine the relative risk (RR) for APOs in women with obese (≥30) versus normal prepregnancy BMIs (18.5-24.9). For the hypothetical sample, 3000 nonpregnant women with normal BMIs at Week 0 of treatment were evenly allocated across the following treatment arms: TAF/FTC+DTG, TDF/FTC+DTG, TDF/FTC/EFV. The treatment-associated obesity rates from ADVANCE were used to calculate the number of women with obese and normal BMIs expected at Week 96 in our sample. This was combined with the APO RRs to predict the number of women at risk of APOs, in each treatment arm, assuming they conceived at Week 96.

RESULTS

At Week 96, the percentage of women predicted to be obese was 14.1% with TAF/FTC+DTG, 7.9% with TDF/FTC+DTG and 1.5% with TDF/FTC/EFV. The RR in women with obese versus normal BMIs was significantly higher for most APOs. Therefore, the number of women at risk of APOs was higher with TAF/FTC+DTG than TDF/FTC+DTG and TDF/FTC/EFV. For example, 11/1000 additional gestational hypertension cases were predicted with TAF/FTC+DTG, 6/1000 with TDF/FTC+DTG and 1/1000 with TDF/FTC/EFV.

CONCLUSION

Treatment-associated obesity increased the APO risk in women. This risk is likely to increase, as preliminary data from ADVANCE demonstrates ongoing weight gain beyond Week 96.

Preterm Birth and Small-for-Gestational Age Neonates among Prepregnancy Underweight Women: A Case-Controlled Study

The aim of our study was to investigate whether prepregnancy underweight body mass index (BMI) is associated with preterm birth (PTB) and small-for-gestational age (SGA). This retrospective case-control study included 814 women with live singleton fetuses in vertex presentation that gave birth between January 2016 and November 2016 in two tertiary care hospitals. The study group (n = 407) comprised all women whose prepregnancy BMI was underweight (<18.5 kg/m2) and who delivered during the study period. A control group (n = 407) was established with women whose prepregnancy BMI was normal (18.5-24.9 kg/m2) by matching age and parity. Univariate and multivariate analyses were performed to compare PTB and SGA associated with prepregnancy underweight BMI. Compared with the control group, the study group had higher rates of overall PTB (10.1% vs. 5.7%, p = 0.02), iatrogenic PTB (4.2% vs. 1.5%, p = 0.02), and SGA (22.1% vs. 11.1%, p < 0.001). In a multivariable analysis, prepregnancy underweight BMI was associated with PTB (aOR 2.32, 95% CI 1.12-4.81) and with SGA (aOR 2.38, 95% CI 1.58-3.58). In singleton pregnancies, women's prepregnancy underweight compared with normal BMI was associated with an increase in PTB and in SGA neonates. Identifying this specific high-risk group is pragmatic and practical for all physicians, and they should be aware about perinatal outcome among underweight women.

Obesity in Pregnancy: ACOG Practice Bulletin, Number 230

Obstetrician-gynecologists are the leading experts in the health care of women, and obesity is the most common medical condition in women of reproductive age. Obesity in women is such a common condition that the implications relative to pregnancy often are unrecognized, overlooked, or ignored because of the lack of specific evidence-based treatment options. The management of obesity requires long-term approaches ranging from population-based public health and economic initiatives to individual nutritional, behavioral, or surgical interventions. Therefore, an understanding of the management of obesity during pregnancy is essential, and management should begin before pregnancy and continue through the postpartum period. Although the care of the obese woman during pregnancy requires the involvement of the obstetrician or other obstetric care professional, additional health care professionals, such as nutritionists, can offer specific expertise related to management depending on the comfort level of the obstetric care professional. The purpose of this Practice Bulletin is to offer an integrated approach to the management of obesity in women of reproductive age who are planning a pregnancy.

Maternal Pre-conception Body Mass Index and Fasting Plasma Glucose With the Risk of Pre-term Birth: A Cohort Study Including 4.9 Million Chinese Women

Background: To evaluate the associations of pre-conception body mass index (BMI), fasting plasma glucose (FPG) alone and their combination with pre-term birth (PTB) risk.

Methods: We conducted a population-based retrospective cohort study with 4,987,129 reproductive-aged women, who participated in National Free Pre-Pregnancy Checkups Project in 2013–2016 and had a singleton delivery before December 2017 in China. All data analyses were conducted in 2018–2021.

Results: A total of 339,662 (6.81%) women had pre-term deliveries. Compared with women with normal weight and normal glucose, underweight and normal weight were associated with PTB among hypoglycemia women, the adjusted odd ratios (aORs) were 1.24 (95% CI: 1.05–1.48) and 1.16 (95% CI: 1.07–1.25), respectively; underweight, overweight and obesity were associated with PTB among women with normal glucose, the aORs were 1.09 (95% CI: 1.08–1.10), 1.06 (95% CI: 1.05–1.07) and 1.08 (95% CI: 1.05–1.12), respectively; all the BMI groups were significantly associated with PTB among women with pre-diabetes or diabetes (P < 0.05). The dose-response relationships of BMI with PTB varied in different FPG level, with U-shaped curve in normal glucose and pre-diabetes women, J-shaped in diabetes women, L-shaped in hypoglycemia women. For FPG with PTB, the dose-response relationships were U-shaped in normal weight, overweight, and obesity women, and L-shaped in underweight women.

Conclusion: We found that the associations of PTB with BMI varied with levels of FPG, and associations of PTB with FPG varied with levels of BMI. There was a synergistic effect on PTB risk due to abnormal weight and glycemia besides a conventional main effect derived from either of them. Achieving desirable weight and glucose control before conception should be advised.

Association between Maternal Obesity Class, Adherence to Labor Guidelines, and Perinatal Outcomes

Background  Data are limited concerning rates of perinatal complications in women with a body mass index (BMI) ≥40 kg/m2 compared to women with other BMI classes when guidelines for the safe prevention of the primary cesarean delivery are applied. Objective  The aim of the study is to evaluate labor guideline adherence by BMI class and to compare perinatal outcomes across BMI classes with guideline adherent management. Study Design  This retrospective study included low-risk women admitted for delivery between April 2014 and April 2017 after the labor guidelines were implemented. BMI closest to delivery was used for analysis. Women with cesarean for nonreassuring fetal status were excluded. Results  Guideline adherence decreased with increasing BMI, with 93% adherence among women of normal weight compared to 81% for class III obese women ( p  < 0.0001). Among women who had guideline-adherent management, there was increased rates of cesarean among class III versus other obesity classes; however, there were no differences in rates of infectious morbidity ( p  = 0.98) or hemorrhage ( p  = 0.93). Although newborns of women with class III obesity had higher rates of meconium at birth, neonatal outcomes were not different with increasing maternal BMI ( p  = 0.65). Conclusion  There were no differences in adverse perinatal outcomes with increasing BMI.

Impact of Obesity on Outcomes of Pregnancy in Women With Heart Disease

BACKGROUND

Women with heart disease are at risk for complications during pregnancy. This study sought to examine the effect of maternal obesity on pregnancy complications in women with heart disease.

OBJECTIVES

The objective was to determine the incidence of adverse cardiac events (CE) in pregnant women with heart disease and obesity.

METHODS

Adverse CE during pregnancy were examined in a prospective cohort of women with heart disease. CE were a composite of the following: cardiac death/arrest, arrhythmias, heart failure, myocardial infarction, stroke, aortic dissection, and thromboembolic events. Pre-eclampsia and post-partum hemorrhage were also studied. Outcomes were examined according to body mass index (BMI). To identify additional predictors of CE, a baseline risk score (CARPREG [Canadian Cardiac Disease in Pregnancy Study] II score) for predicting cardiac complications was calculated for all pregnancies and included in a multivariable logistic regression model.

RESULTS

Of 790 pregnancies, 19% occurred in women with BMI ≥30 kg/m² (obesity), 25% in women with BMI 25 to 29.9 kg/m² (overweight), 53% in women with BMI 18.5 to 24.9 kg/m² (normal weight), and 3% in women with BMI <18.5 kg/m² (underweight). Women with obesity were at higher risk of CE when compared with women with normal weight (23% vs. 14%; p = 0.006). In a multivariable model, obesity (odds ratio: 1.7; 95% confidence interval: 1.0 to 2.7) and higher CARPREG II risk scores (odds ratio: 1.7; 95% confidence interval: 1.5 to 1.9) predicted CE. Pre-eclampsia was more frequent in women with obesity compared with those with normal weight (8% vs. 2%; p = 0.001).

CONCLUSIONS

Obesity increases the risk of maternal cardiovascular complications in pregnant women with heart disease. This modifiable risk factor should be addressed at the time of preconception counseling.

Adverse effects of pre-pregnancy maternal underweight on pregnancy and perinatal outcomes in a freeze-all policy

BACKGROUND

Underweight and overweight may affect reproduction and interfere with treatment of infertility. In the present retrospective analysis, we sought to evaluate the effect of low body mass index (BMI) on pregnancy and perinatal outcomes in frozen-thawed embryo transfer (FET) cycles.

METHODS

This study involved 8755 FET cycles in a single IVF center during the period from January 2009 to December 2018. Both pregnancy and perinatal outcomes were assessed in women who were underweight, normal weight, and overweight as defined based on a respective BMI < 18.5 kg/m², ≥ 18.5 BMI < 24.9 kg/m², and BMI ≥ 25 kg/m².

RESULTS

Being underweight was linked to reduced implantation rates as compared to a normal weight (33.56% vs. 37.26%). Similarly, when comparing outcomes in underweight women to those in normal weight women, rates of clinical pregnancy (48.14% vs. 53.85%) and ongoing pregnancy (43.04% vs. 50.47%) were reduced. Rates of miscarriage were markedly reduced in the normal weight group relative to the overweight group (10.73% vs. 13.37%). Perinatal outcomes were largely comparable for all groups, with the exception of very low birth weight rates (normal weight:0.58% vs. overweight: 2.03%), very small for gestational age rates (normal weight:1.31% vs. overweight:3.55%) and very preterm delivery rates (normal weight:0.82% vs. overweight: 2.03%), which were significantly elevated for overweight mothers.

CONCLUSIONS

These results indicate that being underweight is linked to negative pregnancy outcomes when undergoing FET-based IVF.

Association of pre-pregnancy body mass index with adverse pregnancy outcome among first-time mothers

Background

Studies have reported an increased risk of adverse pregnancy outcome associated with pre-pregnancy body mass index (BMI). However, the data on such associations in urban areas of southern Chinese women is limited, which drive us to clarify the associations of pre-pregnancy BMI and the risks of adverse pregnancy outcomes (preterm birth (PTB) and low birth weight (LBW)) and maternal health outcomes (gestational hypertension and cesarean delivery).

Methods

We performed a hospital-based case-control study including 3,864 Southern Chinese women who gave first birth to a live singleton infant from January 2015 to December 2015. PTB was stratified into three subgroups according to gestational age (extremely PTB, very PTB and moderate PTB). Besides, we combined birth weight and gestational age to dichotomise as being small for gestational age (SGA, less than the tenth percentile of weight for gestation) and non-small for gestational age (NSGA, large than the tenth percentile of weight for gestation), gestational week was also classified into categories of term, 34-36 week and below 34 week.. We then divided newborns into six groups: (1) term and NSGA; (2) 34–36 week gestation and NSGA; (3) below 34 week gestation and NSGA; (4) term and SAG; (5) 34–36 week gestation and SAG; (6) below 34 week gestation and SAG. Adjusted logistic regression models was used to estimate the odds ratios of adverse outcomes.

Results

Underweight women were more likely to give LBW (AOR = 1.44, 95% CI [1.11–1.89]), the similar result was seen in term and SAG as compared with term and NSAG (AOR = 1.78, 95% CI [1.45–2.17]), whereas underweight was significantly associated with a lower risk of gestational hypertension (AOR = 0.45, 95% CI [0.25–0.82) and caesarean delivery (AOR = 0.74, 95% CI [0.62–0.90]). The risk of extremely PTB is relatively higher among overweight and obese mothers in a subgroup analysis of PTB (AOR = 8.12, 95% CI [1.11–59.44]; AOR = 15.06, 95% CI [1.32–172.13], respectively). Both maternal overweight and obesity were associated with a greater risk of gestational hypertension (AOR = 1.71, 95% CI [1.06–2.77]; AOR = 5.54, 95% CI [3.02–10.17], respectively) and caesarean delivery (AOR = 1.91, 95% CI [1.53–2.38]; AOR = 1.85, 95% CI [1.21–2.82], respectively).

Conclusions

Our study suggested that maternal overweight and obesity were associated with a significantly higher risk of gestational hypertension, caesarean delivery and extremely PTB. Underweight was correlated with an increased risk of LBW and conferred a protective effect regarding the risk for gestational hypertension and caesarean delivery for the first-time mothers among Southern Chinese.

Regulation of Keap-1/Nrf2 Signaling Pathway Is Activated by Oxidative Stress in Patients with Premature Rupture of Membranes

Background

The potential mechanisms underlying premature rupture of membrane (PROM) is still unknown. The aim of this study was to determine the role of Keap-1/Nrf2 signaling pathway activation by oxidative stress in patients with preterm premature rupture of membranes.

Material/Methods

Placental tissues from preterm premature rupture of membranes (PPROM) (n=20), full-term premature rupture of membranes (FPROM) (n=20), and normal-term births (n=20) were collected and amniotic tissues were separated from the placental tissues from pregnant women at Shandong Provincial Qianfoshan Hospital. RT-PCR and Western blot were used to detect the levels of factors in the Keap-1/Nrf2 signaling pathway. To investigate the roles of Nrf2, we downregulated Nrf2 expression using siRNA in primary human amniotic epithelial (HAE) cells.

Results

Among the control group, FPROM group, and PPROM group, the reactive oxygen species (ROS) levels were significantly increased in the FPROM and PPROM groups. The differences indicated higher levels of oxidative stress in amniotic tissues with FPROM and PPROM after downregulation of si-Nrf2 in HAE cells. Antioxidants were lower in amniotic tissues with the FPROM group and PPROM group than in the control group. The antioxidant enzymes catalase (CAT), glutathione (GSH), glutathione peroxidase (GSHPx), and superoxide dismutases (SOD1 and SOD2) were examined in amniotic tissues. We found that the ROS levels were significantly increased after downregulation of si-Nrf2 compared with the control group. We found that the expression of Heme Oxygenase-1 (HO-1) and Glycogen Synthase Kinase-3b (GSK-3b), which is critical in the Keap-1/Nrf2 signaling pathway, increased significantly after downregulation of si-Nrf2 in HAE cells.

Conclusions

We found that increased ROS levels and decreased antioxidant enzymes in the PPROM and FPROM patients compared with the control group.

Associations of maternal ambient temperature exposures during pregnancy with the risk of preterm birth and the effect modification of birth order during the new baby boom: A birth cohort study in Guangzhou, China

Maternal exposures to ambient temperatures during pregnancy may increase the preterm birth (PTB) risk; however, which periods have stronger effects remain controversial. The effects of temperature exposure on PTB in first- and second-born neonate groups may be different during the new baby boom that has followed the Two-child Policy in China. We examined a birth cohort of 4928 pregnant women beginning in 2016 in Guangzhou, China. An inverse distance weighted method was used to estimate the temperature exposure at each individual residential address. A distribution lag non-linear model incorporating a Cox proportional hazard model was employed to estimate the effects of temperature exposure on PTB and test the effects modification of birth order related to the new baby boom. A total of 4101 pregnant women were included, of which 234 (5.7%) experienced PTB. Compared with the mean temperature (23.0 °C), we found a significantly higher risks of PTB associated with high temperatures (i.e, 30 °C [95th centile]) from the 4th to 8th, and 22nd to 27th gestational weeks. A peak effect was found during the 6th week (HR = 1.79, 95% CI: 1.26, 2.54) and 24th week (HR = 1.83, 95% CI: 1.27, 2.62). The risks of PTB were reduced for low temperatures (i.e. 14 °C [5th centile] versus 23.0 °C) from the 2nd to 10th and 20th to 26th gestational weeks, and the negative peak effect was found during the 4th week (HR = 0.43, 95% CI: 0.26, 0.72) and 23rd week (HR = 0.59, 95% CI: 0.43, 0.83). Stratification analyses showed that significant effects of 30 °C versus 23 °C on PTB were observed during the 4th to 8th weeks in the second-born neonate, and the peak effect was found in the 6th week (HR = 2.13, 95% CI: 1.31, 3.47). However, we did not find significant effects of 30 °C during the same weeks in the first-born neonate group. Maternal exposures to higher temperatures during pregnancy may increase the risk of PTB, and lower temperatures may decrease the risk of PTB. Stronger effects of temperature exposures during the first trimester on PTB risk were found among the second-born neonates than among the first-born neonates.

Pregnancy vulnerability in urban areas: a pragmatic approach combining behavioral, medico-obstetrical, socio-economic and environmental factors

Multiple risk factors are associated with adverse pregnancy outcomes (APO), but how all these different factors combine and accumulate remains unknown. The objective of this observational retrospective study was to describe the accumulation of multiple vulnerability markers in pregnant women living in an urban area. Women living in Besançon (France) who delivered between 2005 and 2009 were included. Individual data were collected from the obstetrical records while environmental exposures were collected using environmental prediction models. The accumulation of 15 vulnerability markers, grouped into six dimensions (maternal age, smoking, body mass index (BMI), socio-economic, medico-obstetrical and environmental vulnerabilities) was described and analyzed in comparison with four APO. Among the 3686 included women, 20.8% were aged under 20 or over 34 and 21.9% had an extreme pre-pregnancy BMI. 18.8% declared smoking during pregnancy. Women exposed to socio-economic, medico-obstetrical or environmental vulnerability were 14.2%, 31.6% and 42.4% respectively. While 20.6% were not exposed to any marker, 18.8% accumulated three or more dimensions. The risk of APO increased significantly with the cumulative number of vulnerabilities. Define and validate a vulnerability score could be useful to identify vulnerable women, adapt their pregnancy monitoring and help policy makers to implement appropriate education or health promotion programs.

The Impact of Severe Maternal Morbidity on Very Preterm Infant Outcomes

OBJECTIVE

To estimate the prevalence of severe maternal morbidity among very preterm births and determine its association with very preterm infant mortality and morbidity.

STUDY DESIGN

This study used New York City Vital Statistics birth and death records linked with maternal and newborn discharge abstract data for live births between 2010 and 2014. We included 6901 infants without congenital anomalies born between 24^0/7 and 32^6/7 weeks of gestation. Severe maternal morbidity was identified as life-threatening conditions or life-saving procedures. Outcomes were first-year infant mortality, severe neonatal morbidity (bronchopulmonary dysplasia, severe necrotizing enterocolitis, stage 3-5 retinopathy of prematurity, and intraventricular hemorrhage grades 3-4), and a combined outcome of death or morbidity.

RESULTS

Twelve percent of very preterm live-born infants had a mother with severe maternal morbidity. Maternal and pregnancy characteristics associated with occurrence of severe maternal morbidity were multiparity, being non-Hispanic black, and preexisting health conditions, but gestational age and the percentage small for gestational age did not differ. Infants whose mothers experienced severe maternal morbidity had higher first-year mortality, 11.2% vs 7.7% without severe maternal morbidity, yielding a relative risk of 1.39 (95% CI: 1.14-1.70) after adjustment for maternal characteristics, preexisting comorbidities, pregnancy complications, and hospital factors. Severe neonatal morbidity was not associated with severe maternal morbidity.

CONCLUSIONS

Severe maternal morbidity is an independent risk factor for mortality in the first year of life among very preterm infants after consideration of other maternal and pregnancy risk factors.

Trends in maternal prepregnancy body mass index (BMI) and its association with birth and maternal outcomes in California, 2007-2016: A retrospective cohort study

OBJECTIVE

To determine recent trends in maternal prepregnancy body mass index (BMI) and to quantify its association with birth and maternal outcomes.

METHODS

A population-based retrospective cohort study included resident women with singleton births in the California Birth Statistical Master Files (BSMF) database from 2007 to 2016. There were 4,621,082 women included out of 5,054,968 women registered in the database. 433,886 (8.6%) women were excluded due to invalid or missing information for BMI. Exposures were underweight (BMI < 18.5 kg/m2), normal weight (18.5-24.9 kg/m2), overweight (25.0-29.9 kg/m2), and obese (≥ 30 kg/m2) at the onset of pregnancy. Obesity was subcategorized into class I (30.0-34.9 kg/m2), class II (35.0-39.9 kg/m2), and class III (≥ 40 kg/m2), while adverse outcomes examined were low birth weight (LBW), very low birth weight (VLBW), macrosomic births, preterm birth (PTB), very preterm birth (VPTB), small-for-gestational-age birth (SGA), large-for-gestational-age birth (LGA), and cesarean delivery (CD). Descriptive analysis, simple linear regression, and multivariate logistic regression were performed, and adjusted odds ratios (AORs) with 95% confidence intervals (CIs) for associations were estimated.

RESULTS

Over the ten-year study period, the prevalence of underweight and normal weight women at time of birth declined by 10.6% and 9.7%, respectively, while the prevalence of overweight and obese increased by 4.3% and 22.9%, respectively. VLBW increased significantly with increasing BMI, by 24% in overweight women and by 76% in women with class III obesity from 2007 to 2016. Women with class III obesity also had a significant increase in macrosomic birth (170%) and were more likely to deliver PTB (33%), VPTB (66%), LGA (231%), and CD (208%) than women with a normal BMI. However, obese women were less likely to have SGA infants; underweight women were 51% more likely to have SGA infants than women with a normal BMI.

CONCLUSIONS

In California from 2007 to 2016, there was a declining trend in women with prepregnancy normal weight, and a rising trend in overweight and obese women, particularly obesity class III. Both extremes of prepregnancy BMI were associated with an increased incidence of adverse neonatal outcomes; however, the worse outcomes were prominent in those women classified as obese.

Association between maternal pre-pregnancy obesity and preterm birth according to maternal age and race or ethnicity: a population-based study

BACKGROUND

The relation between maternal pre-pregnancy obesity and preterm birth is controversial and inconclusive. We aimed to clarify the association between pre-pregnancy obesity and preterm birth by maternal age and race or ethnicity in a large, multiracial, multiethnic, and diverse population in the USA.

METHODS

We did a population-based cohort study using nationwide birth certificate data from the US National Vital Statistics System for 2016 and 2017. We included all mothers who had a live singleton birth and who did not have pre-existing hypertension or diabetes. Pre-pregnancy obesity was defined as a pre-pregnancy BMI of at least 30 kg/m². Preterm birth was defined as gestational age of less than 37 weeks. We used logistic regression models adjusted for maternal age, race or ethnicity, parity, education levels, smoking during pregnancy, previous history of preterm birth, marital status, infant sex, and timing of initiation of prenatal care to estimate the odds ratio (OR) of preterm birth.

FINDINGS

We included 7 141 630 singleton livebirths in our analysis, 527 637 (7·4%) of which were preterm births. 127 611 (7·5%) Hispanic mothers, 244 578 (6·6%) non-Hispanic white mothers, and 102 509 (10·4%) non-Hispanic black mothers had preterm births. In the overall population, maternal pre-pregnancy obesity was significantly associated with an increased risk of preterm birth compared with maternal pre-pregnancy healthy weight (ie, BMI of 18·5-24·9 kg/m²; adjusted OR 1·18 [95% CI 1·18-1·19]). In non-Hispanic white women, maternal obesity was inversely associated with preterm birth among those younger than 20 years (adjusted OR 0·92 [95% CI 0·88-0·97]), but positively associated with preterm birth among those aged 20 years or older (1·04 [1·01-1·06], 1·20 [1·18-1·23], 1·34 [1·31-1·37], 1·40 [1·36-1·43], and 1·39 [1·31-1·46] among those aged 20-24 years, 25-29 years, 30-34 years, 35-39 years, and ≥40 years, respectively). In Hispanic women, maternal obesity was not associated with preterm birth among those younger than 20 years (0·98 [0·93-1·04]), but positively associated with preterm birth among those aged 20 years or older (1·06 [1·03-1·09], 1·21 [1·17-1·24], 1·32 [1·28-1·36], 1·38 [1·33-1·43], and 1·30 [1·22-1·40] among those aged 20-24 years, 25-29 years, 30-34 years, 35-39 years, and ≥40 years, respectively). In non-Hispanic black women, maternal obesity was inversely associated with preterm birth among those younger than 30 years (0·76 [0·71-0·81] in those <20 years, 0·83 [0·80-0·86] in those aged 20-24 years, and 0·98 [0·95-1·01] among those aged 25-29 years), but positively associated with preterm birth among those aged 30 years or older (1·15 [1·11-1·19], 1·26 [1·20-1·32], and 1·29 [1·18-1·42] among those aged 30-34 years, 35-39 years, and ≥40 years, respectively).

INTERPRETATION

Maternal pre-pregnancy obesity is significantly associated with the risk of preterm birth in the general population, but the risk differs according to maternal age and race or ethnicity. Future investigation is warranted to understand the underlying mechanisms.

FUNDING

US National Institutes of Health.

The relationship between maternal body mass index and pregnancy outcomes in twin compared with singleton pregnancies

OBJECIVE

Women with twins have an a priori increased risk for many of the complications associated with maternal obesity. Thus, the impact of maternal obesity in twins may differ from that reported in singletons. In addition, given the increased metabolic demands in twin pregnancies, the impact of maternal underweight may be greater in twin compared with singleton gestations. Our objective was to test the hypothesis that the relationship between maternal pre-pregnancy body mass index (BMI) and adverse pregnancy outcomes differ between twin and singleton gestations.

METHODS

This was a retrospective population-based study of all women who had a singleton or twin hospital birth in Ontario, Canada, between April 2012 and March 2016. Data were obtained from the Better Outcomes Registry & Network (BORN) Ontario. The relationship between maternal BMI category and pregnancy complications was assessed separately in twin and singleton gestations. The primary outcome was a composite variable that included any of the following complications: preeclampsia, gestational diabetes, or preterm birth before 32^0/7 weeks. Relative risk (aRR) and 95% confidence intervals (CI) for adverse outcomes for each BMI category as defined by WHO (using normal weight category as reference) were generated using modified Poisson regression, adjusting for maternal age, nulliparity, smoking, previous preterm birth, and fetal sex.

RESULTS

A total of 487,870 women with singleton (n = 480,010) and twin (n = 7860) pregnancies met the inclusion criteria. The risk of the composite primary outcome, preeclampsia, gestational diabetes, and cesarean delivery increased with high maternal BMI in both singleton and twin gestations, but these associations were weaker in twin compared with singleton gestations (association of BMI ≥ 40.0 kg/m² with primary outcome: aRR = 3.10, 95%-CI 2.96-3.24 in singletons compared with aRR = 1.74, 95%-CI 1.37-2.20 in twins). In singleton pregnancies the risk of preterm birth at < 32^0/7 weeks increased with maternal BMI, mainly due to an increased risk of provider-initiated preterm birth. In twin gestations, however, underweight (but not overweight or obesity) was associated with the greatest risk of preterm birth at < 32 weeks (aRR 1.67, 95%-CI 1.17-2.37), mainly due to an increased risk of spontaneous preterm birth (aRR 2.10, 95%-CI 1.44-3.08).

CONCLUSION

In healthy women with twin pregnancies, underweight is associated with the greatest risk for preterm birth, while the association of maternal obesity with adverse pregnancy outcomes is weaker than that observed in singletons.

Body mass index restrictions in fertility treatment: a national survey of OB/GYN subspecialists

PURPOSE

To explore the attitudes of reproductive endocrinology and infertility (REI) and maternal-fetal medicine (MFM) subspecialists regarding the necessity and appropriateness of body mass index (BMI) cutoffs for women seeking fertility treatment.

METHODS

Members of the Society for Reproductive Endocrinology and Infertility (SREI) and the Society for Maternal Fetal Medicine (SMFM) were invited to participate in a survey querying their knowledge of existing institutional or clinic BMI policies and personal opinions regarding upper and lower BMI cutoffs for a range of fertility treatments, including oral ovulation agents, gonadotropins, and in vitro fertilization.

RESULTS

Respondents included 398 MFMs and 201 REIs. The majority of REI and MFM providers agreed with upper limit BMI cutoffs (72.5% vs 68.2%, p = 0.29), but REIs were twice as likely to support lower limit BMI restrictions compared to MFMs (56.2% vs 28.4%, p < 0.0001). Those who supported upper BMI restrictions were more likely to be female and report existing institutional BMI cutoffs. The majority of respondents (99.3%) believed that an official statement to guide clinicians should be issued by a national professional organization.

CONCLUSIONS

Although practice patterns widely vary, the majority of REIs and MFMs believe that there should be a BMI cutoff above which women should not be offered immediate fertility treatment. Furthermore, there is a reported need for a written statement by a national professional organization to guide clinical practice and to ensure that OB/GYN subspecialists are providing consistent, fair, and safe recommendations to infertile women at the extremes of BMI.

Interpregnancy Body Mass Index Changes: Distribution and Impact on Adverse Pregnancy Outcomes in the Subsequent Pregnancy

OBJECTIVE

To examine the change in body mass index (BMI) categories between pregnancies and its effect on adverse pregnancy outcomes.

STUDY DESIGN

We performed a retrospective cohort study of women with two consecutive deliveries from 2005 to 2010. Analysis was limited to women with BMI recorded at <24 weeks for both pregnancies. Standard BMI categories were used. Adverse pregnancy outcomes included preterm birth at <37 weeks, intrauterine growth restriction (IUGR), pregnancy-related hypertension, and gestational diabetes mellitus (GDM). Women with increased BMI category between pregnancies were compared with those who remained in the same BMI category.

RESULTS

In total, 537 women were included, of whom 125 (23%) increased BMI category. There was no association between increase in BMI category and risk of preterm birth, IUGR, or pregnancy-related hypertension. Women who increased BMI category had an increased odds of GDM compared with women who remained in the same BMI category (6.4 vs. 2.2%; p = 0.018). The increased risk remained after controlling for age, history of GDM, and starting BMI (adjusted odds ratio: 8.2; 95% confidence interval: 2.1-32.7; p = 0.003).

CONCLUSION

Almost one-quarter of women increased BMI categories between pregnancies. This modifiable risk factor has a significant impact on the risk of GDM.

IUGR Is Associated With Marked Hyperphosphorylation of Decidual and Maternal Plasma IGFBP-1

CONTEXT

The mechanisms underpinning intrauterine growth restriction (IUGR), as a result of placental insufficiency, remain poorly understood, no specific treatment is available, and clinically useful biomarkers for early detection are lacking.

OBJECTIVE

We hypothesized that human IUGR is associated with inhibition of mechanistic target of rapamycin (mTOR) and activation of amino acid response (AAR) signaling, increased protein kinase casein kinase-2 (CK2) activity, and increased insulin-like growth factor-binding protein 1 (IGFBP-1) expression and phosphorylation in decidua and that maternal plasma IGFBP-1 hyperphosphorylation in the first trimester predicts later development of IUGR.

DESIGN, SETTING, AND PARTICIPANTS

Decidua [n = 16 appropriate-for-gestational age (AGA); n = 16 IUGR] and maternal plasma (n = 13 AGA; n = 13 IUGR) were collected at delivery from two different cohorts. In addition, maternal plasma was obtained in the late first trimester from a third cohort of women (n = 7) who later delivered an AGA or IUGR infant.

MAIN OUTCOME MEASURES

Total IGFBP-1 expression and phosphorylation (Ser101/Ser119/Ser169), mTOR, AAR, and CK2 activity in decidua and IGFBP-1 concentration and phosphorylation in maternal plasma.

RESULTS

We show that decidual IGFBP-1 expression and phosphorylation are increased, mTOR is markedly inhibited, and AAR and CK2 are activated in IUGR. Moreover, IGFBP-1 hyperphosphorylation in first-trimester maternal plasma is associated with the development of IUGR.

CONCLUSIONS

These data are consistent with the possibility that the decidua functions as a nutrient sensor linking limited oxygen and nutrient availability to increased IGFBP-1 phosphorylation, possibly mediated by mTOR and AAR signaling. IGFBP-1 hyperphosphorylation in first-trimester maternal plasma may serve as a predictive IUGR biomarker, allowing early intervention.

Maternal body mass index and risk of intraventricular hemorrhage in preterm infants

BackgroundIntraventricular hemorrhage (IVH) and pre-pregnancy obesity and underweight have been linked to inflammatory states. We hypothesize that IVH in preterm infants is associated with pre-pregnancy obesity and underweight due to an inflammatory intrauterine environment.MethodsPopulation-based study of infants born between 22 and 32 weeks' gestation from 2007 to 2011. Data were extracted from vital statistics and the California Perinatal Quality Care Collaborative. Results were examined for all cases (any IVH) and for severe IVH.ResultsAmong 20,927 infants, 4,818 (23%) had any IVH and 1,514 (7%) had severe IVH. After adjustment for confounders, there was an increased risk of IVH associated with pre-pregnancy obesity, relative risk 1.14 (95% confidence interval (CI) 1.06, 1.32) for any IVH, and 1.25 (85% CI 1.10, 1.42) for severe IVH. The direct effect of pre-pregnancy obesity on any IVH was significant (P<0.001) after controlling for antenatal inflammation-related conditions, but was not significant after controlling for gestational age (P=0.56).ConclusionPre-pregnancy obesity was found to be a risk factor for IVH in preterm infants; however, this relationship appeared to be largely mediated through the effect of BMI on gestational age at delivery. The etiology of IVH is complex and it is important to understand the contributing maternal factors.

Are risk factors for preterm and early-term live singleton birth the same? A population-based study in France

OBJECTIVES

To investigate whether risk factors for preterm (<37 weeks gestation) and early-term birth (37 and 38 weeks gestation) are similar.

DESIGN

Nationally representative cross-sectional study of births.

SETTING

France in 2010.

PARTICIPANTS

Live singleton births (n=14 326).

PRIMARY AND SECONDARY OUTCOME MEASURES

Preterm and early-term birth rates overall and by mode of delivery (spontaneous and indicated). Risk factors were maternal sociodemographic characteristics, previous preterm birth, height, prepregnancy body mass index (BMI) and smoking, assessed using multinomial regression models with full-term births 39 weeks and over as the reference group.

RESULTS

There were 5.5% preterm and 22.5% early-term births. Common risk factors were: a previous preterm delivery (adjusted relative risk ratio (aRRR) 8.2 (95% CI 6.2 to 10.7) and aRRR 2.4 (95% CI 2.0 to 3.0), respectively), short stature, underweight (overall and in spontaneous deliveries), obesity (in indicated deliveries only), a low educational level and Sub-Saharan African origin. In contrast, primiparity was a risk factor only for preterm birth, aRRR 1.8 (95% CI 1.5 to 2.2), while higher parity was associated with greater risk of early-term birth.

CONCLUSIONS

Most population-level risk factors were common to both preterm and early-term birth with the exception of primiparity, and BMI which differed by mode of onset of delivery. Our results suggest that preterm and early-term birth share similar aetiologies and thus potentially common strategies for prevention.

Maternal obesity is associated with chorioamnionitis and earlier indicated preterm delivery among expectantly managed women with preterm premature rupture of membranes

OBJECTIVE

To determine the association between maternal obesity and delivery due to chorioamnionitis prior to labor onset, among expectantly managed women with preterm premature rupture of membranes (pPROM).

METHODS

This was a secondary analysis of a multicenter randomized trial of magnesium sulfate versus placebo to prevent cerebral palsy or death among offspring of women with anticipated delivery at 24-31-week gestation. After univariable analysis, Cox proportional hazard evaluated the association between maternal obesity and chorioamnionitis, while Laplace regression investigated how obesity affects the gestational age at delivery of the first 20% of women developing the outcome of interest.

RESULTS

A total of 164 of the 1942 women with pPROM developed chorioamnionitis prior to labor onset. Obese women had a 60% increased hazard of developing such complication (adjusted HR 1.6, 95%CI 1.1-2.1, p = .008), prompting delivery 1.5 weeks earlier, as the 20th survival percentile was 27.2-week gestation (95%CI 26-28.6) among obese as opposed to 28.8 weeks (95%CI 27.4-30.1) (p = .002) among nonobese women.

CONCLUSIONS

Maternal obesity is a risk factor for chorioamnionitis prior to labor onset. Future studies will determine if obesity is important enough to change the management of latency after pPROM according to maternal BMI.

Short interpregnancy interval increases the risk of preterm premature rupture of membranes and early delivery

OBJECTIVES

Preterm premature rupture of membranes (PPROM) is a major contributor to overall preterm birth (PTB) rates. A short interpregnancy interval (IPI) is a well-known risk factor for PTB. It is unknown if a short IPI specifically affects the risk of developing PPROM in a subsequent pregnancy. We sought to determine the association between IPI and the risk of PPROM in a subsequent pregnancy.

METHODS

A retrospective cohort study using the Missouri birth certificate database of singleton births from 2003 to 2013 was conducted. A short IPI (delivery of the prior pregnancy to conception of the index pregnancy) was defined as ≤6 months. IPI >6 months was categorized into two groups: IPI 7-23 months and IPI ≥24 months. PPROM was defined as premature rupture of membranes between 16⁰ and 36⁶ weeks. Multivariable logistic regression was conducted to determine the association between IPI and PPROM while controlling for maternal age, race, body mass index (BMI), education level, use of social services (Medicaid insurance, food stamps, or participation in the WIC [Women, Infants, and Children] program), tobacco use, and history of PTB. Secondary outcome included the gestational age at delivery, categorized into five subgroups (≤24⁰, 24¹-28⁰, 28¹-32⁰, 32¹-34⁰, and 34¹-36⁶ weeks).

RESULTS

474,957 subjects with singleton gestations had data available to calculate the IPI. Of these, 1.4% (n = 6797) experienced PPROM. IPI ≤6 months was significantly associated with an increased risk of developing PPROM compared with patients with IPI ≥24 months (odds ratio (OR) 1.80, 95% CI 1.70-1.90, p < .001). A higher proportion of women with IPI ≤6 months delivered between 28¹ and 32⁰ weeks compared to the other two IPI groups (27.0 versus 15.0 and 16.4%, p < .001). Individual maternal factors associated with an increased risk of PPROM included advanced maternal age, African American race, BMI <18.5 kg/m², BMI ≥30 kg/m², use of social services, tobacco use, and a prior PTB.

CONCLUSION

Our data demonstrate that an IPI of ≤6 months is significantly associated with an increased risk of developing PPROM in the subsequent pregnancy. Of greater clinical relevance is that these women were more likely to deliver between 28¹ and 32⁰ weeks as compared with women with a longer IPI. Novel to this study is the establishment of a specific link between a short IPI and PPROM with subsequent early delivery. Several maternal demographic factors known to be associated with PTB risk were also found to be associated with an increased risk of PPROM. Further studies are necessary to elucidate plausible biologic mechanisms ultimately leading to the development and implementation of preventive and therapeutic strategies for this high-risk cohort.

What factors are related to recurrent preterm birth among underweight women?. J Matern Fetal Neonatal Med 2017;31:560-566. [PMID: 28166677 DOI: 10.1080/14767058.2017.1292243]

OBJECTIVE

Our objective was to identify factors associated with recurrent preterm birth among underweight women.

METHODS

Maternally linked hospital and birth certificate records of deliveries in California between 2007 and 2010 were used. Consecutive singleton pregnancies of women with underweight body mass index (BMI <18.5 kg/m²) in the first pregnancy were analyzed. Pregnancies were categorized based on outcome of the first and second birth as: term-term; term-preterm; preterm-term and preterm-preterm.

RESULTS

We analyzed 4971 women with underweight BMI in the first pregnancy. Of these, 670 had at least one preterm birth. Among these 670, 86 (21.8%) women experienced a recurrent preterm birth. Odds for first term - second preterm birth were decreased for increases in maternal age (aOR: 0.90, 95%CI: 0.95-0.99) whereas inter-pregnancy interval <6 months was related to both first term - second preterm birth (aOR:1.66, 95%CI: 1.21-2.28) and first preterm birth - second term birth (aOR: 1.43, 95%CI: 1.04-1.96). Factors associated with recurrent preterm birth were: negative or no change in pre-pregnancy weight between pregnancies (aOR: 1.67, 95%CI: 1.07-2.60), inter-pregnancy interval <6 months (aOR: 2.14, 95%CI: 1.29-3.56), and maternal age in the first pregnancy (aOR: 0.93, 95%CI: 0.90-0.97).

CONCLUSIONS

Recurrent preterm birth among underweight women was associated with younger age, short inter-pregnancy interval, and negative or no weight change between pregnancies.

Extremities of body mass index and their association with pregnancy outcomes in women undergoing in vitro fertilization in the United States

OBJECTIVE

To investigate the associations among underweight body mass index (BMI), pregnancy, and obstetric outcomes among women using assisted reproductive technology (ART).

DESIGN

Retrospective cohort study using national data and log binomial regression.

SETTING

Not applicable.

PATIENT(S)

Women undergoing IVF in the United States from 2008 to 2013.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Pregnancy outcomes (intrauterine pregnancy, live birth rates) per transfer, miscarriage rate per pregnancy, and low birth weight and preterm delivery rates among singleton and twin pregnancies.

RESULT(S)

For all fresh autologous in vitro fertilization (IVF) cycles in the United States from 2008 to 2013 (n = 494,097 cycles, n = 402,742 transfers, n = 180,855 pregnancies) reported to the national ART Surveillance System, compared with normal weight women, underweight women had a statistically significant decreased chance of intrauterine pregnancy (adjusted risk ratio [aRR] 0.97; 95% confidence interval [CI], 0.96-0.99) and live birth (aRR 0.95; 95% CI, 0.93-0.98) per transfer. Obese women also had a statistically decreased likelihood of both (aRR 0.94; 95% CI, 0.94-0.95; aRR 0.87; 95% CI, 0.86-0.88, respectively). Among cycles resulting in singleton pregnancy, both underweight and obese statuses were associated with increased risk of low birth weight (aRR 1.39; 95% CI, 1.25-1.54, aRR 1.26; 95% CI, 1.20-1.33, respectively) and preterm delivery (aRR 1.12; 95% CI, 1.01-1.23, aRR 1.42; 95% CI, 1.36-1.48, respectively). The association between underweight status and miscarriage was not statistically significant (aRR 1.04; 95% CI, 0.98-1.11). In contrast, obesity was associated with a statistically significantly increased miscarriage risk (aRR 1.23; 95% CI, 1.20-1.26).

CONCLUSION(S)

Among women undergoing IVF, prepregnancy BMI affects pregnancy and obstetric outcomes. Underweight status may have a limited impact on pregnancy and live-birth rates, but it is associated with increased preterm and low-birth-weight delivery risk. Obesity negatively impacts all ART and obstetric outcomes investigated.

[Association between maternal pre-pregnancy body mass index and adverse outcomes of late preterm infants]

OBJECTIVE

To study the association between maternal pre-pregnancy body mass index (BMI) and adverse outcomes of late preterm infants (LPI).

METHODS

A total of 367 LPI who were born from January 2011 to December 2015 and admitted to the neonatal ward were enrolled. The BMI criteria for Chinese population were used to analyze the factors for maternal pre-pregnancy BMI and its association with adverse outcomes of LPI (1 minute Apgar score ≤7, delivery room resuscitation, hospitalization days after birth >7 days, and ventilation duration ≥6 hours).

RESULTS

Of all LPIs, there were 64 LPI (17.4%) in the low maternal pre-pregnancy BMI group, 243 LPI (66.2%) in the normal maternal pre-pregnancy BMI group, and 60 LPI (16.4%) in the high maternal pre-pregnancy BMI group. Low pre-pregnancy BMI was the risk factor for 1 minute Apgar score ≤7 (OR=3.243, 95% CI: 1.102-9.546) and need for delivery room resuscitation (OR=3.492, 95%CI: 1.090-11.190), and high pre-pregnancy BMI was the risk factor for hospitalization days after birth >7 days (OR=1.992, 95%CI: 1.024-3.874).

CONCLUSIONS

Abnormal maternal pre-pregnancy BMI has adverse effects on the outcomes of LPI. In order to reduce these adverse outcomes BMI should be controlled within the normal range in pregnant women.

Prevention of preterm delivery: current challenges and future prospects

Preterm birth (PTB), defined as delivery at <37 weeks of gestation, is the most important cause of neonatal morbidity and mortality. Therefore, preventing PTB is one of the main goals in obstetric care. In this review, we provide an overview of the current available literature on screening for risk factors for PTB and a summary of preventive strategies in both low-risk and high-risk women with singleton or multiple gestations. Furthermore, current challenges and future prospects on PTB are discussed. For an optimal prevention of PTB, risk stratification should be based on a combination of (maternal) risk factors, obstetric history, and screening tools. Cervical length measurements can help identify women at risk. Thereafter, preventive strategies such as progesterone, pessaries, and cerclage may help prevent PTB. Effective screening and prevention of PTB vary between the different pregnancy populations. In singleton or multiple pregnancies with a short cervix, without previous PTB, a pessary or progesterone might prevent PTB. In women with a (recurrent) PTB in the past, progesterone and a cerclage may prevent recurrence. The effect of a pessary in these high-risk women is currently being studied. A strong collaboration between doctors, patients' organizations, pharmaceutical companies, and (international) governments is needed to reduce the morbidity and mortality as a result of spontaneous PTB.

Pregnancy complications in spontaneous and assisted conceptions of women with infertility and subfertility factors. A comprehensive review

In the literature, there is growing evidence that assisted reproductive techniques increase the risk of pregnancy complications in subfertile couples. Moreover, many concomitant preconception risk factors for subfertility are frequently present in the same subject and increase the risk of pregnancy complications. This review aimed to summarize in a systematic fashion the best current evidence regarding the effects of preconception maternal factors on maternal and neonatal outcomes. A literature search up to March 2016 was performed in IBSS, SocINDEX, Institute for Scientific Information, PubMed, Web of Science and Google Scholar. An evidence-based hierarchy was used to determine which articles to include and analyse. Available data show that the risk of pregnancy complications in spontaneous and assisted conceptions is likely multifactorial, and the magnitude of this risk is probably very different according specific subgroups of patients. Notwithstanding the only moderate level and quality of the available evidence, available data suggest that the presence and the treatment of specific preconception cofactors of subfertility should be always taken into account both in clinical practice and for scientific purposes.

Women's prepregnancy underweight as a risk factor for preterm birth: a retrospective study

OBJECTIVE

To investigate the distribution of known factors for preterm birth (PTB) by severity of maternal underweight; to investigate the risk-adjusted relation between severity of underweight and PTB, and to assess whether the relation differed by gestational age.

DESIGN

Retrospective cohort study.

SETTING

State of California, USA.

METHODS

Maternally linked hospital and birth certificate records of 950 356 California deliveries in 2007-2010 were analysed. Singleton live births of women whose prepregnancy body mass index (BMI) was underweight (<18.5 kg/m² ) or normal (18.50-24.99 kg/m² ) were analysed. Underweight BMI was further categorised as: severe (<16.00), moderate (16.00-16.99) or mild (17.00-18.49). PTB was grouped as 22-27, 28-31, 32-36 or <37 weeks (compared with 37-41 weeks). Adjusted multivariable Poisson regression modeling was used to estimate relative risk for PTB.

MAIN OUTCOME MEASURES

Risk of PTB.

RESULTS

About 72 686 (7.6%) women were underweight. Increasing severity of underweight was associated with increasing percent PTB: 7.8% (n = 4421) in mild, 9.0% (n = 1001) in moderate and 10.2% (475) in severe underweight. The adjusted relative risk of PTB also significantly increased: adjusted relative risk (aRR) = 1.22 (95% CI 1.19-1.26) in mild, aRR = 1.41 (95% CI 1.32-1.50) in moderate and aRR = 1.61 (95% CI 1.47-1.76) in severe underweight. These findings were similar in spontaneous PTB, medically indicated PTB, and the gestational age groupings.

CONCLUSION

Increasing severity of maternal prepregnancy underweight BMI was associated with increasing risk-adjusted PTB at <37 weeks. This increasing risk was of similar magnitude in spontaneous and medically indicated births and in preterm delivery at 28-31 and at 32-36 weeks of gestation.

TWEETABLE ABSTRACT

Increasing severity of maternal underweight BMI was associated with increasing risk of preterm birth.

Effect of obesity on neonatal outcomes in pregnancies with preterm premature rupture of membranes

BACKGROUND

Maternal obesity is associated with increased systemic inflammation and an increased risk of preterm premature rupture of membranes. There is an established association between an inflammatory intrauterine environment and adverse neonatal outcomes that is independent of gestational age and mediated by the fetal inflammatory response. It is unknown whether the maternal systemic inflammation that is present in obese women influences the intrauterine environment and predisposes the fetus to adverse neonatal outcomes after preterm premature rupture of membranes.

OBJECTIVE

The purpose of this study was to determine whether maternal obesity is associated with adverse neonatal outcomes in pregnancies that are complicated by preterm premature rupture of membranes.

STUDY DESIGN

This was a secondary analysis of the Maternal-Fetal Medicine Units Network Randomized Clinical Trial on the Beneficial Effects of Antenatal Magnesium Sulfate. Women with singleton pregnancies that were affected by preterm premature rupture of membranes who delivered live-born infants between 24 + 0 and 33 + 6 weeks of gestation were included. An adverse neonatal outcome was defined as a composite outcome of neonatal death, severe necrotizing enterocolitis, respiratory distress syndrome, sepsis, or severe intraventricular hemorrhage. The rates of the composite outcome were compared between obese (body mass index, ≥30 kg/m(2)) and nonobese women. Multivariable logistic regression was used to evaluate the independent effect of obesity on neonatal outcomes. Magnesium sulfate administration, steroid administration, maternal diabetes mellitus, gestational age at delivery, indomethacin exposure, birthweight, and chorioamnionitis were all considered as possible covariates in the multivariable regression models.

RESULTS

Three hundred twenty-five of the 1288 women (25.2%) who were included were obese, and 202 of these women (62.2%) had neonates with adverse outcomes. In univariable analysis, maternal prepregnancy obesity was associated with increased odds of an adverse neonatal outcome (odds ratio, 0.30, 95% confidence interval, 1.00-1.68). However, in our multivariable logistic regression model, gestational age at delivery (odds ratio, 0.93, 95% confidence interval, 0.92-0.94 per day), but not maternal obesity (odds ratio, 1.02, 95% confidence interval, 0.75-1.38), was associated with adverse neonatal outcomes. Obese African American women experienced preterm premature rupture of membranes (189 vs 196 days; p < .001) and delivery (199 vs 205 days; p < .001) earlier than nonobese African American women. This difference was not seen in non-African American women.

CONCLUSIONS

Maternal obesity was not associated independently with adverse neonatal outcomes in pregnancies that were affected by preterm premature rupture of membranes after adjustment for gestational age at birth. However, obese African American women rupture and deliver earlier than other women, which causes increased neonatal morbidity.

Parturition dysfunction in obesity: time to target the pathobiology

Over a third of women of childbearing age in the United States are obese, and during pregnancy they are at increased risk for delayed labor onset and slow labor progress that often results in unplanned cesarean delivery. The biology behind this dysfunctional parturition is not well understood. Studies of obesity-induced changes in parturition physiology may facilitate approaches to optimize labor in obese women. In this review, we summarize known and proposed biologic effects of obesity on labor preparation, contraction/synchronization, and endurance, drawing on both clinical observation and experimental data. We present evidence from human and animal studies of interactions between obesity and parturition signaling in all elements of the birth process, including: delayed cervical ripening, prostaglandin insensitivity, amniotic membrane strengthening, decreased myometrial oxytocin receptor expression, decreased myocyte action potential initiation and contractility, decreased myocyte gap junction formation, and impaired myocyte neutralization of reactive oxygen species. We found convincing clinical data on the effect of obesity on labor initiation and successful delivery, but few studies on the underlying pathobiology. We suggest research opportunities and therapeutic interventions based on plausible biologic mechanisms.

Folic acid supplementation, preconception body mass index, and preterm delivery: findings from the preconception cohort data in a Chinese rural population

BACKGROUND

Folic acid (FA) supplementation before and during the first trimester can reduce the risk of occurrence of preterm delivery (PTD). Preconception body mass index (BMI) is also associated with PTD. This study aimed to investigate the combined effect of FA supplements and preconception BMI on the risk of PTD.

METHODS

The data of a cohort from 2010-2011 that was obtained through a preconception care service in China was used (including 172,206 women). A multivariable regression model was used to investigate the association between maternal preconception conditions and the risk of PTD. The interaction of preconception BMI and FA supplementation was measured by a logistic regression model.

RESULTS

Taking FA supplements in the preconception period or in the first trimester reduced the risk of PTD (odds ratio [OR] = 0.58 and OR = 0.61, respectively). Women with an abnormal BMI had an increased risk of PTD (OR = 1.09, OR = 1.10, and OR = 1.17 for underweight, overweight, and obese, respectively). Preconception BMI showed an interaction with the protective effect of FA supplementation for PTD. With regard to the interaction of FA supplementation, the adjusted odds ratio (aOR) was 0.57 (95% CI: 0.51, 0.64) in underweight women, 0.85 (95% CI: 0.73, 0.98) in overweight women, and 0.77 (95% CI, 0.65, 0.91) in obese women. Preconception BMI also showed an interaction with the time of FA supplementation. Women with a normal BMI who began to take FA supplements in the preconception period had the lowest risk of PTD (aORs: 0.58 vs. 0.65 beginning in the first trimester). The aORs at preconception and the first trimester in the underweight group were 0.56 vs. 0.60. The aORs at preconception and the first trimester were 0.94 vs. 0.65 and 1.15 vs. 0.60 in the overweight and obesity groups, respectively.

CONCLUSIONS

In our study, FA supplements reduced the risk of PTD, while abnormal BMI raised the risk of PTD, although higher BMI categories did not have this higher risk once adjusted analysis was conducted. The protective effect of FA supplementation for PTD was reduced in women with overweight or obesity. To get better protection of FA supplementation, women with normal BMI or underweight should begin to use in preconception, while women with overweight or obesity should begin to use after conception.

What contributes to disparities in the preterm birth rate in European countries?

PURPOSE OF REVIEW

In countries with comparable levels of development and healthcare systems, preterm birth rates vary markedly--a range from 5 to 10% among live births in Europe. This review seeks to identify the most likely sources of heterogeneity in preterm birth rates, which could explain differences between European countries.

RECENT FINDINGS

Multiple risk factors impact on preterm birth. Recent studies reported on measurement issues, population characteristics, reproductive health policies as well as medical practices, including those related to subfertility treatments and indicated deliveries, which affect preterm birth rates and trends in high-income countries. We showed wide variation in population characteristics, including multiple pregnancies, maternal age, BMI, smoking, and percentage of migrants in European countries.

SUMMARY

Many potentially modifiable population factors (BMI, smoking, and environmental exposures) as well as health system factors (practices related to indicated preterm deliveries) play a role in determining preterm birth risk. More knowledge about how these factors contribute to low and stable preterm birth rates in some countries is needed for shaping future policy. It is also important to clarify the potential contribution of artifactual differences owing to measurement.