Impact of maternal body mass index on outcomes of singleton pregnancies after assisted reproductive technology: a 14-year analysis of the US Nationwide Inpatient Sample

The mediating role of pregnancy-induced hypertension on pre-pregnancy body mass index and adverse neonatal outcomes in women with assisted reproductive technology

OBJECTIVE

To explore whether pregnancy-induced hypertension (PIH) mediates the association between pre-pregnancy body mass index (BMI) and adverse neonatal outcomes in women undergoing assisted reproductive technology (ART) for singleton pregnancies.

METHODS

This cohort study collected 79437 maternal data from the National Vital Statistics System (NVSS) between 2020 and 2021. Univariable and multivariable logistic regression models were applied to estimate the association between pre-pregnancy BMI and PIH in women receiving ART as well as the associations between pre-pregnancy BMI and PIH and adverse neonatal outcomes. The mediation effect of PIH on the association between pre-pregnancy BMI and adverse neonatal outcomes was estimated according to the total effect, natural direct effect, natural indirect effect, and percentage of mediation.

RESULTS

There were 25769 participants had adverse neonatal outcomes at the end of the follow-up. After adjusting for confounding factors, an increased risk of PIH in women receiving ART was identified in those with pre-pregnancy BMI ≥25 kg/m2 [odds ratio (OR)=1.92, 95% confidence interval (CI):1.84-2.01]. Pre-pregnancy BMI ≥25 kg/m2 was associated with an increased risk of adverse neonatal outcomes (OR = 1.26, 95%CI:1.22-1.30). Women with PIH had an increased risk of adverse neonatal outcomes (OR = 1.79, 95%CI:1.71-1.87). The percentage mediated by PIH in the association between pre-pregnancy BMI and adverse neonatal outcomes was 21.30%.

CONCLUSION

PIH partially mediated the association between pre-pregnancy BMI and adverse neonatal outcomes in women receiving ART, which recommends that women control weight before receiving ART.

Pre-gravid body mass index is associated with a higher risk of gestational hypertension in singleton pregnancy following frozen-thawed embryo transfer

Introduction

Although it is well-known that obesity increases the risk of gestational hypertension (GH) in both spontaneous and assisted reproductive technology (ART) pregnancies. Recent data show that, in ART pregnancies, frozen-thawed embryo transfer (FET) is associated with an even higher risk of GH compared with fresh transfer. However, the relationship between pre-gravid body mass index (BMI) and GH in FET pregnancies has seldom been reported.

Objective

The aim of this study is to examine the effect of pre-gravid BMI on GH in singleton pregnancy following FET.

Methods

A retrospective cohort study at a tertiary hospital, including a total of 7,502 women who achieved singleton pregnancy after FET, was included. All patients were enrolled only once. On the basis of the BMI definitions of the Working Group on Obesity in China (WGOC) and the World Health Organization, the women were divided into normal BMI, overweight, and obese groups. The main outcome was GH, and the effect of pre-pregnancy BMI on GH was assessed by generalized linear model.

Results

The risk of GH in our study population was 6.15%. According to the BMI definitions of the WGOC, the risk of GH in the obese group (15.55%) was significantly higher than that of the overweight group (8.26%, P < 0.001) and the normal BMI group (4.68%, P < 0.001). Pre-gravid overweight and obesity were associated with higher GH risk (OR, 1.77; 95% CI, 1.41-2.20; P < 0.001; OR, 3.69; 95% CI, 2.77-4.91; P < 0.001). A non-linear relationship between pre-gravid BMI and GH was observed. The risk of GH decreased with pre-gravid BMI level up to the turning point of BMI = 28.6 kg/m2 (OR, 1.16; 95% CI, 1.12-1.21; P < 0.001).

Conclusion

Pre-gravid overweight and obesity are associated with higher GH risk among singleton pregnancy following FET. Before the turning point of BMI = 26.8 kg/m2, the risk of GH may increase 16.4% with each one-unit increment of maternal BMI. Women preparing for FET should maintain a normal BMI to lower the chances of GH.