Impact of Prepregnancy Body Mass Index in Low-Risk Pregnancies with Adequate Gestational Weight Gain: Trend and Adverse Outcomes.

OBJECTIVE

To examine the temporal trend of prepregnancy body mass index (BMI) and the association between prepregnancy BMI and adverse outcomes in low-risk pregnancies with adequate gestational weight gain (GWG).

STUDY

DESIGN

We conducted a retrospective cohort study using U.S. vital statistics data (2016-2023). We included low-risk pregnancies with adequate GWG that delivered nonanomalous, singleton live births at 37 to 41 weeks of gestation in a hospital; those with diabetes or hypertensive disorders were excluded. The exposure variable was prepregnancy BMI. Adverse outcomes were examined. The average annual percent change (AAPC) was calculated to assess the trend of prepregnancy BMI. Multivariable Poisson regression models with robust error variance were used to examine the association. Adjusted relative risks (aRR) with 95% confidence intervals (CI) were calculated.

RESULTS

Of 29,972,027 live births during the study period, 6,741,787 (22.5%) were included; among them, prepregnancy BMI distribution was as follows: 4.4% underweight, 52.9% normal weight, 23.3% overweight, and 19.4% obese. Over the 8 years, there was a significantly increased trend in the prevalence of maternal prepregnancy overweight (AAPC = 2.6; 95% CI: 2.1-3.2) and obesity (AAPC = 3.6; 95% CI: 2.9-4.4) in low-risk pregnancies with adequate GWG. Compared with women with prepregnancy normal weight, those with prepregnancy obesity were associated with a higher risk of primary cesarean delivery (aRR = 1.57, 95% CI = 1.56-1.58). Importantly, those with prepregnancy obesity class III were associated with the highest risk of primary cesarean delivery (aRR = 2.01, 95% CI = 1.99-2.02). Similar results were also noted in 5-minute Apgar < 5, assisted ventilation > 6 hours, neonatal seizure, neonatal ICU, neonatal death, and infant death.

CONCLUSION

Among low-risk pregnancies with adequate GWG, there was an upward trend in prepregnancy overweight and obesity from 2016 to 2023. The risks of adverse outcomes were the highest among pregnancies with prepregnancy obesity, especially with class III obesity.

KEY POINTS: · In 6.7 million low-risk pregnancies with adequate GWG, 19.4% were obese prior to pregnancy.. · During 2016 to 2023, the trend of prepregnancy obesity increased.. · Adverse outcomes were the highest in pregnancies with class III obesity..