Pre-pregnancy body mass index range and prevalence of hypertensive disorders of pregnancy: the Japan environment and children's study.

BACKGROUND

No consensus has been established for the optimal pre-pregnancy body mass index (BMI) required to reduce the incidence of hypertensive disorders of pregnancy (HDP) in Japanese women. This study investigated the association between the pre-pregnancy BMI range and the prevalence of HDP.

METHODS

Data from 96,796 women with singleton pregnancies at ≥ 22 weeks of gestation from the Japan Environment and Children's Study (enrolled between 2011 and 2014)-a nationwide birth cohort study-were analyzed. The participants were categorized according to pre-pregnancy BMI, as follows: ≤ 16.00, 16.01-17.00, 17.01-18.00, 18.01-19.00, 19.01-20.00, 20.01-21.00, 21.01-22.00, 22.01-23.00, 23.01-24.00, 24.01-25.00, 25.01-26.00, 26.01-27.00, 27.01-28.00, 28.01-29.00, 29.01-30.00, and > 30.00 kg/m2. Odds ratios (ORs) for HDP were calculated using multivariable regression analysis in each group, with the pre-pregnancy BMI 20.01-21.00 kg/m2 group as the reference group, adjusted for maternal characteristics, followed by the Bonferroni correction. Pre-pregnancy BMI cut-off value for predicting the incidence of HDP was calculated through a receiver operating characteristic (ROC) curve analysis.

RESULTS

The median pre-pregnancy BMI was 20.52 kg/m2 (interquartile range: 19.07‒22.48 kg/m2). Adjusted ORs for HDP and severe HDP increased significantly in women with pre-pregnancy BMI > 22.00 kg/m2, and in those with pre-pregnancy BMI of 24.01-25.00 kg/m2 and BMI > 26.00 kg/m2, respectively. No changes were observed in those with pre-pregnancy BMI ≤ 20.00 kg/m2. A pre-pregnancy BMI cut-off value of 22.31 kg/m2 and 22.37 kg/m2 predicted HDP and severe HDP with Youden's index (sensitivity: 47.1% and 44.0%, specificity: 73.9% and 74.2%) with AUC of 0.63 and 0.62, respectively. Another cut-off value of 32.47 kg/m2 and 32.89 kg/m2 was identified for predicting HDP and severe HDP, respectively, with a specificity > 99%. A similar trend was observed when the analysis was restricted to individuals of Japanese nationality only.

CONCLUSIONS

Pre-pregnancy BMI > 22.00 kg/m2 was associated with an increased prevalence of HDP compared with the pre-pregnancy BMI 20.01-21.00 kg/m2. Due to the low AUC, we propose that the cut-off BMI values for predicting the incidence of HDP may be used as a supplementary data to identify high-risk populations.