(473) Change in BMI Category: Impact on Maternal and Neonatal Outcomes

Objective: Pre-pregnancy BMI is a risk factor for the development of hypertensive disorders of pregnancy (PIH). However, the association between weight gain during pregnancy and the development of hypertensive disorders is understudied. The objective was to determine if change in BMI category change (eg overweight to class I obesity) was associated with development of PIH. Secondary outcomes were maternal composite outcome and fetal composite outcome.

Study Design: This was a retrospective cohort study performed using data from the National Vital Statistics Database of individuals with singleton, non-anomalous neonates from 2016-2020. Pregnancies with multiple gestations, anomalous neonates, pre-gestational diabetes, or chronic hypertension were excluded. Demographic and obstetrical variables were recorded. Groups were determined as no change in BMI (Group 1) or change in BMI (Group 2) from pre-pregnancy to delivery. Differences between groups were examined using chi-square or Fisher’s exact test. Multivariate regression models were used to calculate adjusted relative risk (aRR) with 95% confidence intervals (CI).

Results: A total of 19,718,555 pregnancies met inclusion criteria and 15,426,805 (78%) pregnancies were noted to have a change in BMI category. The overall rate of PIH was 6.6%. After multivariable adjustment, there was a significant difference in the rate of PIH. Compared to individuals in Group 1, individuals with a Group 2 were more likely to develop PIH (aRR of 1.39 (95% CI [1.38-1.39], p< 0.001). In the secondary outcome analysis, Group 2 compared to Group 1 had higher rates of maternal composite outcome (aRR 1.11, CI [1.11-1.11, p< 0.001]) and fetal composite outcome (aRR 1.37, CI [1.37-1.38], p< 0.001).

Conclusion: There was a significant association between change to a higher BMI category and development of PIH along with an increase in composite adverse maternal and fetal outcomes. Future studies are required to further delineate risks for patients whose delivery BMI changes to class III obesity as well as stratified risks for women with pre-pregnancy class IV obesity and above.