Interpregnancy weight change: associations with severe maternal morbidity and neonatal outcomes.

Background: Prepregnancy body mass index and gestational weight gain have been linked with severe maternal morbidity, suggesting that weight change between pregnancies may also play a role, as it does for neonatal outcomes.

Objective: This study assessed the association of changes in prepregnancy body mass index between 2 consecutive singleton pregnancies with the outcomes of severe maternal morbidity, stillbirth, and small- and large-for-gestational-age infants in the subsequent pregnancy.

Study Design: This observational study was based on birth records from 1,111,032 consecutive pregnancies linked to hospital discharge records in California (2007-2017). Interpregnancy body mass index change between the beginning of an index pregnancy and the beginning of the subsequent pregnancy was calculated from self-reported weight and height. Severe maternal morbidity was defined based on the Centers for Disease Control and Prevention index, including and excluding transfusion-only cases. We used multivariable log-binomial regression models to estimate adjusted risks, overall and stratified by prepregnancy body mass index at index birth.

Results: Substantial interpregnancy body mass index gain (≥4 kg/m) was associated with severe maternal morbidity in crude but not adjusted analyses. Substantial interpregnancy body mass index loss (>2 kg/m) was associated with increased risk of severe maternal morbidity (adjusted relative risk, 1.13; 95% confidence interval (1.07-1.19), and both substantial loss (adjusted relative risk, 1.11 [1.02-1.19]) and gain (≥4 kg/m; adjusted relative risk, 1.09 [1.02-1.17]) were associated with nontransfusion severe maternal morbidity. Substantial loss (adjusted relative risk, 1.17 [1.05-1.31]) and gain (1.26 [1.14-1.40]) were associated with stillbirth. Body mass index gain was positively associated with large-for-gestational-age infants and inversely associated with small-for-gestational-age infants.

Conclusion: Substantial interpregnancy body mass index changes were associated with modestly increased risk of severe maternal morbidity, stillbirth, and small- and large-for-gestational-age infants.