Background: Few studies have examined secular trends in gestational weight gain (GWG) and findings are inconsistent. Parallel to increasing trends in pre-pregnancy obesity, we hypothesised similar increasing GWG trends.
Objectives: The study examined trends in GWG in South Carolina (SC), using methods to reduce bias. We also examined whether the 12-year trends in GWG varied according to race/ethnicity and pre-pregnancy weight.
Methods: Data came from SC birth certificates, 2004 to 2015. We calculated standardised GWG z-scores (GWGZ), using smoothed reference values to account for gestational age and pre-pregnancy body mass index. Quantile regression was used to examine trends in GWGZ, adjusting for pre-pregnancy weight status, race/ethnicity, parity, WIC participation, smoking during pregnancy, residence, age, and birth cohort.
Results: Among 615 093 women, the mean GWGZ was -0.4 (SD = 1.3), which increased from -0.4 in 2004-2005 to -0.2 in 2014-2015. GWGZ increased at the 5th, 10th, 25th, 50th, and 75th percentiles (ranging 0.04 to 0.73 units), with differential trends observed in sub-groups by pre-pregnancy weight and racial/ethnic group. Notably, non-Hispanic White women showed larger increasing trends (0.89 units) compared to non-Hispanic Black (0.55 units) and Hispanic (0.76 units) women in the 5th percentile. Decreasing trends were seen overall for the 90th (-0.02) and 95th percentile (-0.06 units) but positive trends were not seen among women experiencing obese class 1 (no change in 90th and 95th), and 2 (0.01 units in 90th, -0.02 units in 95th).
Conclusions: This study shows increasing GWGZ trends from the 5th to the 75th percentiles and decreasing trends in 90th and 95th percentiles in SC for the last decade. Racial/ethnic and pre-pregnancy weight disparities did not improve over the study period. Future research is needed to confirm these findings in other states and to develop strategies to narrow racial and pre-pregnancy weight disparities at the highest and lowest percentiles.
Keywords: gestational weight gain; health inequalities; maternal obesity; pregnancy; quantile regression.
© 2020 John Wiley & Sons Ltd.