Age-period-cohort analysis of low birth weight, early-term delivery, induction, and cesarean-section, US births 1990-2019.

Abstract

We conducted an age-period-cohort (APC) analysis to distinguish age, period, and cohort effects underlying temporal trends in low birth weight (LBW: <2500 g), early-term deliveries (ETD: 37-38 weeks), induction, and cesarean-section (c-section) using US birth records from 1994-2019 for all singleton, first, full-term (37-44 weeks gestation) births (n = 8 194 523). Using the APC-interaction method, we estimated age, period, and cohort effects as odds ratios with 95% CI. Age and period effects were observed for all outcomes. Pregnant women/people aged 40-44 years had increased odds of LBW (OR 1.23, 95% CI, 1.19-1.26), ETD (OR 1.24, 95% CI, 1.23-1.26), induction (OR 1.05, 95% CI, 1.04-1.06), and c-section (OR 2.28, 95% CI, 2.26-2.30) compared to the total population. Odds of LBW (OR 1.14, 95% CI, 1.13-1.16), ETD (OR 1.11, 95% CI, 1.10-1.12), and induction (OR 1.71, 95%,CI, 1.70-1.72) were higher in 2019 compared to the study period average. Cohort effects not explained by age and period effects were observed for women aged 40-44 years in 2019 indicated by higher odds of ETD (OR 1.08, 95% CI, 1.05-1.10), induction (1.10, 95% CI, 1.07-1.12), and c-section (OR 1.09, 95% CI, 1.06-1.11). These findings suggest obstetric management of pregnant women ≥40 years changed in recent decades in ways not expected based on age and temporal trends alone.