Advanced maternal age and risk of antepartum and intrapartum stillbirth

Abstract

We sought to assess the risk of antepartum and intrapartum stillbirth subtypes among women of advanced age. This is a retrospective cohort study using the Missouri maternally linked data containing births from 1978 to 1997. We examined the impact of maternal age on total, antepartum and intrapartum stillbirth across five maternal age group quintiles (20-24, 25-29, 30-34, 35-39 and >or=40) using mothers aged 20-24 years as the referent category. By means of the Cox proportional hazards regression models we obtained adjusted hazards ratios that quantified the magnitude of association between maternal age and the stillbirth subtypes. The rates of antepartum and intrapartum stillbirth were greatest for older mothers (9.3/1000 and 1.2/1000 respectively) and lowest for gravidas aged 25-29 years (3.6/1000 and 0.8/1000 respectively). After adjusting for potentially confounding characteristics, older mothers still remained at greatest risk for antepartum and intrapartum stillbirth (adjusted hazards ratio = 3.6, 95% confidence interval = 2.9-4.4; and adjusted hazards ratio = 2.7, 95% confidence interval = 2.0-3.6 for antepartum and intrapartum stillbirth respectively). The risks for the two subtypes of stillbirth also increased with ascending maternal age in a dose-dependent pattern. As the demographic distribution of pregnant women persistently shifts to the right, care-providers will be increasingly confronted with elevated risks for adverse fetal outcomes among older mothers. Our results confirm this phenomenon and add new findings in relation to the elevated risk for intrapartum stillbirth among mothers advanced for age.