Large Population-Based Health Care Databases for Maternal and Infant Outcomes: the Role of Maternal Age, Race, and Interpregnancy Interval

Abstract

Delayed childbearing is associated with increased risks of adverse outcomes. The precise form with which risks increase with maternal age remain unclear. Different distributions of age-related risk factors across racial groups may result in different relationships between maternal age and pregnancy risks by maternal race, though race-specific relationships between maternal age and pregnancy outcomes have not been elucidated. Short interpregnancy (delivery to conception) intervals, common among older mothers, are associated with adverse outcomes, possibly due to an association between short interpregnancy interval and unplanned pregnancy. Short intervals among older mothers are often planned and thus may not be associated with increased risk. The impact of maternal age on the relationship between interpregnancy interval and pregnancy outcomes is not known. Using large, population-based databases drawn from Canada and the United States, we estimated absolute risks of maternal and infant outcomes according to maternal age at first birth among nulliparous women to produce risk curves. We stratified analyses by maternal race to estimate risk curves according to racial group. We estimated absolute risks of maternal and infant outcomes according to interpregnancy interval, stratified by maternal age categories. Risks of hypertensive disorders of pregnancy, major congenital anomalies, and severe maternal morbidity increased gradually until age 30 or 35, then accelerated. Cesarean delivery, gestational diabetes, and indicated preterm delivery risks increased progressively with age. Fetal and infant mortality risk curves were j-shaped, with nadirs near age 30. Within racial groups, risks at older ages were most pronounced for black and American Indian/Alaska Native women. Short interpregnancy intervals were associated with increased risks for women of all ages. Severe maternal morbidity risks were increased at 6-month compared with 18-month intervals for women ≥35 (risk ratio: 2.7 [95% CI 2.3-3.2]), but not for women 20-34 (1.1 [1.0-1.2]). Increased spontaneous preterm delivery risk at 6-month intervals was greater for women 20-34 (RR 1.7 [1.6-1.7] than women ≥35 (1.4 [1.3-1.5]. Increased risks of adverse fetal-infant outcomes and indicated preterm delivery at short intervals did not vary by maternal age. These findings may inform clinical counseling and family planning decisions regarding delayed childbearing and pregnancy spacing for older mothers.