Objective To examine the associations between extremes of maternal age (≤ 17 years or ≥ 40 years) and delivery outcomes.

Design Retrospective cohort study.

Setting Urban maternity hospital in Ireland.

Population A total of 36,916 nulliparous women with singleton pregnancies who delivered between 2000 and 2011.

Methods The study population was subdivided into five maternal age groups based on age at first booking visit: ≤ 17 years, 18–19 years, 20–34 years, 35–39 years and women aged ≥ 40 years. Logistic regression analyses were performed to examine the associations between extremes of maternal age and delivery outcomes, adjusting for potential confounding factors.

Main Outcome Measures Preterm birth, low birth weight, admission to the neonatal unit, congenital anomaly, caesarean section.

Results Compared to maternal age 20–34 years, age ≤ 17 years was a risk factor for preterm birth (adjOR 1.83, 95% CI 1.33–2.52). Babies born to mothers ≥ 40 years were more likely to require admission to the neonatal unit (adjOR 1.35, 95% CI 1.06–1.72) and to have a congenital anomaly (adjOR 1.71, 95% CI 1.07–2.76). The overall caesarean section rate in nulliparous women was 23.9% with marked differences at the extremes of maternal age; 10.7% at age ≤ 17 years, adjOR 0.46 (95% CI 0.34–0.62) and 54.4% at age ≥ 40 years, adjOR 3.24 (95% CI 2.67–3.94).

Conclusions Extremes of maternal age need to be recognised as risk factors for adverse delivery outcomes. Low caesarean section rates in younger women suggest that a reduction in overall caesarean section rates may be possible.