Maternal age: an independent risk factor for cesarean delivery.

Objective: To evaluate whether there is an increased risk of cesarean delivery in women who delay childbearing into their later reproductive years, using a well-defined cohort and controlling for difference in baseline susceptibility such as complications of pregnancy and labor.

Methods: The current study included all women at least 20 years of age delivering their first child and evaluated between 1988-1991 as part of the prospective Yale Health in Pregnancy Study (N = 735). All women planned to deliver at Yale-New Haven Hospital. The study group was divided into three maternal age groups: 20-29 (N = 422), 30-34 (N = 239), and 35 and over (N = 74). Information collected included demographic characteristics, medical history, pregnancy complications, labor complications, mode of delivery, and pregnancy outcome.

Results: The cesarean delivery rates for the three age groups were 16.8% (71 of 422), 26.8% (64 of 239), and 32.4% (24 of 74), respectively. This trend was highly significant when evaluated with chi 2 for linear trend (P = .0002). Within groups of women with and without complications of pregnancy or labor, cesarean rates increased with maternal age. Using stepwise logistic regression to adjust simultaneously for confounding variables, adjusted odds ratios were 1.6 (95% confidence interval [CI] 0.9-2.7) for the women aged 30-34 and 2.3 (95% CI 1.1-4.8) for the 35 and older age group.

Conclusions: Maternal age appears to be an independent risk factor for cesarean delivery. The reasons for this clinically important and statistically significant increased risk are unclear, but may be due to physician and patient concern over pregnancy outcome in older women.