Effect of Maternal Age on the Risk of Stillbirth: A Population-Based Cohort Study on 37 Million Births in the United States

The objective of our study was to evaluate the incidence and effect of maternal age on the risk of stillbirth. We conducted a population-based cohort study using the Centers for Disease Control and Prevention's "Linked Birth-Infant Death" and "Fetal Death" data files. We excluded all births of gestational age under 24 weeks and those with reported congenital malformations. We estimated the adjusted effect of maternal age on the risk of stillbirth using logistic regression analysis. There were 37,504,230 births that met study criteria, of which 130,353 (3.5/1,000) were stillbirths. Rates of stillbirth remained constant throughout the 10 years. As compared with women between the ages of 25 and 30, decreasing maternal age was associated with the following risk of stillbirth: odds ratio (OR) 0.95 (95% confidence interval [CI] 0.93 to 0.97) for ages 20 to 25; OR 0.97 (95% CI 0.94 to 0.99) for ages 15 to 20; and OR 1.32 (95% CI 1.18 to 1.47) for ages <15. Increasing maternal age was associated with an increasing risk of stillbirth: OR 1.02 (95% CI 0.99 to 1.04) for ages 30 to 35, OR 1.25 (95% CI 1.21 to 1.28) for ages 35 to 40, OR 1.60 (95% CI 1.53 to 1.67) for ages 40 to 45, and OR 2.22 (95% CI 1.91 to 2.53) for ages >45. Although the overall risk is low, the risk of stillbirth increases considerably in women at the extremes of the reproductive age spectrum. Antenatal surveillance may be justified in these women.