Objective: To investigate the effect of parity and interpregnancy interval (IPI) on perinatal outcomes in advanced maternal age (AMA) parturients. Methods: A population-based retrospective cohort study of all women older than 40 years, who had a singleton live birth after 24 weeks in the United States in 2017 Women were categorized to three groups by parity and interval from last delivery: primiparas, multiparas with IPI ≤ 5 years, and multiparas with IPI > 5 years. Primary outcome was composite adverse neonatal outcome (preterm delivery <34 weeks, birthweight <2000 g, neonatal seizure, neonatal intensive care unit admission, Apgar score <7 at 5 min, or assisted ventilation >6 h). Secondary outcome was composite adverse maternal outcome and other adverse perinatal outcomes. Univariate and multivariate analysis were used to compare between groups. Results: During 2017, 3,864,754 deliveries were recorded into the database. Following exclusion, 109,564 AMA gravidas entered analysis. Of them, 24,769 (22.6%) were nulliparas, 39,933 (36.4%) were multiparas with IPI ≤ 5 years, and 44,862 (40.9%) were multiparas with IPI > 5 years. Composite neonatal outcome was higher in nulliparas and in multiparas with IPI > 5 years, in comparison to multiparas with IPI ≤ 5 years (16% vs. 13% vs. 10%, respectively, p < 0.05). Maternal composite outcome was similar between groups. In the multivariable analysis, relative to nulliparas, only multiparity with IPI ≤ 5 years had a protective effect against the composite neonatal outcome (aOR 0.97, 95% CI 0.95–0.99, p < 0.001). Conclusion: Among AMA gravidas, multiparity with IPI ≤ 5 years has a significant protective effect against adverse neonatal outcomes when compared to nulliparas. Multiparity with IPI > 5 years is no longer protective.
