Short interpregnancy interval and adverse birth outcomes in women of advanced age: a population-based study.

Purpose: Short interpregnancy interval (IPI) has been linked with adverse birth outcomes. However, the association in advanced age women needs further investigation. This study aims to examine the association between short IPI and adverse birth outcomes including preterm birth, post-term birth, low birth weight, and macrosomia, in a population of advanced age U.S. women.

Methods: The 2016 U.S. public-use natality data was analyzed. Analysis was restricted to women with second-order singleton live births who were ≥35 years at first live birth (n = 46,684). Multinomial logistic regression analysis was used to examine the association between short IPI and adverse birth outcomes.

Results: Short IPI in advanced age women was significantly associated with higher odds of extremely preterm birth (0-5 months IPI: adjusted odds ratio [AOR] = 2.43, 95% confidence interval [CI] = 1.07-5.52; 6-11 months IPI: AOR = 2.17, 95% CI = 1.09-4.31), very preterm birth (0-5 months IPI: AOR = 1.63, 95% CI = 1.04-2.56), and extremely low birth weight (0-5 months IPI: AOR = 2.43, 95% CI = 1.28-4.60) in the second delivery. An inverse relationship between short IPI and post-term birth was observed and no significant association between short IPI and macrosomia was found.

Conclusions: Short IPI in advanced age women increases the odds of adverse birth outcomes in the second delivery.