362: Interpregnancy interval and neonatal outcomes in a large US cohort

Abstract

Interpregnancy Interval (IPI) is the time between delivery and subsequent conception. An IPI of 18-24 months is considered ideal and an IPI<18 months has been associated with adverse neonatal outcomes including preterm birth and low birth weight, however data is largely from small cohort studies or non-US populations. We sought to evaluate the association between short IPI and adverse neonatal outcomes in a large, diverse data set. We conducted a retrospective cohort study using vital statistics birth certificate records between 2012-2015. Women with a singleton, non-anomalous pregnancy and at least one prior live birth were included for analysis. Women were stratified by the IPI as follows: <6 months, 6-11 months, 12 months-18 months, 18-23 months and >=24 months. Neonatal morbidity was the outcome of interest including preterm birth, low birth weight (<2500g), very low birth weight (<1500g), NICU admission, Apgar <7, and seizures. Maternal medical conditions and socioeconomic factors known to be associated with preterm birth were evaluated and controlled for in multivariable logistic regression. We identified 8,013,471 women with pregnancies meeting our inclusion criteria. Of those, 1,989,686 (31.3%) had an IPI of <18 months and 516.021 (6.44%) had a very short IPI of <6 months. Short IPI was associated with preterm birth, low birth weight and very low birth weight, 5 min Apgar less than 7, NICU admission and neonatal seizures. Maternal characteristics associated with short IPI included Black, Hispanic and Native American ethnicity, limited prenatal care, tobacco use in pregnancy, and Medicaid as payer source for delivery. Diabetes and hypertensive disorder, advanced maternal age and white and Asian race/ethnicity were not associated with short IPI. When controlling for multiple potential confounding variables, short IPI remained significantly associated with preterm birth, but no other adverse neonatal outcomes. The association appears inversely proportional to the IPI with an adjusted odds ratio of 1.05 (95%CI 1.04-1.06) and 1.42 (95%CI 1.41-1.44) for IPI <18 months and <6 months respectively. In this large, diverse data set, short IPI was significantly associated with preterm birth, but was not significantly associated with other adverse neonatal outcomes.