Inter-pregnancy interval and adverse outcomes: Evidence for an additional risk in health disparate populations

Short interpregnancy interval (IPI), <18 months between pregnancies, is a potential cause of adverse delivery and birth outcomes, and may be a particular issue among those with other risks. Our goal was to examine IPI and delivery/infant complications in Tennessee.

Birth certificate/vital records data included 101,912 women with a previous delivery. IPI groups (<6, 6-12, 12-18, 18-60 months) were compared on outcomes.

Thirty-nine percent of the deliveries had IPI <18 months, 9% were <6 months, rates 11% and 27% higher than nationally. Women with IPI <18 months were younger, lower educated with lower income, had higher BMIs, and were more likely to be unmarried, smokers, and have begun prenatal care later (p < .001). In adjusted analyses, IPI <18 months predicted elevated risk for precipitous labor, low-birth weight, preterm delivery, NICU admission, and infant mortality, with effects strongest for IPI <6 months. Finally, risks related to IPI <6 months were substantially higher for the lowest income women.

Rates of less than optimal IPI were high in this population already experiencing significant maternal-child health disparities, with short IPI a particular risk factor for poor outcomes for the most disadvantaged women, suggesting yet another precursor for adverse birth outcomes in those already most at risk.