Influence of interpregnancy interval on neonatal morbidity.

Objective: We sought to assess the influence of birth spacing on neonatal morbidity, stratified by gestational age at birth.
Study Design: This was a population-based retrospective cohort study using Ohio birth records, 2006 through 2011. We compared various interpregnancy interval (IPI) lengths in multiparous mothers with the rate and risk of adverse newborn outcomes. The frequency of neonatal intensive care unit admission or neonatal transport to a tertiary care facility was calculated for births occurring after IPI lengths: <6, 6 to <12, 12 to <24, 24 to <60, and ≥60 months, and stratified by week of gestational age. Neonatal morbidity risk was calculated for each IPI compared to 12 to <24 months (referent), and adjusted for the concomitant influences gestational age at birth, maternal race, age, and prior preterm birth.
Results: We analyzed 395,146 birth outcomes of singleton nonanomalous neonates born to multiparous mothers. The frequency and adjusted odds of neonatal morbidity were lowest following IPI of 12 to <24 months (4.1%) compared to short IPIs of <6 months (5.7%; adjusted odds ratio [adjOR], 1.40; 95% confidence interval [CI], 1.32-1.49) and 6 to <12 months (4.7%; adjOR, 1.19; 95% CI, 1.13-1.25), and long IPIs 24 to <60 months (4.6%; adjOR, 1.12; 95% CI, 1.08-1.17) and ≥60 months (5.8%; adjOR, 1.34; 95% CI, 1.28-1.40), despite adjustment for important confounding factors including gestational age at birth. The lowest frequency of adverse neonatal outcomes occurred at 40-41 weeks for all IPI groups. The frequency of other individual immediate newborn morbidities were also increased following short and long IPIs compared to birth following a 12- to <24-month IPI.
Conclusion: IPI length is a significant contributor to neonatal morbidity, independent of gestational age at birth. Counseling women to plan an optimal amount of time between pregnancies is important for newborn health.
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