Trends in Short Interpregnancy Interval Births in the United States, 2016-2022.

Objective: To measure contemporary trends in the prevalence of short interpregnancy interval (IPI) births in the United States.

Methods: We conducted a repeated cross-sectional analysis using 2016-2022 natality data from the National Vital Statistics System. We included all singleton live births to individuals with at least one prior live birth. We examined trends over time in short IPIs less than 18 months, as well as for specific durations within this time frame (less than 6 months, 6-11 months, and 12-17 months), using linear probability models that estimated changes in the prevalence of each IPI duration over time. We then estimated the prevalence of each short IPI duration by maternal race and ethnicity, socioeconomic characteristics (age, education, insurance payer at delivery), and geography (U.S. census region, state of residence).

Results: The study sample included 14,770,411 singleton live births to individuals with at least one prior live birth in 2016-2022. Roughly a third (29.8%) of births had an overall IPI of less than 18 months (5.0% less than 6 months, 11.0% 6-11 months, and 13.8% 12-17 months). For IPIs less than 6 months, a slight statistical decline in prevalence was identified over the study period in unadjusted and adjusted models (adjusted annual percentage point change -0.02, 95% CI, -0.03 to -0.02). Slight statistical increases in the prevalence of IPIs of 6-11 and 12-17 months were identified in unadjusted models but were no longer significant and reversed direction in adjusted models, respectively. Long-standing inequities in the distribution of the shortest IPIs (less than 6 months) were stable compared with prior work across the indicators examined in this study.

Conclusion: Overall, it appears the prevalence of short IPIs has remained stable between 2016 and 2022.