Objective: We tested the hypothesis that short interpregnancy intervals (IPIs) increase the risk for preterm birth (PTB), recurrence of PTB, and delivery at early extremes of gestational age.
Study design: Using the Missouri Department of Health's birth certificate database, we performed a population-based cohort study of 156,330 women who had 2 births from 1989-1997. The association between IPI and subsequent pregnancy outcome was assessed.
Results: The shortest IPIs (<6 months) increased the risk of extreme PTB (adjusted odds ratio, 1.41; 95% CI, 1.13-1.76). IPIs of <6 months and 6-12 months increased the overall risk of PTB (adjusted odds ratios, 1.48 [95% CI, 1.37-1.61] and 1.14 [95% CI, 1.06-1.23], respectively) and PTB recurrence (adjusted odds ratios, 1.44 [95% CI, 1.19-1.75] and 1.24 [95% CI, 1.02-1.50], respectively).
Conclusion: The risk of PTB and its recurrence increases with short IPIs, even after adjustment for coexisting risk factors. This highlights the importance of counseling women with either an initial term or preterm birth to wait at least 12 months between delivery and subsequent conception.