Interpregnancy Interval After Termination of Pregnancy and the Risks of Adverse Outcomes in Subsequent Birth

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We thank the authors for their report1 but are concerned that the analysis was too simplified to truly understand the association of interpregnancy interval and subsequent preterm birth.
When evaluating the demographic categories, gestational age was grouped as 12 weeks or less compared with more than 12 weeks. This type of categorization fails to allow an analysis reflecting when abortions are performed and to use this analysis, if correct, to properly counsel patients. Approximately 53% of all abortions in the United States are performed at 7 weeks of gestation or less.2 Grouping together women who undergo abortion at 10 weeks with those who undergo abortion at 6 weeks is potentially inappropriate statistically. For this analysis to have the ability to guide clinical practice, gestational age categories cannot simply be conveniently packaged into bivariate groups. The authors need to present analyses with clinically applicable gestational age ranges such as 7 weeks or less, 8–10 weeks, and 11–14 weeks (all first trimester) as well as 15–20 and 21–24 weeks or more in the second trimester. Because the primary outcome was preterm birth, gestational age at the time of abortion (as well as type of abortion, especially in the second trimester) is potentially the most important confounder and needs the utmost attention during analysis. If the authors do not have sufficient numbers in each group to perform such analyses, this very significant limitation needs to be recognized before the information is used clinically for patient counseling, especially given the overly weak adjusted association.

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