Interpregnancy interval and maternal and neonatal morbidity: a nationwide cohort study

This study aimed to assess the association between interpregnancy interval (IPI)—the time from childbirth to conception of the next pregnancy—and maternal and neonatal morbidity. The World Health Organization (WHO) currently recommends an IPI of at least 24 months after a live birth to reduce adverse birth outcomes. However, assessing the relationship between IPI and perinatal outcome is complicated by confounding factors. We conducted a nationwide population-based cohort study using Swedish registry data, allowing for adjustment of maternal characteristics and health at first birth. The study population consisted of all women with a singleton, live, and vaginal first birth with a second singleton birth within five years during 1997–2017, covering 327,912 women and 655,824 neonates. IPI was grouped into six-month intervals with 24–29 months as the reference. The association between IPI and morbidity was examined using multivariate logistic regression. For women having a vaginal delivery at their first birth, intervals < 24–29 months were associated with decreased maternal morbidity and unaffected neonatal morbidity. Intervals > 24–29 months were associated with increased maternal and neonatal morbidity. Our findings question the relevance of WHO’s recommendation of an IPI of at least 24 months in a high-income country.