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.