Short interpregnancy intervals and adverse perinatal outcomes in high-resource settings: An updated systematic review

Background: This systematic review summarises association between short interpregnancy intervals and adverse perinatal health outcomes in high-resource settings to inform recommendations for healthy birth spacing for the United States. Methods: Five databases and a previous systematic review were searched for relevant articles published between 1966 and 1 May 2017. We included studies meeting the following criteria: (a) reporting of perinatal health outcomes after a short interpregnancy interval since last livebirth; (b) conducted within a high-resource setting; and (c) estimates were adjusted for maternal age and at least one socio-economic factor. Results: Nine good-quality and 18 fair-quality studies were identified. Interpregnancy intervals <6 months were associated with a clinically and statistically significant increased risk of adverse outcomes in studies of preterm birth (eg, aOR ≥ 1.20 in 10 of 14 studies); spontaneous preterm birth (eg, aOR ≥ 1.20 in one of two studies); small-for-gestational age (eg, aOR ≥ 1.20 in 5 of 11 studies); and infant mortality (eg, aOR ≥ 1.20 in four of four studies), while four studies of perinatal death showed no association. Interpregnancy intervals of 6-11 and 12-17 months generally had smaller point estimates and confidence intervals that included the null. Most studies were population-based and few included adjustment for detailed measures of key confounders. Conclusions: In high-resource settings, there is some evidence showing interpregnancy intervals <6 months since last livebirth are associated with increased risks for preterm birth, small-for-gestational age and infant death; however, results were inconsistent. Additional research controlling for confounding would further inform recommendations for healthy birth spacing for the United States.