When birth spacing does and does not matter for child survival: an international comparison using the DHS

A large body of research has found an association between short birth intervals and the risk of infant mortality in developing countries, but recent work from highly developed countries has called these claims into question, arguing that previous estimates have been biased by a failure to adequately control for unobserved heterogeneity. This study addresses this issue by estimating within-family models on a sample of 4.5 million births from 77 countries at various levels of development. We show that even after controlling for unobserved maternal heterogeneity, intervals less than 24 months substantially increase the probability of infant death, and this relationship is present in all countries in our analysis. We do show, however, that the importance of birth intervals as a determinant of infant mortality varies inversely with maternal education. Finally, we demonstrate that the mortality-reducing effects of longer birth intervals are strong at low levels of development but decline steadily towards zero as populations become healthier and wealthier. These findings offer a clear way to reconcile previous research showing that birth intervals are important for infant mortality in low-income countries, but much less consequential in high-income settings.