Interpregnancy intervals and perinatal and child health in Sweden: a comparison within families and across social groups

Until recently a large body of research conducted in high-income countries had shown that children born after an especially short or especially long birth interval are at an elevated risk of preterm birth, low birth weight, being small for gestational age, as well as other poor perinatal outcomes. However, a handful of recent studies that have adjusted for shared family background more effectively have cast doubt on that conclusion. We use Swedish population data on cohorts born 1981-2010 and sibling fixed effects models to examine whether the length of the birth interval preceding the index person has an impact on the risk of preterm birth, low birth weight, and hospitalization during childhood. We additionally present for the first time for this particular research question analyses stratified by salient social characteristics such as maternal educational level, and maternal country of birth. Overall, we find few effects of birth intervals on our outcomes except for very short birth intervals. Short interpregnancy intervals (60 months) increase the probability of low birth weight and preterm birth. We also find that longer intervals (>42 months) decrease the probability of hospitalization during the first year of life, but interpregnancy intervals greater than 30 months increase the probability of hospitalization between ages 1-3. We find few differences in the patterns by maternal educational level, or by maternal country of origin after stratifying by the mother’s highest attained education. The results from this study contribute to the ongoing debate about whether the length of interpregnancy intervals matter for perinatal and child health in high-income countries.