The effects of birth spacing on health and socioeconomic outcomes across the life course: evidence from the Utah Population Database

The relationship between the length of birth intervals and child outcomes has received increased attention in recent years, but few studies have examined offspring outcomes across the life course in North America. In this study we examine the relationship between birth intervals and a range of short- and long-term outcomes, including preterm birth, low birth weight, infant mortality, college graduation, occupational attainment, and adult mortality, using data from the Utah Population Database (UPDB). To study infant outcomes we use data on cohorts born 1947--2016, to study educational and occupational outcomes we use data on cohorts born 1950--1980, and to study adult mortality we use data on cohorts born 1900--1949, with mortality outcomes followed until 2016. We use linear regression, linear probability models, and survival analysis, and compare the results from models with and without sibling comparisons. Children born after a birth interval of 9-12 months have a higher probability of low birth weight, preterm birth, and infant mortality both with and without sibling comparisons; longer intervals are further protective, but to a much less dramatic extent, and the protective effect of longer intervals against low birth weight and preterm birth was clearer in cohorts born before the 1990s. Based upon sibling comparison analyses, even the very shortest birth intervals do not negatively influence educational or occupational outcomes, nor long-term mortality. These findings suggest that extremely short birth intervals can increase the probability of poor perinatal outcomes, but that any such disadvantages disappear over the extended life course