Birth spacing and childhood mortality.

Recent evidence from developing countries indicates that there is a relationship between the length of the interval between consecutive births and the survival of the younger sibling. This relationship has long been observed in the developed world. A study conducted by the World Health Organization in 9 largely metropolitan locations in developing countries found a reverse J-shaped pattern, with mortality rates initially falling with increased intervals but showing an upturn for the longest intervals of 5-6 and 6 or more years. The birth interval-mortality link tended to be stronger for postneonatal rather than neonatal and child mortality. A World Fertility Survey (WFS) cross-national analysis found a longer birth interval substantially improved the survival chance of the youngest child in all 29 countries studied. This advantage persisted to 5 years of age. The ratio of the infant mortality rate of children born within an interval of less than 2 years to that of those born after an interval of 4 years ranged from 1.26 in Venezuela to 3.91 in Syria. A 2nd WFS study found that the birth interval-mortality link persisted when maternal education was controlled. More detailed analysis of data gathered for this study from Pakistan revealed that the association between birth interval and mortality of the younger sibling was unaffected by the early death of the older sibling. Although it has been hypothesized that competition between children for food and attention is the major causal mechanism in the birth interval-mortality link, this finding suggests that maternal depletion (giving rise to low birth weights and inadequate breast milk) plays a role. However, the additional finding that survivorship of order 5 and more births was unaffected by average spacing patterns once the length of the immediately preceding birth interval was controlled suggests that maternal depletion may not be cumulative. The data from Pakistan further show interval length to have the same effect on mortality of the older sibling, even when length of breastfeeding was controlled, suggesting that involuntary weaning because of the next pregnancy is the critical explanatory factor. This research points to the need for a renewed emphasis on contraception for spacing purposes.