Spacing babies

An association between interpregnancy intervals of less than 18 months and an increased incidence of poor perinatal outcomes, including low birth weight, preterm birth, and small for gestational age infants, has been shown by strong and consistent findings over many years and in a wide range of countries. The same three poor outcomes have also been consistently associated with interpregnancy intervals of greater than five years. The strength and consistency of research findings, together with the proposal of several plausible mechanisms by which both short and long intervals could result in these poor outcomes, has led to the widely held acceptance that these associations are causal. As interpregnancy interval is a modifiable feature of pregnancy, public health organisations, including the World Health Organization, have recommended intervals of no less than two years between giving birth and another pregnancy.1

The linked article by Ball and colleagues (doi:10.1136/bmj.g4333) seriously challenges this evidence.2 By analysing several interpregnancy intervals for the same mother, rather than comparing intervals between different mothers, they …