Missing Twins: Fetal Origins, Institutions, and Twin-singleton Mortality Convergence

An important number of twins are missing because of their substantially greater mortality risk in early ages relative to singletons. This paper has a twofold goal. First, it investigates whether, as children age, the twin-singleton inequality in mortality rates vanishes, and if yes, when. Second, it analyzes how the timing of mortality convergence is affected by the quality of political institutions. We use a sample of more than 3 million births from numerous countries in sub-Saharan Africa. Twins represent 3.2% of the sample, and children are followed up to the age of 25. We find that mortality is substantially higher for twins, but the difference persists only to around the age of 5. Importantly, the timing of mortality convergence is shortened by better quality political institutions. The findings yield two major conclusions. First, biology-induced disadvantages can be partially remedied through appropriate policy interventions. Second, the fetal origins hypothesis, which holds that the risk of adult morbidity and mortality is positively affected by intrauterine growth retardation, is not universally valid. In particular, better institutions are likely to offset the short-and long-term consequences of poor intrauterine conditions, attenuating the “missing twins” problem.