Multiple births mortality by maternal age at birth: a within-family analysis of Demographic and Health Survey data on 42 low-income countries

Background: Existing evidence suggests that children from multiple-births experience lower infant mortality with advanced maternal age, in contrast to what is observed for singletons. The role of unmeasured confounding, and whether this observation is also present in low-income countries where the infant mortality is higher than in Western countries, remain unknown. Methods: Using the Demographic Health Surveys data of over 6 million live births reported from 42 low-income countries, we applied mother fixed-effects in linear probability models with and without parity. Results: The infant mortality (as well as neonatal mortality) was highest among the twin offspring of younger mothers. Compared to infants of mothers age 24-25 at delivery, the infant mortality was highest (0.14 [0.13, 0.15]) among offspring of mothers younger than 18 years of age, and declined by around 0.01 until a mother reaches her late 30s. The overall pattern was robust to adjustment for parity to the model and estimation without mother fixed-effects. Similar patterns hold in Southern Asia and sub-Saharan Africa, and across different developmental settings. Conclusions: We observed a lower infant mortality among children from multiple births when the mothers were in the 30s compared to when mothers are in the mid-20s or younger also in low-income countries. Unlike previous findings, the lower mortality associated with advanced maternal age is visible from the mid-20s.