The contribution of preterm birth and intrauterine growth restriction to infant mortality in Tanzania.

Background: Our objectives were to examine the associations of neonatal and infant mortality with preterm birth and intrauterine growth restriction (IUGR), and to estimate the partial population attributable risk per cent (pPAR%) of neonatal and infant mortality due to preterm birth and IUGR.

Methods: Participants were HIV-negative pregnant women and their infants enrolled in Dar es Salaam, Tanzania. Gestational age calculated from date of last menstrual period was used to define preterm, and small for gestational age (SGA) was used as proxy for IUGR. Survival of infants was ascertained at monthly follow-up visits. Cox proportional hazard models were used to estimate the associations of preterm and SGA with neonatal and infant mortality.

Results: Study included 7225 singletons, of whom 15% were preterm and 21% were SGA; majority of preterm or SGA babies had birthweight ≥2500 g. Compared to term and appropriately sized babies (AGA), relative risks (RR) of neonatal mortality among preterm-AGA was 2.6 [95% CI 1.8, 3.9], RR among term-SGA was 2.3 [95% CI 1.6, 3.3], and the highest risk was among the preterm-SGA babies (RR 15.1 [95% CI 8.2, 27.7]). Risk associated with preterm was elevated throughout the infancy, and risk associated with SGA was elevated during the neonatal period only. The pPAR% of neonatal mortality for preterm was 22% [95% CI 17%, 26%] and for SGA it was 26% [95% CI 16%, 36%].

Conclusions: Preterm and SGA birth substantially increased the risk of mortality. Interventions for prevention and management of these conditions are likely to reduce of infant mortality in Tanzania.