Infant mortality and causes of death by birth weight for gestational age in non-malformed singleton infants: a 2002-2012 population-based study.

OBJECTIVE: To explore the associations between birth weight for gestational age (GA) and infant mortality as well as causes of infant death.

STUDY DESIGN: A population-based observational study conducted between 2002 and 2012 included 203,620 non-malformed singleton live births from Slovenia. Poisson regression analyses were performed to estimate the crude relative risk (RR) and adjusted RR (aRR) for infant mortality by birth weight percentiles stratified by the GA subgroups term, moderate-to-late preterm, very preterm and extremely preterm.

RESULTS: Compared with appropriate for GA (AGA) term infants (referent-AGA), infant mortality was significantly higher in small for GA (SGA) term infants [aRR=2.79 (1.41-5.50)], with significant cause-specific infant mortality risk for neuromuscular disorders [RR=10.48 (2.62-41.91)]. The differences in infant mortality and cause-specific infant mortality in preterm subgroups between referent-AGA and SGA were insignificant.

CONCLUSIONS: In the Slovenian population, birth weight for GA is significantly associated with infant mortality only in infants born at term.