Stillbirth and subsequent risk of infant mortality

Background: Infant mortality is an important indicator of the health and wellness of a society. Despite high expenditures in healthcare delivery, the US still performs poorly on the infant mortality index as compared to other industrialized nations. Although multiple risk factors for infant mortality have been identified and investigated, the influence of prior pregnancy experience on subsequent infant mortality is under-researched. In this study, we examine the association between stillbirth in the first pregnancy and the risk for infant mortality in the second pregnancy in a large population sample. Methods: This is a retrospective cohort study that utilized information from the Missouri maternally linked cohort data files from 1989 through 2005. The exposure was stillbirth in the first pregnancy, and the primary outcome was infant mortality in the second pregnancy. We generated adjusted estimates from multi-variable logistic regression models, and used odds ratios to approximate relative risks. Results: Women who experienced stillbirth in their first pregnancy were more likely to be of advanced age, black, and obese with no children (p<0.01). They also had higher rates of pregnancy-related complications, such as insulin-dependent diabetes, chronic hypertension, pre-eclampsia, or eclampsia (p<0.01). A history of stillbirth was associated with subsequent infant mortality (AOR=2.25, 95% CI 1.73-3.84) and neonatal mortality (AOR=3.09, 95% CI 1.96-4.90) after adjustment for the afore-mentioned confounders. Conclusions: Women with a history of stillbirth experience higher risks for subsequent infant mortality. Women's previous childbearing experiences could serve as important criteria in determining appropriate interconception strategies to improve feto-infant health and survival.