Maternal Body Mass Index and the Risk of Fetal Death, Stillbirth, and Infant Death

Abstract

Worldwide, approximately 2.65 million stillbirths occurred in 2008, most of which were in low- and middle-income countries.¹ Stillbirths account for a large part of all perinatal deaths.¹ In addition, an estimated 3.6 million neonatal deaths occur each year.² Several studies have suggested that greater maternal body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) before or during early pregnancy is associated with an increased risk of fetal death,^3-6 stillbirth,^4,6,7 perinatal death,^5,6,8,9 neonatal death,^6-8,10 and infant death (Box).^6,10 However, not all studies found a significant association,^11-14 some possibly due to a low sample size or a low number of deaths.^11-14 The optimal prepregnancy BMI to prevent fetal and infant death has not been established. Some studies have reported J-shaped associations with a small increase in risk among women with low or moderate BMI (although not statistically significant),^6,7,12,14 while other studies reported a linear association.^3-5,8,9 Determining whether there are any threshold effects between maternal BMI and fetal and infant death could be important with regard to public health recommendations for women who plan pregnancies. To clarify the association between maternal BMI and risk of fetal death, stillbirth, and infant death, we conducted a systematic review and meta-analysis of the available evidence from published cohort studies. This study specifically determined the strength of the association, the shape of the dose-response relationship, potential confounding, and potential sources of heterogeneity in the results (including the definition of stillbirth and perinatal death).⁴