Maternal hemoglobin concentration during pregnancy and risk of stillbirth

Context High and low maternal hemoglobin concentrations during pregnancy have been reported to increase risk of small-for-gestational-age (SGA) birth, which is a predictor of stillbirth. The relationship between hemoglobin concentration during pregnancy and risk of stillbirth is unclear. Objective To study the associations among hemoglobin concentration at first measurement during antenatal care, change in hemoglobin concentration during pregnancy, and risk of stillbirth. Design, Setting, and Participants Population-based, matched case-control study of births from 1987 through 1996 in Sweden including 702 primiparous women with stillbirths occurring at 28 weeks' gestation or later and 702 primiparous women with live births. Main Outcome Measures Risk of stillbirth, classified as malformed or nonmalformed, antepartum or intrapartum, preterm or term, and SGA or non-SGA, compared by maternal hemoglobin concentration at first antenatal measurement and weekly changes in hemoglobin concentration during pregnancy, adjusted for maternal age, body mass index, height, smoking, socioeconomic status, and week of first hemoglobin measurement. Results In multivariate analyses, compared with women with hemoglobin concentrations of 126 to 135 g/L at first antenatal measurement, women with concentrations of 146 g/L or higher were at increased risk of stillbirth (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.0-3.3). This risk was slightly increased when the analysis was restricted to antepartum stillbirths without malformations (OR, 2.0; 95% CI, 1.1-3.8). When we further restricted the analyses to preterm and SCA antepartum nonmalformed stillbirths, the ORs increased to 2.7 (95% Cf, 1.1-6.4) and 4.2 (95% CI, 1.3-13.9), respectively. Excluding women with preeclampsia and eclampsia further increased these risks. Average weekly change in hemoglobin concentration during early or tate pregnancy was not significantly associated with risk of stillbirth, although a larger decrease in concentration tended to be protective. Anemia (hemoglobin concentration <110 g/L) was not significantly associated with risk of stillbirth in multivariate analyses (OR, 1.2; 95% CI, 0.5-2.7). Conclusions High hemoglobin concentration at first measurement during antenatal care appears to be associated with increased risk of stillbirth, especially preterm and SGA antepartum stillbirths.