Changes in maternal hemoglobin during pregnancy and birth outcomes

The relationship between maternal hemoglobin (Hb) levels during pregnancy and birth outcomes has been controversial. Changes in Hb level during pregnancy may have an impact on birth outcomes. This study aimed to investigate whether changes in Hb levels from early to mid- or late pregnancy is associated with birth outcomes.

Participants were singleton mothers who delivered at the National Center for Child Health and Development between 34 and 41 weeks of gestation in 2010 and 2011 (n = 1,986). Hb levels were measured at three time points: early (<16 weeks), mid- (16-27 weeks), and late (28-36 weeks) pregnancy. Associations between changes in Hb levels from early to mid- or late pregnancy and birth outcomes (birth weight, Z-score of birth weight, placental weight, and placental ratio) were assessed by multiple regression, adjusting for maternal and fetal covariates.

A smaller reduction in Hb levels from early to mid- or late pregnancy was significantly associated with lower birth weight, Z-score of birth weight, placental weight, and placental ratio. Compared to women with an intermediate reduction from early to late pregnancy, women with the least reduction had a significantly increased risk of delivering low birth weight (LBW) (adjusted odds ratio [aOR], 2.0; 95% confidence interval [CI], 1.3-3.1) and small-for-gestational-age (SGA) (aOR, 1.6; 95% CI, 1.04-2.3) infants, while women with the greatest reduction had a significantly decreased risk of delivering SGA (aOR, 0.38; 95% CI, 0.23-0.65) infants, but an increased risk of high placental ratio (aOR, 1.7; 95% CI, 1.2-2.5).

Hb changes from early to mid- or late pregnancy were inversely associated with birth weight, placental weight, and placental ratio.