High prepregnancy BMI increases the risk of postpartum anemia

To assess the independent effect of prepregnancy BMI on the risk of postpartum anemia.

Pregnant women from North Carolina who enrolled in the Iron Supplementation Study at their first prenatal visit at <20 weeks gestation and who delivered a live infant were followed to the postpartum visit (n = 439). BMI had a curvilinear relation in the logit of postpartum anemia; therefore, a restricted quadratic spline with three knots at the inflection points was used to specify BMI. Multiple log binomial regression was used to quantify the relation between prepregnancy BMI and postpartum anemia after adjusting for maternal ethnicity/race, education, smoking, initial hemoglobin concentration, and prenatal iron supplementation.

Prevalence of postpartum anemia was 19.1%. After adjusting for confounders, we found that risk of postpartum anemia was similar for women with BMI values from 17 to 24 compared with women with a BMI of 20. Adjusted relative risk increased as BMI increased from 24 to 38. Women with a BMI of 28 had approximately 1.8 times the postpartum anemia risk of a woman with a BMI of 20 (95% confidence interval 1.3, 2.5), and obese women with a BMI of 36 had approximately 2.8 times the risk (95% confidence interval 1.7, 4.7).

These data suggest that high prepregnancy BMI substantially increases the risk of postpartum anemia. Postpartum anemia screening and iron supplementation of overweight and obese women may be warranted.