Reference intervals for hemoglobin and hematocrit in a low-risk pregnancy cohort: implications of racial differences

Objective: As anemia in pregnancy is associated with adverse perinatal outcomes, we sought to define the mean and the fifth percentile of Hb and Ht using a contemporary multiethnic large cohort of low-risk pregnancies, and assess potential racial differences. Methods: We conducted a retrospective cohort study on women who delivered between 1 January 2008 and 31 December 2013 in Reggio Emilia County, Italy. Linear mixed effects models were used to describe changes in mean Hb and Ht, while quantile regression with matrix-design bootstrap defined changes in the fifth percentile of Hb and Ht, controlling for race, maternal age, smoking, and pregnancy number. Results: We analyzed 23,657 hemograms from 7318 pregnancies and 6870 women. Multivariate analysis showed that when compared to Caucasians', African women's mean Hb and Ht were respectively 0.24 (95%CI 0.3-0.17) g/dl and 0.7 (95%CI 0.8-0.5) % lower, while Asian mothers' were 0.11 (95%CI 0.19-0.03) g/dl and 0.3 (95%CI 0.5-0.1) % inferior. Similarly, both African and Asian women had lower fifth Ht percentiles (-1, 95%CI -1.3 to -0.6, and -0.4, 95%CI -0.7 to -0.04) than Caucasians, while African mothers also had lower fifth Hb percentile (0.3, 95%CI 0.5-0.1). The fifth percentile for Hb and Ht were, respectively, 11.3 (95%CI 11-11.5) g/dl and 32.8 (95%CI 32.3-33.4) % in the first trimester, 10.4 (95%CI 10.1-10.6) g/dl and 30.2 (95%CI 29.6-30.8) % in the second trimester, 10.1 (95%CI 9.8-10.3) g/dl and 30.6 (95%CI 30-31.1) % in the third trimester. Conclusions: We provided contemporary references to define anemia in pregnancy, and we confirmed that even in pregnancy, African and Asian women have lower Hb and Ht than Caucasian. Racial and population-specific references may have significant clinical and public health implication for more accurate disease diagnosis and appropriate treatment.