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

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. 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. 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. 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.