<p><b>Objective:</b> 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.</p> <p><b>Methods:</b> 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.</p> <p><b>Results:</b> 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.</p> <p><b>Conclusions:</b> 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.</p
