BACKGROUND: The objective of this study was to determine if there are differences in common red blood cell (RBC) indices and platelet concentrations during pregnancy and to establish if any observed differences in these parameters were based on the patient's ethnicity. METHODS: From an electronic perinatal database which stores laboratory and clinical information on a large number of births at a regional hospital specializing in obstetrical care, RBC index and platelet concentration data were retrospectively analyzed at various time points throughout pregnancy. RBC index data was collected from 8,277 pregnant women (5,802 Caucasian pregnant women and 2,475 non-Caucasian pregnant women). Platelet concentration data was available from 8252 pregnant women (5,784 Caucasian pregnant women and 2,468 non-Caucasian pregnant women). RESULTS: Hemoglobin (HGB) levels were significantly higher amongst Caucasian women compared to non-Caucasian women (P at least <0.01) starting at 27 weeks gestation and proceeding until term. There was no significant difference in the mean PLT counts between Caucasian and non-Caucasian pregnant women at any point during gestation. CONCLUSION: There are ethnic differences in HGB levels, but not the platelet concentrations, during pregnancy. Based on this finding it would be reasonable to conduct formal prospective studies to determine the clinical significance of this difference and to establish the threshold for diagnosing gestational anemia, especially in pregnant non-Caucasian women.