Objective: To assess the frequencies of nucleated red blood cells (RBCs) in maternal blood during different stages of gestation and postpartum. Methods: Peripheral venous blood samples were collected longitudinally from 38 pregnant women from the first trimester to 3 months postpartum. Nucleated RBCs were isolated by using a triple-density gradient with Histopaque (Sigma Diagnostics, St. Louis, MO) and identified by Kleihauser-Betke acid stain.Results: The number of nucleated RBCs steadily increased from 3.9 (standard error 0.6) per 107 nucleated cells in early gestation (6-10 weeks) to 112.0 (standard error 7.5) per 107 nucleated cells near term and decreased rapidly after delivery. The number of nucleated RBCs was not related to the gender of the fetus or the ABO blood type compatibility between the mother and fetus. Conclusion: The number of nucleated RBCs in the maternal blood increase progressively throughout pregnancy, with some variation from subject to subject. Copyright (C) 1999 The American College of Obstetricians and Gynecologists.
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