Association of ABO incompatibility with elevation of nucleated red blood cell counts in term neonates

OBJECTIVE: Nucleated red blood cells in the circulation in term neonates ha ve been associated with a wide range of pathologic conditions. We sought to examine the relationship between nucleated red blood cells in the circulat ion of term neonates and maternal-neonatal blood type compatibility. STUDY DESIGN: We prospectively collected umbilical blood from all live-born neonates delivered at our institution. Venous blood was analyzed for nucle ated red blood cells and is reported as the number of nucleated red blood c ells per 100 white blood cells. We reviewed maternal and neonatal records f or neonates born at greater than or equal to 37 weeks' gestation for correl ative clinical data. Statistical analysis was performed with the SAS statis tical software package (version 6.12; SAS Institute, Inc, Cary, NC). Kruska l-Wallis analysis was used as a nonparametric test. RESULTS: We evaluated 1661 neonates delivered during the study period and f ound a mean (+/- SD) of 9.29 +/- 18.56 nucleated red blood cells per 100 wh ite blood cells (range, 0-327 nucleated red blood cells per 100 white-blood cells). Nucleated red blood cell counts were lower in ABO-compatible mater nal-fetal dyads (mean:+/- SD, 8.29 +/- 12.84 nucleated red blood cells per 100 white blood cells; range, 0-216 nucleated red blood: cells per 100 whit e blood cells) than in ABO-incompatible dyads (mean +/- SD, 13.16 +/- 13.16 nucleated red blood cells per 100 white blood cells; range, 0-327 nucleate d red blood cells/100 white blood cells; P=.006). Neonates of mothers with blood groups A and B had significantly lower nucleated red blood cell count s (P<.05). Dyads with maternal type O and neonate type B had significantly higher nucleated red blood cell counts (P <.002). Nonparametric testing det ermined that type O mother and type B neonate combinations had significantl y higher umbilical cord nucleated red blood cell counts (P<.001). CONCLUSION: Maternal-fetal ABO incompatibility is associated with elevation of nucleated red blood cell count in term neonates. Nucleated red blood ce ll elevation does not always connote a serious pathologic process, however, because ABO incompatibility usually does not adversely affect neonatal out come. The clinical significance of an elevated nucleated red blood cell cou nt thus is limited.