Fetal erythroblasts in maternal blood in relation to gestational age

Objective: To determine the distribution of fetal erythroblasts in the maternal circulation at different gestations. Materials and methods: Maternal blood was obtained from 152 normal singleton pregnancies at 11-40 weeks of gestation. Fetal erythroblasts were isolated using triple density gradient separation and anti-CD71 magnetic cell sorting techniques. The enriched erythroblasts were stained with Kleihauer-Giemsa and with fluorescent antibodies for the zeta (ζ), epsilon ( ) and gamma (γ) globin chains. The percentage of fetal cells positive for each stain was calculated. Fluorescence in situ hybridization for X and Y chromosomes was also performed. Comparison was made in the proportion of positive fetal erythroblasts among the different gestational ages. Results: The proportion of erythroblasts stained positive with γ-globin chain and Kleihauer-Giemsa decreased withgestation from a median of 2% at 11 weeks to 0.5% at 40 weeks. Similarly, there was a decrease in the percentage of Y-signal-positive cells from 1% at 11 weeks to 0.3% at 40 weeks. The proportion of enriched fetal erythroblasts stained positive with ζ- and -globin chains decreased exponentially from respective medians of 0.6% and 1.5% at 11 weeks to zero after 19 weeks and 24 weeks. Conclusion: In normal singleton pregnancy the percentage of fetal erythroblasts enriched from maternal blood decreases withgestation.