Fetal cells are present in the circulation of pregnant women and can be isolated using density gradient centrifugation and magnetic cell sorting. In the present study, maternal cell preparations were depleted for CD45- and CD14-positive cells and enriched for CD71-positive cells. The number of fetal nucleated cells was determined using fluorescence in situ hybridization for X and Y chromosomes. Analysis of maternal blood samples taken before and after transabdominal chorionic villus sampling (TA-CVS) showed an increase in the number of fetal cells in 10 out of 19 male pregnancies after the invasive procedure. This cellular transfusion was found to correlate with elevated maternal serum alpha-fetoprotein levels. TA-CVS-induced cellular transfusion may form a good in vivo system to optimize fetal cell isolation procedures and to study fetal cell dynamics and characteristics.