Prenatal diagnosis on fetal cells from maternal blood: practical comparative evaluation of the first and second trimesters

Objectives - Several attempts have been made to determine the gestational p eriod in which the maximum number of fetal cells can be found in maternal b lood and consequently which is the best week in which to perform a reliable : non-invasive prenatal diagnosis. Most studies conclude that the number of nucleated red blood cells (NRBC) increases in line with gestation, but the number of cells that are fetal in origin (FNRBC) decreases in the third tr imester. The aim of the present study was to make a practical comparative e valuation of the first and second trimesters to ascertain the period in whi ch a greater number of FNRBC can be round of the total number of NRBC ident ified. Methods - Double density gradient and a posterior positive selection (CD71) by magnetic activated cell sorting (MACS) were employed. In the final frac tion, erythroblasts were identified using Kleihauer staining and were studi ed using the fluorescence in situ hybridization (FISH) interphasic techniqu e. Results - There was a significant difference (p < 0.05) between the mean nu mber of FNRBC found in the first and second trimesters. Conclusions The number of FNRBC increases from the first to the second trim ester. It appears that the optimum week in which to perform a reliable non- invasive prenatal diagnosis is around the 15th week. Copyright (C) 2001 Joh n Wiley & Sons, Ltd.