Quantification of all fetal nucleated cells in maternal blood between the 18th and 22nd weeks of pregnancy using molecular cytogenetic techniques

Different types of nucleated fetal cells (trophoblasts, erythroblasts, lymp hocytes, and granulocytes) have been recovered in maternal peripheral blood . In spite of many attempts to estimate the number of fetal cells in matern al circulation, there is still much controversy concerning this aspect. The numbers obtained vary widely, ranging from I nucleated cell per 10(4) to 1 per 10(9) nucleated maternal cells. The purpose of our project was to dete rmine the absolute number of all different types of male fetal nucleated ce lls per unit volume of peripheral maternal blood. Peripheral blood samples were obtained from 12 normal pregnant women known to carry a male fetus bet ween 18 and 22 weeks of pregnancy. Three milliliters (3 ml) of maternal blo od has been processed without any enrichment procedures. Fluorescence in si tu hybridization (FISH) and primed in situ labeling (PRINS) were performed, and fetal XY cells were identified (among maternal XX cells) and scored by fluorescent microscopy screening. The total number of male fetal nucleated cells per milliliter of maternal blood was consistent in each woman studie d and varied from 2 to 6, cells per milliliter within the group of normal p regnancies. The number of fetal cells in maternal blood, at a given period, is reproducible and can therefore be assessed by cytogenetic methods. This confirms the possibility of developing a non-invasive prenatal diagnosis t est for aneuploidies. Furthermore, we demonstrate that it is possible to re peatedly identify an extremely small number of fetal cells among millions o f maternal cells.