Prenatal sex determination by in situ hybridization on fetal nucleated cells in maternal whole venous blood.

Our aim was to evaluate whether the sex of a fetus could be determined in maternal whole venous blood by in situ hybridization without enrichment of fetal cells. This procedure is virtually without risks to the fetus or the mother. Blood samples were obtained from 59 women at different stages of pregnancy. Twenty preparations were discarded because they were technically unfit for in situ hybridization. Of the remaining 39 pregnant women, 18 had a male fetus, one had male twins, and 20 had a female fetus. Y-positive cells were detected in 12 of the 19 pregnancies with male fetuses and in two of the 20 pregnancies with a female fetus. The frequencies of cells with Y-signals ranged from 1 in 100,000 to 1 in 639. Our results show that fetal cells in maternal blood cannot be reliably used for prenatal diagnosis without prior enrichment of fetal cells.