Rise in maternal serum α-fetoprotein concentration after chorionic villus sampling and the possibility of isoimmunization

Maternal serum α-fetoprotein concentrations were determined by radioimmunoassay in 72 patients immediately before and after chorionic villus sampling for prenatal diagnosis. Fifty percent showed a rise of ≥5 ng/ml. Assuming such rises represent fetal blood crossing the intervillous space, in 14% of the cases ≥60 μl of fetal blood was transferred at the time of chorionic villus sampling. A positive correlation was found between the magnitude of rise in maternal serum α-fetoprotein levels and the amount of villi removed (r = 0.39, p < 0.001). When cases were examined by number of passes, a greater rise in maternal serum α-fetoprotein levels was noted with multiple passes than with single passes for a given sample size. The transfer of ≥60 μl of fetal blood suggests that maternal sensitization to fetal antigens may occur after chorionic villus sampling. During biopsy, as small a sample of villi as necessary for diagnosis should be taken with as few catheter passes as possible.