The Transplacental Passage of Fetal Leukocytes into the Maternal Blood

The sex chromosome was used as a marker to detect leakage of fetal cells through the placenta into the maternal circulation during the course of, and after pregnancy. PHA–stimulated peripheral blood cultures from healthy pregnant and post–partum women were used for this study. Twelve of 14 women, with male cells in their peripheral blood, gave birth to male babies. The cultures of six women, who bore male infants, were examined pre and post partum. None of them revealed male cells prior to delivery but five of them had male cells after delivery. Male karyotypes could be detected in the maternal blood for as long as six months after delivery. Our results indicate that the fetal leukocytes can traverse the placenta and enter the maternal circulation more readily at two time periods. One occurs during the first trimester; and the other, immediately following delivery. The passage of these cells may be important in the immunologic phenomena of parity related to paternally derived transplantation antigens. Fetal sex determination will probably be reliable only if the mother has had no previous male pregnancies, and if two or more male cells per 200 metaphases are found.