Serial Analysis of Fetal DNA Concentrations in Maternal Plasma in Late Pregnancy

The discovery of fetal DNA in maternal plasma/serum has suggested new possibilities for noninvasive prenatal diagnosis (1) with applications in investigations of sex-linked diseases (2), rhesus D status (3), and β-thalassemia (4). Biologically, fetal DNA concentrations have been found to increase with gestational age, with a sharp increase toward the end of pregnancy (5). This latter phenomenon has been postulated to be related to the imminence of delivery (6). Consistent with the latter hypothesis, women with preterm labor have been found to have a higher concentration of fetal DNA in their plasma (7)(8). These results suggest that circulating fetal DNA concentrations are undergoing a time of flux during the late third trimester, but detailed information on the dynamics of maternal plasma fetal DNA is not available for this stage of gestation. In this study, we performed a serial analysis of fetal DNA concentrations in maternal plasma during the late third trimester. We recruited 33 healthy pregnant women from the Department of Obstetrics and Gynaecology, Prince of Wales Hospital, Hong Kong. All had ultrasonic evidence of male fetuses. Fetal sex was confirmed at delivery. Ethics approval was obtained from the Clinical Research Ethical Committee of the Chinese University of Hong Kong. Informed consent was obtained in all …