Impact of Formaldehyde on the in Vitro Proportion of Fetal DNA in Maternal Plasma and Serum

Abstract

Analysis of cell-free fetal DNA circulating in maternal blood is now well recognized as a useful tool for noninvasive prenatal diagnosis. Determination of fetal sex has modified prenatal diagnosis for women at risk of transmitting X-linked disorders (1), as well as management of pregnancies at risk for congenital adrenal hyperplasia (2). Routine determination of fetal rhesus D status has been evaluated by several groups (3)(4)(5). Despite the increasing number of potential applications, the low proportion of fetal DNA in a high background of maternal DNA dramatically limits its study, although some groups have already reported such analyses (6)(7)(8). Recently, Dhallan et al. (9) reported that the addition of formaldehyde to maternal blood increased the percentage of fetal DNA recovered. Because of its potential implications, this requires confirmation. We conducted a study similar to that of Dhallan et al. (9) but used an automated procedure for the extraction of nucleic acids and real-time quantitative PCR to provide more precise measurements of DNA. We recruited 30 pregnant women carrying a male fetus for this study. The mean (range) gestational age was 29 (15–39) weeks. After receipt of informed consent, blood was collected in 5-mL Vacutainer® Tubes with or without (EDTA tube) clot activator, with or without a neutral solution of formaldehyde (1 mL/L final concentration). Less than 24 h after blood sampling, each EDTA blood was centrifuged at 1600 g for 10 min at room temperature, and the plasma was carefully transferred to a new tube, avoiding disruption of the buffy coat. The plasma was again centrifuged in a similar manner and stored at −80 °C until further processing. For tubes containing clot activator, serum was obtained after a single centrifugation at 3000 g …