Blood-sampling collection prior to surgery may have a significant influence upon biomarker concentrations measured
among all patients was not significantly increased over the median pre-TOP fDNA concentration, but our data show an increase in fDNA after TOP only after 8 weeks of gestation. This increase occurred in 11 of 17 patients when pregnancy was later than 9.5 weeks of gestation (Fig. 1). The increase in fDNA at later gestations could be attributable to either an increase in placental size/mass or disruption of the fetomaternal circulation. Using Doppler studies, Jauniaux et al. (7 ) showed that placental blood flow is not established until 8–9 weeks of gestation. Thus, we would not necessarily expect to find FMH after TOP earlier than this gestational age. In support of this, Leong et al. (8 ) found no fetal cells in the blood samples of women after surgical TOP at 6 weeks menstrual age. We therefore suggest that the source of this DNA may be fetal hematopoietic cells within newly established placental blood vessels that are disrupted as a result of the TOP procedure and that the increased fDNA concentrations may indicate excessive FMH after 9 weeks of gestation. Plasma fDNA concentrations in many patients, however, unexpectedly decreased after the TOP procedure. Because no intravenous fluid bolus was given to any patient before the procedure, a dilution effect is unlikely. This decrease might be explained instead by the physiologic differences in how fDNA enters the maternal circulation. It is generally believed that in pregnant women the source of cell-free fetal nucleic acids is placentally derived apoptotic cells (9 ). Some fDNA sequences are detectable in membrane-bound apoptotic vesicles (10 ). This particleassociated form is believed to protect fetal nucleic acids from degradation by nucleases in maternal blood (11 ). After elective TOP, fDNA is liberated directly into the maternal circulation from the sudden disruption of the fetomaternal interface; thus it may not be protected in apoptotic bodies. We therefore suggest that unprotected posttermination fDNA sequences are vulnerable to destruction by maternal nucleases, leading to the rapid decrease in these sequences after elective termination in some patients. Future study should define the association between post-TOP cell-free fDNA concentrations, measured by real-time PCR, and cellular trafficking, determined by the traditional Kleihauer–Betke test, in a large cohort of patients at various gestational ages. In addition, the correlation between the alteration in fDNA concentrations and triggering of the maternal immune response remains to be elucidated. Current measurement of fDNA is based on Y-chromosome-specific sequence detection, which is not applicable to women who carry a female fetus. Therefore, the continued development of fetal genderindependent markers, such as fetal/placental specific mRNA, in the maternal circulation is essential (12 ). Comparison of fetal globin gene expression with placentally derived gene expression may allow us to definitively determine whether the increased fetal nucleic acids seen after 9 weeks of gestation in maternal plasma are from a placental or hematopoietic source (13 ). Dr. Wataganara’s maternal-fetal medicine fellowship is supported in part by Anandamahidol Foundation, Thailand. We thank Olivera Vragovic for help in organizing the study and enrolling the patients, and Dr. Dittakarn Boriboonhirunsarn for insightful comments on the manuscript.