NON-SYNCYTIAL SOURCES OF FETAL DNA IN TRANSCERVICALLY RECOVERED CELL-POPULATIONS

We have previously shown that fetal DNA can be detected in swabs and f lushings obtained from the lower uterine pole prior to the termination of pregnancy. The presence of syncytiotrophoblast vesicles in transce rvically retrieved samples suggested that this distinctive placental t issue was an abundant source of fetal DNA and a valuable resource in p renatal diagnosis strategies, In a more extensive study involving 150 terminations of pregnancy between 7 and 17 weeks gestational age, 29% of transcervically retrieved samples contained visible syncytial vesic les. Flushing of the uterine pole more frequently contained syncytia t han direct aspiration (39% compared with 26% of samples) but this diff erence was not statistically significant, No samples >14 weeks gestati onal age contained syncytia. Polymerase chain reaction analysis using Y-sequence specific-nested primers indicated the presence of fetal DNA in the absence of intact syncytial vesicles. We therefore examined sa mples by in-situ hybridization using Y-specific DNA probes, Positive l abelling was observed in syncytial vesicles where present and in clump s of unidentified fetal cells. In addition, high numbers of naked nucl ei were labelled in samples devoid of syncytia, These isolated nuclei are possibly derived from disrupted syncytia, and may be an important and hitherto overlooked contributory factor in fetal material which co llects at the lower uterine pole.