Subchorionic fibrin cultures for bacteriologic study of the placenta

Previous bacteriologic studies of the placenta have been hampered by a high rate of contamination of vaginal flora. In the present study, cultures of the subchorionic fibrin layer of the placenta were compared to conventional swab-cultures of the surface of the fetal membranes for recovery of aerobic and anaerobic bacteria. Parallel cultures of membrane surface and subchorionic fibrin (SCF) were done in the placentas of 33 deliveries suspected clinically of being complicated by infection (CD). Placentas from 46 uncomplicated deliveries were similarly cultured to serve as controls. SCF cultures were positive in 11 of 33 CD placentas and in only 1 of 46 controls (P less than 0.001). SCF cultures showed contaminating vaginal flora in 2 of 79 while surface cultures showed vaginal contamination in 16 of 79 (P less than 0.01). Recovery of pathogens was similar by the two methods: 10 of 33 and 14 of 33 respectively. One hundred ninety-one additional CD placentas were cultured by the SCF technique. Forty-nine of the 224 SCF cultures yielded pathogens with a predominance of group B hemolytic streptococci, anaerobic gram positive cocci and anaerobic gram negative rods (81 total isolates). Escherichia coli was isolated in 5 cases. Cultures showing exclusively contaminating vaginal flora were obtained from only 3 of the 224 placentas. Subchorionic fibrin cultures combine technical simplicity, low rate of contamination and excellent recovery of pathogens. The bacterial types found by this method are the predominant species that cause endometritis, pelvic infections, and neonatal septicemia. Subchorionic fibrin culture is a useful technique for the bacteriologic diagnosis of infection in the placenta.