Placental cultures in the era of peripartum antibiotic use

Background: Histological examination of the placenta can provide valuable information that aids diagnosis and management for both the mother and the fetus. Positive placental cultures may also provide the clinician with valuable information on which to base therapy. Aims: To determine the incidence of positive placental cultures, the association with chorioamnionitis and whether the rate is affected by antibiotic administration in the peripartum period. Methods: A retrospective study of placentas submitted for histopathology and microbiology culture in higher risk deliveries over a 12-month period in a laboratory at a tertiary facility. Data collected included gestation age, duration of rupture of membranes, maternal fever, group B Streptococcus status, intrapartum antibiotics, placental culture result and the histopathology result. Results: Of the 412 placentas submitted, 26% (106 of 412) had histological evidence of in utero inflammation. Sixty-three percent (259 of 412) of placentas were submitted for culture. Of these, only 4.6% (12 of 259) had a positive culture result, with 75% (nine of 12) having histological evidence of acute inflammation. Group B streptococcus and Escherichia coli were the most common isolates. Forty-two per cent (five of 12) of these women had received peripartum antibiotics. Conclusions: Positive placental cultures are found in only a small number of placentas with histological evidence of chorioamnionitis and funisitis. The current method of placental swabbing and culture technique is highly specific but not sensitive. The value of performing current routine placental cultures appears limited.