At term, 10 to 30% of pregnant women have vaginal or rectal colonization with Group-B Streptococcus (GBS). Fetal infection at delivery is associated with significant neurologic morbidity and mortality. The Centers for Disease Control recommends GBS collection between 35 and 37 weeks gestation; if taken within 5 weeks of delivery, GBS status at delivery has a positive predictive value (PPV) of 87 to 100%. However, PPV falls to 43% if the culture is taken 6 weeks or more before delivery. We hypothesize approximately one third of patients at our institution delivering past their estimated due date have expired GBS cultures, defined as greater than 35 days old.METHODS:
A retrospective chart review from July 2015 to July 2016 included all women who delivered at or after 40 weeks gestation. Demographics, delivery information, GBS status, interval between culture and delivery, and neonatal data were collected. Patients were divided by week of gestational age at delivery, and rates of expired cultures compared by chi-square.RESULTS:
1,393 patients were included; they delivered between 40 and 42 weeks gestation at Mount Sinai West. 660 (47%) had expired cultures at delivery. Of those delivering during week 40, 328/971 (34%) had expired cultures; during week 41, 296/385 (77%) had expired cultures; this difference in expiration rates was significant (P<.0001). Expiration rate was also significantly greater in week 42 than in week 41. No neonatal GBS infections occurred.CONCLUSION:
Cultures should be repeated after 35 days, or initially collected at 37 weeks, to improve reliability.