Objective: To establish whether antibiotic prophylaxis against group B streptococcal infection may be a confounding factor in comparisons of rates of endometritis and urinary tract infection after vaginal delivery.
Design: Prospective study.
Setting: Maternity units at 48 hospitals in a regional surveillance network in France during 2001-2004.
Methods: The maternity units used a common protocol to establish whether antibiotic prophylaxis was indicated. Risk factors for endometritis and urinary tract infections were evaluated using multiple logistic regression.
Results: We analyzed 49,786 vaginal deliveries. The percentage of women receiving antibiotic prophylaxis varied widely and significantly among the maternity units (range, 4.4%-26.0%; median, 15.8%; 25th percentile, 12.1%; 75th percentile, 19.0%) (P < .001, by Mantel-Haenszel chi(2) test). The incidence rate of endometritis was significantly reduced from 0.25% to 0.11% by antibiotic prophylaxis (P = .001). There was a decrease in the incidence of urinary tract infection from 0.37% to 0.32%, but it was not statistically significant (P = .251).
Conclusions: A reduction in the incidence of endometritis was observed when intrapartum antibiotic prophylaxis against group B streptococcal infection was used. However, the proportion of women considered to be at risk of infection varied widely among institutions. Comparisons of rates of endometritis among maternity units, but not urinary tract infection rates, should take into account antibiotic prophylaxis as a significant confounding factor.