Maternal age and body mass index as risk factors for rectovaginal colonization with group B streptococci

Objective To examine the effect of including maternal age and body mass index (BMI; calculated as weight in kilograms divided by the square of height in meters) as additional risk factors in the traditional risk-based strategy at term pregnancies consisting of previous early-onset group B streptococcus (GBS) disease, GBS bacteriuria during pregnancy, maternal temperature of 38.0 degrees C or more intrapartum, and rupture of membranes of 18 h or longer. Methods A secondary analysis of a Danish cohort including 902 pregnant women. Exposures were maternal age and pre-pregnancy BMI. Outcome was rectovaginal GBS colonization at the time of labor. The logistic regression analysis adjusted for parity, gestational age, vaginal delivery, and smoking. Results The GBS prevalence was 17% in the entire population, 35% among participants older than 40 years, and 23% among those with a BMI of 25 or greater. Including maternal "age > 40" as an additional risk factor increased the sensitivity of the risk-based strategy from 21% to 26% and decreased the specificity from 90% to 87%. Inclusion of "BMI >= 25" increased the sensitivity from 21% to 57% and decreased the specificity from 90% to 59%. Conclusions Maternal age and BMI might be included as additional risk factors in risk-based programs for identification of GBS-positive laboring women to receive intrapartum antibiotics prophylaxis.