Group B Streptococcus colonization and higher maternal IL-1β concentrations are associated with early term births.

Association between maternal Group B Streptococcus (GBS) colonization diagnosed between 35 and 37 weeks of gestation and early term birth (between 37 and 39 weeks) and maternal-fetal inflammatory response associated with this condition were tested. In this cohort study of women delivering at term at Centennial Women's Hospital in Nashville, TN, GBS status and other clinical and demographic data were obtained from medical records. Exposed women were those testing positive for GBS (GBS positive [n = 490]) and the unexposed tested negative for GBS (GBS negative [n = 1,127]). To determine the inflammatory response associated with GBS, a cross sectional study, maternal and fetal plasma biomarkers (IL-1β, IL-2, IL-6, IL-8, and TNF-α) were measured in the same cohort. T-tests and logistic regression determined association between GBS status, biomarker concentrations and early term birth. Gestational age was reduced to 271.1 (95% CI 270.4, 271.1) for cases compared to 274.7 (95% CI 274.4, 275.1) days for controls (p < 0.0001). The odds of early term birth was increased by threefold in cases (OR 3.28; 95% CI 2.60-4.15; p < 0.0001). The mean birth weight in cases (3285.3 g) (95% CI 3242.6, 3327.9) was lower than the controls, 3373.8 g (95% CI 3348.9, 3398.7) (p = 0.0004). Maternal IL-1β was greater in cases (22.8 ng/ml; range 5.2-157.7 ng/ml) compared to controls (5.7; range 2.4-69.5 ng/ml; p < 0.0001). IL-1β was higher in fetal plasma in cases vs. controls (20.33 vs. 8.18 ng/ml; p = 0.01). A 10 ng/ml increase in maternal IL-1β was associated with increased risk for GBS infection (OR: 1.628, CI: 1.163-2.278; p = 0.0045). GBS colonization shortened gestational age at term and IL-1β concentration in maternal plasma is an indicator of GBS status.