First-trimester group B Streptococcus colonization of the cervix: a risk factor for maternal colonization at term?

Objective: To identify the prevalence of first-trimester cervical group B Streptococcus (GBS) colonization in routine obstetric patients and whether a relationship exists between first-trimester cervical GBS colonization and maternal GBS bacteriuria or GBS colonization at term.

Methods: An institutional review board-approved prospective, cohort study was performed. The study population included consecutively recruited, unselected obstetric patients who delivered at our medical center, presented for care in thefirst trimester and were followed for the duration of their pregnancies. Each patient consented to have an extra culture swab for GBS status obtained at the time of her first prenatal visit when a routine examination was performed. Urine and third-trimester culture data were also collectedfrom each study subject.

Results: Of the 90 women with complete delivery data, 17 (19%) hadfirst-trimester cervical cultures positive for GBS. Women with first-trimester cervical GBS colonization were more likely to have third-trimester colonization on screening cultures than were women whose initial cultures were negative (35% vs. 14%, p = 0.05). The sensitivity of a GBS-positive cervical culture for detecting the coexisting presence of GBS bacteriuria was 38%, with a positive predictive value (PPV) of 31% and negative predictive value of 89%. When the outcome of interest was expanded to include GBS bacteriuria or third trimester colonization, the PPV of a positive cervical culture increased to 73%.

Conclusions: First-trimester GBS colonization of the cervix may be as sensitive as antepartum GBS bacteriuria, an established risk factor, for predicting maternal GBS colonization at term.