American Board of Family Medicine (ABFM) Practice Exam

What is the greatest risk factor for group B Streptococcus (GBS) infection in a pregnant woman?

1. Fetal tachycardia

2. Delivering at less than 35 weeks gestation

3. Rupture of membranes 12 hours before delivery

4. Gestational diabetes during pregnancy

The correct answer is: Rupture of membranes 12 hours before delivery

The greatest risk factor for group B Streptococcus (GBS) infection in a pregnant woman is characterized by the duration of rupture of membranes before delivery. Specifically, if the amniotic membranes rupture and remain unprotected for 12 hours or longer before the delivery occurs, this significantly increases the risk of GBS colonization of the infant. Prolonged rupture of membranes allows for an increased likelihood of bacterial migration from the vaginal flora, which can include GBS, leading to potential infection in both the mother and newborn. In contrast, while fetal tachycardia may indicate distress or complications, it is not specifically related to the increased risk of GBS. Delivering at less than 35 weeks gestation does carry its own risks, such as prematurity and associated complications; however, it is not the predominant risk factor for GBS infection itself. Gestational diabetes, while having its own set of implications for pregnancy, is also not directly linked to GBS risk. The primary concern with GBS arises from the timing of rupture of membranes, emphasizing the importance of monitoring this factor in labor management.