When does the CDC recommend screening for group B Streptococcus (GBS) in pregnant women?

The correct timing for screening for group B Streptococcus (GBS) in pregnant women is at 35-37 weeks of gestation. This recommendation is based on the understanding that GBS colonization can change during the course of pregnancy. Screening during this late gestational period allows for an accurate assessment of whether a woman is colonized with GBS right before labor, which is critical for managing the potential risks to the newborn.

If a woman tests positive for GBS at this time, she can receive appropriate intrapartum antibiotic prophylaxis to reduce the risk of early-onset GBS disease in the infant. This targeted approach helps ensure that the screening is timed to effectively inform the management plan around delivery, taking into account the dynamic nature of GBS colonization.

Screening at earlier points in pregnancy, such as during the first visit or at 16 weeks, may not provide an accurate risk assessment for the time of delivery. Similarly, screening at the onset of labor would not allow for timely interventions that could prevent the transmission of GBS to the newborn. Thus, the recommendation to screen at 35-37 weeks focuses on optimizing maternal and neonatal health outcomes.