When should screening for Group B Streptococcus (GBS) in pregnancy be conducted?

Screening for Group B Streptococcus (GBS) in pregnancy is ideally conducted at 35-37 weeks of gestation. This timing is critical because it allows for the identification of women who carry GBS, enabling appropriate interventions to reduce the risk of transmission to the newborn during delivery.

Conducting the screening at 35-37 weeks ensures that the results are relevant and that any potential maternal colonization is recent, as GBS colonization can fluctuate over the course of the pregnancy. Testing at this point also provides ample time to plan for prophylactic intrapartum antibiotic therapy for those who test positive, significantly decreasing the risk of early-onset GBS disease in the infant.

Screening too early, such as before 20 weeks or even at 28-30 weeks, may not accurately identify women who are currently colonized with GBS at the time of delivery due to changes in colonization status throughout the pregnancy. Additionally, conducting the screening during labor does not give enough time to implement preventive measures should a woman test positive for GBS at that time. Thus, the recommended timeframe of 35-37 weeks strikes the right balance for effective management and prevention of complications associated with GBS in newborns.