At which weeks of gestation should Group B Streptococcus (GBS) be checked?

Group B Streptococcus (GBS) screening is recommended to occur between 35 and 37 weeks of gestation. This timeframe is optimal for a few reasons. First, screening late in the third trimester ensures that the test results are relevant to the time of delivery, as GBS colonization can change throughout pregnancy.

Testing done too early, like at 28-30 weeks or even 32-34 weeks, can lead to inaccurate results because a mother might acquire GBS later in pregnancy. Additionally, performing the test too close to the delivery date (weeks 40-42) might not provide enough time to implement any interventions if the test result is positive since GBS prophylaxis, such as intravenous antibiotics during labor, is necessary to reduce the risk of transmission to the baby.

Thus, screening between 35 and 37 weeks allows for timely identification and management, thereby improving outcomes for both the mother and the newborn.