Which test is performed to screen for Group B Streptococcus during pregnancy?

The screening for Group B Streptococcus (GBS) during pregnancy is typically performed using a vaginal-rectal culture. This test is ideally conducted between 35 and 37 weeks of gestation and serves to identify carriers of the bacteria who may pose a risk of transmission to the newborn during delivery.

The reason this testing method is favored is that GBS colonization is most effectively identified through cultures taken from the lower genital tract. A vaginal-rectal culture can provide a comprehensive assessment of the presence of GBS, ensuring that appropriate intrapartum antibiotic prophylaxis can be administered if needed, thereby reducing the risk of early-onset GBS disease in newborns.

Other testing methods mentioned, such as urine tests, blood tests, or amniotic fluid analyses, are not standard protocols for GBS screening. Urine tests primarily evaluate for urinary tract infections, blood tests assess various other conditions, and amniotic fluid analysis is mainly used in particular situations like assessing labor or infection, not for direct screening of GBS. Therefore, the vaginal-rectal culture remains the most suitable and effective method for this specific purpose in the obstetrical setting.