A bacterium that can be found in the vagina that can be picked up by the baby as he or she passes through during childbirth, causing a very serious infection in the newborn. Testing for GBS is usually scheduled between weeks 35 and 37. The practitioner will use vaginal and rectal swabs, and if the result is positive, the treatment is to administer either IV antibiotics during labor or oral antibiotics during the last weeks of pregnancy.