There is also data showing that antibiotics are helpful during preterm labor for women who carry bacteria called group B streptococcus (GBS). About one in five women will carry GBS, and babies who get infected during labor and delivery can become very sick. Antibiotics can treat GBS and reduce complications of a subsequent infection in the newborn, but carry risks for the mother ( Ohlssen & Shah, 2009 ). Most care providers test women for the bacteria about a month before their due date. The test involves taking swab samples from the lower vagina and rectum. Because it can take two or three days for test results to be returned, the general practice is to go ahead and begin treating a woman for GBS before confirmation of infection if a woman is in preterm labor. Most doctors think that this presumptive treatment is justified because as many as one in four women test positive for GBS. Ampicillin and penicillin are the antibiotics most commonly used for treatment.