Women's Healthcare Topics

Will I be Tested for Group B Strep at 35 - 37 Weeks of Pregnancy?

Reviewed by James Brann, M.D.

Group B Strep or GBS

Between your 35 and 37th weeks of pregnancy you will be tested for Group B strep or GBS. Group B Strep is a type of bacteria that one to three women carry in their vagina. These bacteria, though benign to women in general, may pose serious and potentially life threatening consequences for your baby during birth. However,with proper screening women who test positive will be treated with an antibiotic during labor to prevent passing these bacteria on to their baby.

Most women who test positive for Group B Strep or GBS will deliver a normal and healthy baby. Without adequate diagnosis and treatment however, babies exposed to Group B Strep during the birthing process may face potentially life threatening side effects.

The Science Behind Group B Strep

Learn about testing for Group B Streptococal in pregnancy.

Group B Strep or GBS is a bacteria commonly found in the bowel, vagina and bladder. Usually it causes no symptoms at all, and people that carry these bacteria generally do so on a temporary basis.

Most women if tested consistently would probably come up positive as a carrier of Group B Strep at one point or another during their life. The only time Group B Strep is typically problematic is during pregnancy.

In rare cases Group B Strep may cause bladder or womb infections in a pregnant mother. It can infect the fetus before or during the birth process, though infection is rare.

Babies infected with Group B Strep may go on to develop pneumonia or even meningitis. Others may have long term problems such as hearing or vision loss during their lifetime.

In some infants Group B Strep doesn't develop until a week or more after delivery. This is an even more rare occurrence however than infection and detection immediately following delivery.

Group B Strep Antibiotic Protection for Baby

Current thinking for the treatment of Group B Strep is to give antibiotics during labor instead of when you have a positive culture in the office. This new thinking is because the antibiotics given for a positive culture in the office do not adequately protect the baby weeks later when you go into labor.

Also, a higher concentration of antibiotics can be achieved by given them through your intravenous port when in labor instead of taking them by mouth. The higher concentration of antibiotics allows for a higher amount to reach the baby and enter the amniotic fluid (fluid in the sac holding the baby), therefore protecting the baby better.

Antibiotic Protection is given in the Following Settings

  • When you have a positive screening culture in the office for GBS. The cultures are taken between the 35th to 37th week of pregnancy from both the vagina and rectal areas.

  • If you had a previous pregnancy with a history of a baby with early onset GBS.

  • If your urine tested positive for GBS bacteria during your current pregnancy.

  • If you were not tested for GBS during this pregnancy.

  • If you have a fever during labor.

  • If you are in labor before 37 weeks (preterm labor).

  • Antibiotics are given if your bag of water has been broken for longer than 18 hours.

Antibiotic used to Treat GBS

The most common antibiotic used for GBS is Penicillin G. The antibiotic is given every four hours until you deliver your baby. If you are allergic to Penicillin closely related antibiotic can be used called Cefazolin or Clindamycin.