Group B strep in pregnancy
Group B Streptococcus (GBS) bacteria commonly live in the gut and genital tract and usually cause no symptoms. They matter in pregnancy because they can be passed to the baby during birth, and GBS disease can be very serious for newborns.
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The short answer
CDC says healthcare providers should screen all women for GBS during each pregnancy, in the 36th or 37th week. Women who test positive are not sick, but they get IV antibiotics during labor, which protects the baby. Antibiotics work only if given during labor — not before.
The test
CDC describes it as simple and painless: a sterile swab is rubbed on the vagina and rectum and sent to a laboratory. Testing happens late in pregnancy because GBS comes and goes naturally, so an earlier result may not reflect what is present at delivery. Screening should happen even if a cesarean birth is planned.
Antibiotics during labor
Antibiotics are given through a vein during labor; penicillin and ampicillin are the most common. Other antibiotics are used for people with a severe allergy. CDC notes that taking antibiotics by mouth, or before labor begins, does not prevent GBS disease in babies, because the bacteria can grow back quickly.
Why it matters, in CDC’s example
| Mother tested positive and… | Baby’s chance of GBS disease |
|---|---|
| received antibiotics during labor | About 1 in 4,000 |
| did not receive antibiotics during labor | About 1 in 200 |
From CDC’s “Preventing Group B Strep Disease in Newborns.” CDC also notes about 1 in 10 women have mild side effects from penicillin, and about 1 in 10,000 have a severe allergic reaction.
Common questions
- Does a positive GBS test mean I have an infection?
- No. CDC says women who test positive are not sick; they are at increased risk of passing the bacteria to the baby during birth.
- Is there a vaccine for group B strep?
- Not currently. CDC says vaccines are under development.
- Do I need GBS screening if I am having a planned cesarean?
- Yes. CDC says screening should happen even when a cesarean birth is planned.
Sources
- Screening for Group B Strep Bacteria (opens in a new tab) — Centers for Disease Control and Prevention (CDC)
- Preventing Group B Strep Disease in Newborns (opens in a new tab) — Centers for Disease Control and Prevention (CDC)
- About Group B Strep Disease (opens in a new tab) — Centers for Disease Control and Prevention (CDC)
Questions about this page
Tell us if something here is unclear or a source has changed. We cannot answer questions about your own pregnancy or care — please ask your OB, midwife, or care team. National Maternal Mental Health Hotline: call or text 1-833-TLC-MAMA (1-833-852-6262). Crisis: call or text 988.
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