Pregnancy

Group B Strep Test in Pregnancy: When It's Done and What a Positive Result Means

By the Find Her Doctor editorial team · Updated November 1, 2026 · 6 min read

The group B strep (GBS) test is a quick swab of the lower vagina and rectum done between 36 and 37 weeks of pregnancy. About 1 in 4 pregnant people carry GBS bacteria, usually without symptoms. If you test positive, you'll get IV antibiotics during labor, which greatly lowers the chance your baby develops a serious GBS infection after birth.

If your result just came back positive and you're feeling a little thrown, you're far from alone. "Positive" sounds alarming. In practice, it mostly changes one thing: when you head to the hospital once labor starts.

What is group B strep?

Group B Streptococcus is a type of bacteria that normally lives in the intestines and genital tract. It comes and goes over time, which is why testing happens close to your due date. It's harmless for most adults.

The concern is the baby. During a vaginal birth, a baby can be exposed to GBS. A small number of exposed babies develop early-onset GBS disease in the first week of life, which can cause sepsis, pneumonia or meningitis. GBS is a leading cause of serious infection in newborns, and antibiotics during labor are very effective at preventing it.

Myth vs. fact

Myth: GBS is an STI, or it means I'm not clean. Fact: No. It's not a sexually transmitted infection and isn't caused by hygiene. It's part of the normal bacteria many healthy adults carry. Yes, people ask this a lot, usually quietly.

Myth: I can clear it with probiotics or garlic before labor. Fact: There's no proven way to clear GBS before birth. Probiotics, garlic and similar remedies haven't been shown to prevent newborn GBS disease and shouldn't replace testing or IV antibiotics in labor.

Myth: I should take antibiotic pills now to get rid of it. Fact: Oral antibiotics before labor don't work, because the bacteria often come back by delivery. Only IV antibiotics during labor are proven to protect the baby.

Myth: I was negative last time, so I'll be negative this time. Fact: GBS comes and goes, so you need a new test in most pregnancies. More on that below.

Myth: Being GBS positive means no skin-to-skin or breastfeeding. Fact: No. It doesn't change skin-to-skin contact, rooming in or breastfeeding. Wash your hands before handling your baby, like everyone should.

When is the GBS test done?

ACOG recommends testing between 36 weeks 0 days and 37 weeks 6 days. A result at that point predicts your GBS status at delivery for about five weeks. If you're still pregnant five weeks after a negative test, your provider may repeat it.

You may not need the swab if:

• GBS was found in your urine at any point this pregnancy. You'll be treated in labor regardless.
• You had a previous baby with GBS disease. You'll be treated in labor regardless.

What the swab is like

Your provider uses a cotton swab to gently collect a sample from the lower vagina and then the rectum. It takes a few seconds. It isn't painful, though the rectal part catches some people off guard. Some practices let you collect the swab yourself in the bathroom with instructions. Results usually come back within a few days, often on your portal first.

Tell your provider if you're allergic to penicillin. If you are, the lab may run extra tests on your sample to pick the best backup antibiotic. If you're not sure whether your "allergy" is real (many people were told as kids), say that too.

You're GBS positive. What labor looks like

Very little changes before labor. The key step is IV antibiotics once labor starts or your water breaks.

• Penicillin is the usual first choice. Ampicillin is also used.
• If you're allergic to penicillin, options include cefazolin, clindamycin or vancomycin, depending on how severe your allergy is and the lab results.
• Timing matters. Antibiotics given at least four hours before birth give the best protection.

In practice, that four-hour window is why your provider may ask you to come in a bit earlier once labor starts, and right away if your water breaks. If you live in the outer boroughs, on Long Island or upstate, talk through the timing plan with your provider ahead of time, including traffic. You'll get an IV line and doses every few hours until birth. Many people say it barely registers once labor is underway.

After birth, the baby's care team watches for signs of infection. If you got antibiotics for long enough, most babies need only routine observation.

Planned C-section?

If you have a planned C-section before labor starts and before your water breaks, you don't need antibiotics for GBS. (You'll still get the standard antibiotic given before any C-section.) If labor starts or your water breaks before surgery, you'll be treated for GBS.

What if your status is unknown when labor starts?

If you go into labor before you've been tested or before results are back, you'll typically get antibiotics if:

• You're in labor before 37 weeks
• Your water has been broken for 18 hours or more
• You have a fever of 100.4°F (38°C) or higher during labor
• A rapid test in labor is positive, if your hospital offers one

GBS positive vs. negative: what changes

Does GBS cause problems for me?

Usually not. GBS can occasionally cause a urinary tract infection in pregnancy, or rarely an infection of the uterus or amniotic fluid. Your provider treats these if they happen.

Does treatment in labor protect the baby completely?

Antibiotics during labor prevent most early-onset GBS disease, but they don't prevent late-onset disease, which can appear from about a week to a few months after birth. Call your baby's doctor right away if your newborn has a fever, trouble feeding, unusual sleepiness, breathing problems or irritability.

Do I need a GBS test every pregnancy?

Yes, in most cases. A negative result in one pregnancy doesn't predict the next, and a positive result in a past pregnancy doesn't mean you'll be positive again. People who were positive before are more likely to be positive again, so your provider may discuss repeating the test or planning antibiotics in labor. The exception: if a previous baby had GBS disease, you'll get antibiotics in labor in every future pregnancy.

Getting GBS testing in New York

GBS screening is part of standard prenatal care and is covered by most insurance plans, including NY Medicaid. If you haven't started prenatal care, it's not too late. Search the directory for OB/GYNs and midwives near you, browse certified nurse midwives in the Bronx, or see the prenatal visit schedule.

When to call your provider

Call your provider, or go to labor and delivery, if:

• Your water breaks, especially if you're GBS positive
• You have regular contractions and you're GBS positive or your status is unknown
• You have a fever of 100.4°F (38°C) or higher
• You're over 37 weeks and haven't been tested
• You have burning or pain when you urinate

If you're GBS positive, make sure the result and any penicillin allergy are in your hospital records and on your birth plan. Take a screenshot of the result on your phone too, in case you deliver somewhere other than planned.

Frequently asked questions

Sources

• ACOG — Prevention of Group B Streptococcal Early-Onset Disease in Newborns (Committee Opinion 797)
• ACOG — Group B Strep and Pregnancy FAQ
• CDC — Group B Strep Disease: Prevention
• MedlinePlus — Group B Streptococcal Infections

This article is for general education and is not medical advice. It does not replace an evaluation by a licensed clinician who knows your history. If you think you have a medical emergency, call 911.