Group B Streptococcus (GBS) in Pregnancy: Screening, Treatment and What to Expect

Group B streptococcus (GBS) is a common bacterium that many pregnant people carry without knowing it. A simple swab test late in pregnancy tells your care team whether you carry it, and if you do, antibiotics given through an IV during labor lower the chance your baby develops a GBS infection. GBS is not an STI, and carrying it does not mean you did anything wrong.

Seek emergency care right away if your newborn shows any of these signs, even after a normal delivery and even if you tested negative: fever, trouble breathing, extreme sleepiness or limpness, trouble feeding, or a bluish tint to the skin. These can appear on the day of birth or show up weeks later, and they need immediate medical attention.

What Is Group B Strep?

GBS is a type of bacteria that normally lives in the gut and can also be found in the vagina and rectum. It is not related to strep throat, and it is not sexually transmitted. Carrying GBS causes no symptoms in most adults. The concern in pregnancy is that GBS can pass to a baby during labor and delivery, and in rare cases it can cause a serious newborn infection such as sepsis, pneumonia, or meningitis.

When and How Screening Happens

The American College of Obstetricians and Gynecologists (ACOG) recommends universal GBS screening for pregnant people between 36 weeks and 37 weeks, 6 days of pregnancy. Your provider or midwife will collect a swab from the vagina and rectum; some people are able to do this swab themselves with guidance. The sample is cultured in a lab, and results are usually available before you go into labor.

Two situations mean you may not need this routine culture, because you’re already treated as GBS-positive for delivery:

You had a urine infection caused by GBS at any point during this pregnancy.
A previous baby of yours had invasive GBS disease.

What a Positive Result Means

A positive GBS culture means the bacteria were found in your sample at the time of testing. It does not mean you are sick, and it is not a reflection of your hygiene or health choices. About 1 in 4 pregnant people test positive. A positive result simply tells your care team to plan for IV antibiotics once labor starts.

How Intrapartum Antibiotics Work

“Intrapartum” means during labor. If you test positive, you’ll typically receive antibiotics through an IV after labor begins and continuing until delivery. Penicillin is the first-choice antibiotic for most people. If you have a penicillin allergy, ACOG recommends allergy testing during pregnancy when possible, since testing can help clarify whether penicillin or a closely related antibiotic is still a safe option for you. Depending on the allergy and local resistance patterns, alternatives such as cefazolin, clindamycin, or vancomycin may be used instead.

A key detail: these antibiotics only work if given during labor. Taking antibiotics for GBS earlier in pregnancy does not prevent colonization, because the bacteria can return quickly. This is why the timing of the test — close to when labor is likely to start — matters.

If Your GBS Status Is Unknown When Labor Starts

Sometimes labor begins before results are back, or before the test was done. In that case, your care team may recommend antibiotics anyway if any of these are present:

Labor starting before 37 weeks of pregnancy
Your water has been broken for 18 hours or more
A fever of 100.4°F (38.0°C) or higher during labor

A Simple Decision Path

Around 36 weeks, your provider collects a vaginal-rectal swab for GBS culture.
If the result is negative, no GBS antibiotics are planned for labor (unless a risk factor above comes up).
If the result is positive, IV antibiotics are planned once labor starts or your water breaks.
If you have a penicillin allergy, ask about allergy testing or which alternative antibiotic fits your situation.
If you’re scheduled for a cesarean birth before labor starts and before your water breaks, GBS antibiotics generally aren’t needed — confirm this with your provider, since it depends on your specific plan.

Getting Ready for Your GBS Test: A Checklist

Ask your provider when your swab is scheduled, since timing near 36–37 weeks matters.
Mention any penicillin or other antibiotic allergies well before your due date, not just at the appointment.
Tell your provider if you had a UTI at any point this pregnancy or if a previous baby had GBS disease.
Ask how and when you’ll get your result, and what the plan is if it’s positive.
If you’re planning a home birth or birth center delivery, ask how GBS-positive results are managed in that setting.

Extra-Caution Situations

Some situations call for closer attention from your care team:

Preterm labor: Babies born before 37 weeks are at higher risk for GBS disease, so antibiotics are often recommended even without a completed culture.
Penicillin allergy: This changes which antibiotic is used and may call for allergy testing during pregnancy.
Prior baby with GBS disease: This history alone leads to antibiotics in labor, regardless of this pregnancy’s culture result.
GBS found in urine this pregnancy: This is treated as a positive result for delivery planning, even if a later swab culture were negative.

What Happens After Birth

Most babies born to a GBS-positive parent who received antibiotics in labor are born healthy and need no special treatment. Hospitals typically watch newborns for signs of infection in the hours after birth, and how closely depends on factors like whether antibiotics were given in time and whether the baby was born early. Ask your baby’s care team what monitoring is planned in your specific case.

Evidence Limits

This page covers general screening and treatment recommendations from ACOG and the CDC. It does not cover every possible antibiotic option, every allergy scenario, or how individual hospitals implement monitoring for newborns. Research on a GBS vaccine is ongoing, but no vaccine is available yet. Your own plan should come from your provider, since it depends on your test results, allergies, and how your labor unfolds.

Frequently Asked Questions

Does testing positive for GBS mean I did something wrong?

No. GBS is a common bacterium, and about 1 in 4 pregnant people carry it at any given time. It is not caused by hygiene, diet, or sexual activity, and it is not an STI.

Can GBS make me sick during pregnancy?

Most people who carry GBS have no symptoms at all. In some cases, GBS can cause a urinary tract infection during pregnancy, which is treated when it’s found and is also treated as a positive result for labor planning.

If I’m having a scheduled cesarean, do I still need GBS antibiotics?

Generally, if a cesarean happens before labor starts and before your water breaks, GBS antibiotics aren’t needed. Confirm this with your care team, since your specific plan and any change in circumstances (like labor starting early) can affect this.

Can I take antibiotics before labor to clear GBS ahead of time?

No. Antibiotics taken before labor don’t prevent GBS from returning, because the bacteria can recolonize quickly. This is why treatment is timed to labor itself rather than given earlier in pregnancy.

Educational Disclaimer

This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. It does not cover every clinical scenario, antibiotic option, or hospital protocol, which can vary by provider and location. It does not create a provider-patient relationship. Always talk with a licensed healthcare provider about your specific pregnancy, test results, allergies, and birth plan before making any medical decisions. If you are having a medical emergency, call 911 or go to the nearest emergency room.