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Infections Routine

Group B strep

Also known as Group B streptococcus, GBS, Streptococcus agalactiae. Screened at 36–37 weeks.

Group B strep (GBS) is a common bacterium that lives harmlessly in the digestive and genital tracts of about one in four pregnant people. Carrying it is not poor hygiene, not a sexually transmitted infection, and almost never makes the carrier sick. It matters for one reason: a baby can pick it up during birth, which occasionally causes a serious newborn infection. Prevention is simple and highly effective, a routine swab late in pregnancy and, if you carry it, antibiotics through a vein during labor.

Know the warning signs When to call a provider
How common
About 1 in 4 carry it
Roughly 10% to 30% of pregnant people, and it comes and goes.
When
Screened at 36–37 weeks
A vaginal and rectal swab late in pregnancy.
Urgency
Routine
Managed simply with antibiotics during labor if you test positive.
Outlook
Excellent with prophylaxis
Labor antibiotics have cut newborn GBS disease dramatically.

Understanding it

What is group B strep?

Group B strep is one of the many bacteria that live in and on us without causing trouble. It colonizes the gut and genital tract of roughly 10% to 30% of pregnant people, and for the carrier it is almost always silent and harmless. You do not catch it from food, water, or a partner, and a positive result says nothing about your hygiene or health.

Colonization is not permanent, either. GBS comes and goes, so you can test positive in one pregnancy and negative in another, or positive now and negative weeks later. That is why it is checked close to your due date, when the result best reflects what will be present at birth.

The attention is all about the newborn. A baby can be exposed while passing through the birth canal, and in a small share of cases this becomes early-onset GBS disease, a serious infection of the blood, lungs, or the lining around the brain in the first days of life. About half of colonized parents pass GBS to their baby.

Prevention works. A swab at 36 to 37 weeks tells your team whether you carry GBS, and if you do, antibiotics through a vein during labor protect your baby as they are born. Since this became routine, newborn GBS disease has fallen by roughly 85%.

Symptoms

What are the symptoms?

GBS causes no symptoms in the pregnant person and is found by screening, not by how you feel. The signs that matter appear in the newborn after birth.

Early signs

  • Usually no symptoms at all in the pregnant person
  • Occasionally a urinary tract infection caused by GBS, which is treated and also flags you for labor antibiotics

Emergency signs — call 911

  • In your newborn, call your baby's provider or seek emergency care right away for: fever or an unusually low temperature
  • Trouble feeding or refusing to feed
  • Trouble breathing, grunting, or fast breathing
  • Being limp, floppy, unusually sleepy, or hard to wake
  • Irritability, or a seizure

Why it matters

Risks to you and baby

Early-onset newborn disease

In the first week of life, GBS can cause sepsis (a bloodstream infection), pneumonia, or meningitis. It is serious, which is why we prevent it, but labor antibiotics have made it uncommon.

Late-onset newborn disease

GBS can also cause illness between one week and about three months of age. Labor antibiotics do not prevent this later form, so knowing your baby was exposed helps providers watch for it.

Rarely, an infection in you

GBS can cause a urinary tract infection during pregnancy and, uncommonly, a uterine infection around the time of birth. Both are treatable.

The overall picture is reassuring

With screening and labor antibiotics, the chance of your baby developing early-onset GBS disease is low. Most babies born to GBS-positive parents are perfectly healthy.

How it's found

How is it diagnosed?

GBS is found with a quick swab, not a blood test or a symptom check. Screening is late in pregnancy so the result reflects what will be present at birth.

Vaginal and rectal swab

A swab of the vagina and rectum at 36 to 37 weeks is cultured in the lab. The result is simply positive (you carry GBS) or negative.

Urine test

GBS found in the urine at any point in pregnancy means you will get antibiotics in labor regardless of the swab, because it reflects heavier colonization.

Rapid test in labor

If your GBS status is unknown when labor starts, a rapid test (NAAT) can sometimes be done, or antibiotics are given based on risk factors.

Routinely at 36 to 37 weeks in every pregnancy, because your status can change from one pregnancy to the next.

Treatment

How is it managed?

If you carry GBS, the whole plan is antibiotics through a vein during labor, getting protective levels to your baby as they are born. It works well.

Treatment paths

Antibiotics run intravenously once labor starts or your water breaks, continuing until birth. They are not given earlier because GBS grows back quickly, so treating ahead of time would not protect your baby at delivery.

Medication

Penicillin is the first choice, with ampicillin as an alternative. For a penicillin allergy, cefazolin, clindamycin, or vancomycin is used depending on how severe it is. Tell your provider about any penicillin allergy well before your due date so the right medication is ready.

Monitoring

Your newborn is observed for signs of infection, especially if antibiotics could not be given in time, for example with a very fast labor.

Can it recur?

Your status can differ each pregnancy, so you are screened again every time. If you had a previous baby with GBS disease, or GBS in your urine this pregnancy, you get antibiotics in labor automatically, without a positive swab.

What you can do

Can it be prevented?

  • Get screened at 36 to 37 weeks

    The swab is how your team knows whether you carry GBS. Keep this appointment in every pregnancy, since your status can change.

  • Report a penicillin allergy early

    Flagging a penicillin allergy ahead of time lets your provider choose the right alternative and, if needed, test which one your GBS will respond to.

  • Know the plan if your status is unknown

    If labor starts before you are screened, antibiotics are given based on risk factors like preterm labor, a long time since your water broke, or a fever, so your baby is still protected.

Who is more at risk

Risk factors

Carrying GBS
A positive screen is the main factor, and the reason antibiotics are given in labor.
Preterm birth
Delivery before 37 weeks raises a baby's risk of GBS disease.
Water broken for a long time
Membranes ruptured for 18 hours or more before birth increases the risk.
Fever in labor
A temperature of 100.4 F (38 C) or higher during labor is a risk factor and a reason for antibiotics.
GBS this pregnancy or a prior affected baby
GBS in your urine this pregnancy, or a previous newborn who had GBS disease, means antibiotics in labor regardless of the swab result.

Do not wait

When to call your provider or 911

  • After birth, call your baby's provider or seek emergency care immediately if your newborn has a fever or low temperature, trouble feeding, trouble breathing, or is limp, unusually sleepy, or hard to wake.
  • During pregnancy, tell your provider if you have a penicillin allergy, well before your due date.
  • Call when your water breaks or labor starts, so your antibiotics can be started on time if you are GBS positive or your status is unknown.
  • Let your team know if you had a previous baby with GBS disease or GBS in your urine this pregnancy, since that changes your labor plan.

Talking to your team

Questions to ask your provider

  • What was my GBS screening result?
  • If I am positive, when will antibiotics be started in labor?
  • I have a penicillin allergy: which antibiotic will you use, and do you need to test my sample?
  • What happens if my labor is too fast to give antibiotics in time?
  • What signs should I watch for in my baby after we go home?
  • Does being GBS positive change my birth plan at all?

Keep reading

More on group B strep

All pregnancy guides articles

Good to Know

Group B strep FAQs

Common questions about group B strep, answered.

Does testing positive for GBS mean I have an STD or did something wrong?

No. GBS is a normal bacterium that many healthy people carry. It is not sexually transmitted, not caused by anything you did, and it says nothing about your hygiene. It is simply common.

Will GBS make me sick?

Almost never. In the pregnant person it usually causes no symptoms; occasionally a urinary tract infection. It is screened for to protect your baby, not because it threatens you.

Why are the antibiotics given only during labor and not now?

Because GBS grows back quickly. Treating it earlier would not keep it away by the time your baby is born. Antibiotics through a vein during labor put protective levels in place at exactly the right moment.

What if my labor is too fast and I do not get the antibiotics in time?

It happens, and your team plans for it. Your newborn is watched more closely for signs of infection and treated promptly if needed. Even part of a dose helps.

Are the antibiotics really necessary?

For a GBS-positive parent, they sharply lower the chance of a serious newborn infection, which is why they are recommended. If you are allergic to penicillin, effective alternatives exist. Raise any concerns with your provider.

Will I have GBS in my next pregnancy?

Maybe. GBS comes and goes, so your status can differ next time, which is why you are screened again in every pregnancy rather than relying on a past result.

Can I still have a vaginal birth?

Yes. Being GBS positive is not a reason for a cesarean. You can plan a vaginal birth; the only change is receiving antibiotics through a vein during labor.

What signs of GBS should I watch for in my newborn?

In the first days to weeks, call your baby's provider right away for fever or a low temperature, trouble feeding, fast or labored breathing, or a baby who is limp, unusually sleepy, or hard to wake. Early treatment makes a big difference.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

6 Sources

Data & references

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