What Is Group B Strep in Pregnancy?

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Group B streptococcus, commonly known as group B strep or GBS, is a common form of bacteria carried in the intestines or lower genital tract of the body. Carrying group B strep is usually harmless, but pregnant people will be tested for GBS bacteria in their third trimester because group B strep could infect a baby during labor. GBS infection can make your baby very unwell, but with early treatment, most babies will make a full recovery.

Read on to learn more about GBS, what a positive test means for you and your baby, and how this common pregnancy concern is treated.

Cropped shot of a mature female doctor using a laptop while having a discussion with her pregnant patient in her office

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What Is Group B Strep?

Group B streptococcus (GBS) is a common form of bacteria that lives in the body, usually in the digestive tract, rectum, or vagina.

According to the Centers for Disease Control and Prevention (CDC), approximately 25% of pregnant people carry group B strep.

Many people carrying the bacterium don’t know it. GBS in adults usually doesn’t have any symptoms, although it can cause some minor infections, like bladder or urinary tract infections (UTI).

While GBS may not be harmful to healthy adults and pregnant people, it can be very harmful to babies. Babies can become infected during childbirth as the bacteria are often found in the vagina and rectum.

What Are GBS Bacteria?

GBS bacteria live in the body naturally. GBS is not a sexually transmitted infection, nor does it spread through food, water, or anything that people might come into contact with.

What Could GBS Mean for My Baby?

Babies can come into contact with GBS during labor and delivery. The majority of these babies will not become ill. However, if you carry GBS, there is a small chance that your baby will develop a GBS infection and become seriously ill, or even die.

According to the CDC, GBS may be fatal in up to 6% of babies who are infected.

Types of GBS Infection

There are two main types of GBS infection a baby can acquire. They are:

Early-onset: With early-onset GBS, a baby typically gets sick within 12–48 hours after birth or up to the first 7 days. Early-onset GBS can cause severe problems, such as:

  • Inflammation of the covering of the brain or spinal cord (meningitis)
  • Infection of the lungs (pneumonia)
  • Infection in the blood (sepsis)

Late-onset: This can occur from the first week through the first three months of life. Late-onset disease is serious and can cause meningitis. Contact your baby’s healthcare professional right away if your baby has any signs or symptoms of infection, including:

  • Low energy
  • Irritability
  • Poor feeding
  • High fever

Premature babies, low birth weight babies, and those who have a compromised immune system are at a higher risk of developing an infection.

Most babies who develop GBS infection recover without complications, but severe cases do occur. Severe cases of GBS can cause hearing or vision loss. The infection also is associated with cerebral palsy.

Additionally, if there are complications from the infection, such as respiratory distress, sepsis, or pneumonia, group B strep can lead to long-term neurological problems and even death.

Testing for GBS

The American College of Obstetricians and Gynecologists (ACOG) recommends a screening test for GBS during the third trimester, between 36 and 38 weeks.

During your prenatal examination, the healthcare provider will take a swab of the vagina and rectum to send out for laboratory testing. The swab test for GBS is quick, pain-free, and poses no risk to the fetus.

If your results reveal that GBS is present, you will receive antibiotics through an intravenous (IV) line once labor has started.


The only way to help protect your baby from a GBS infection if you test positive is to be given antibiotics during labor.

If GBS is present in your body and you don’t get antibiotic treatment during labor, you have a one in 200 chance of passing the infection to your baby. In cases in which an antibiotic has been administered during labor, the chances of a baby developing GBS decrease to just one in 4,000.

The following will not prevent you from passing GBS to your baby:

  • Taking oral antibiotics
  • Taking antibiotics before labor begins
  • Using birth canal washes with the disinfectant chlorhexidine


If you test positive for GBS, you will be given IV antibiotics, usually a form of penicillin, such as ampicillin, during labor. If you know you’re GBS positive, don’t delay getting to the hospital once your water breaks or your labor starts. To be most effective, you should begin receiving the antibiotics at least four hours before you deliver.

In some cases, you may be automatically given antibiotics during labor without testing for GBS. Antibiotics may be given without testing if:

  • You had a previous child with GBS infection.
  • You had tested positive for GBS bacteria in your urine at any point during your pregnancy.
  • Your GBS status is not known when you go into labor, and you have a fever.
  • Your GBS status is not known, and you go into labor before 37 weeks' gestation.
  • Your GBS status is not known, and it has been 18 hours or more since your water broke.
  • Your GBS status for this pregnancy is not known, but you tested positive for GBS in a past pregnancy.

If you are allergic to penicillin (you may be offered allergy testing to confirm), your healthcare provider will notify the lab when testing for GBS and give you an appropriate alternative.

What if I Plan to Have a Cesarean Birth?

Pregnant people who have a cesarean birth do not need to be given antibiotics for GBS during delivery if their labor has not started and the amniotic sac has not ruptured (their bag of waters has not broken). But you should still be tested for GBS because labor may happen before a cesarean birth. If the test result is positive, the baby may need to be monitored for GBS after delivery.

Treatment for Newborns

Babies testing positive for GBS infection will be given IV antibiotics. But the best treatment is prevention.

Early-onset GBS has dropped 80% in babies between the early 1990s and 2010 due to the widespread administering of late-pregnancy testing and the use of antibiotics in GBS-positive people during labor.

The decline is believed to be a result of healthcare providers waiting until labor to start antibiotics. Waiting until labor is preferred because treating earlier in the pregnancy could allow GBS to clear and then return before delivery.

Coping with a GBS Diagnosis

If your GBS test was positive, try not to worry too much as the risk to your baby is greatly reduced with antibiotics during labor. Prepare yourself for labor following your positive test by:

  • Telling your healthcare provider if you have any drug allergies, especially if you are allergic to penicillin or other antibiotics.
  • Talking to your practitioner or midwife about your birth plan. If you were planning a home birth, you may need to change your plans due to the need for IV antibiotics during labor. 
  • Letting your healthcare provider know if you develop any symptoms of urinary tract infection or have a fever.
  • Calling your practitioner’s office when your water breaks or you begin to feel regular contractions. Go to the hospital right away. Let the hospital staff know you tested positive for GBS, as they'll ideally want to get your antibiotics started at least four hours before your baby is born.


Group B strep is usually harmless, but pregnant people will be tested for GBS bacteria in their third trimester because it can sometimes infect a baby during labor.

A Word From Verywell

It can be scary to hear that you tested positive for group B strep and that your baby has a chance of becoming ill. But you should take comfort in knowing that GBS prevention guidelines have proven effective in protecting babies.

Prepare yourself for labor by talking to your healthcare provider or midwife about your birth plan and make sure to get to the hospital as soon as you can when labor starts. Remember, GBS is very common and complications for newborns are very rare.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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