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Group B Strep and Pregnancy

You might not have heard of group B streptococcus (GBS), also called "group B strep" or "baby strep." Because this infection can be harmful to babies, if you're pregnant it's important to know what it is and what to do about it.

What Is Group B Strep?

Many different types of bacteria live in the human body. Some are good for the body and others cause illness. GBS is one of the many bacteria that can live in the body and usually don't cause any problems. It's often found in the urinary, digestive, and reproductive tracts.

Because GBS can naturally come and go from the body without producing any health effects, most people who have GBS don't know that they have it and it causes no problems.

About 25% of pregnant women carry GBS. This does not mean a woman is "unclean" in any way or did anything to contract the bacteria.

What Problems Can it Cause?

Although GBS generally does not cause any problems, some people who have it get sick. Elderly people and those with chronic medical conditions, such as diabetes, cancer, and liver disease, are more likely to become ill if they have GBS. The most common problems of GBS in adults are infection of the blood (sepsis), lungs (pneumonia), skin, and bones.

In pregnant women, GBS also can cause infection of the urinary tract, placenta, womb, and amniotic fluid. Women also can pass the infection to their babies during labor and delivery.

Group B Strep and Babies

Most babies who are exposed to GBS from their mothers do not have any problems. But some can become very sick from it. Premature babies are more likely to be harmed by GBS infection than full-term babies because their bodies and immune systems are less developed.

The two types of GBS disease in babies are:

  1. Early-onset infections, which are more common and happen during the first week of life. They usually cause problems right away, within 24 hours after birth.
  2. Late-onset infections, which develop weeks to months after birth. This type of GBS disease is not well understood.

Signs and symptoms of GBS disease in newborns and infants can include:

  • fever
  • feeding problems
  • breathing problems
  • irritability or fussiness
  • inactivity or limpness
  • being unable to keep a healthy body temperature

Babies with GBS disease also can develop other serious problems, such as pneumonia, sepsis, and infection of the fluid and lining around the brain (meningitis). Meningitis is more common with late-onset GBS disease and can lead to hearing and vision loss, learning disabilities, seizures, and even death.

How Is it Diagnosed?

Pregnant women are routinely tested for GBS late in the pregnancy, usually between weeks 35 and 37. The test is simple, inexpensive, and painless. Called a culture, it involves using a large cotton swab to collect samples from the vagina and rectum. These samples are tested in a lab to see whether GBS is present. The results are usually available in 1 to 3 days.

If a test finds GBS, the woman is said to be "GBS positive." This result means only that she has the bacteria in her body — not that she or her baby will become sick from it.

GBS infection in babies is diagnosed by analyzing a sample of blood or spinal fluid. However, not all babies born to GBS-positive mothers need testing. Most healthy babies are simply watched to see if they have signs of infection.

Treatment and Prevention

Doctors have a safe and simple way to help prevent early-onset GBS disease in newborns.

First, they test the mother to see if she has GBS. If she does, she will get intravenous (IV) antibiotics during labor to kill the bacteria. Penicillin is most commonly given, but other medicines can be used if a woman is allergic to it.

It's best for a woman to receive antibiotics for at least 4 hours before delivery. This simple step greatly helps to prevent the spread of GBS to the baby.

Other women may be given antibiotics during labor, including those who:

  • go into labor before being tested for GBS (premature labor)
  • have not been tested for GBS and whose water breaks 18 or more hours before delivery
  • have not been tested for GBS and have a fever during labor
  • had a GBS bladder infection during the pregnancy
  • have had a baby before with GBS disease

Babies who get GBS disease are also treated with antibiotics. This should begin as soon as possible to help prevent problems. These babies also may need other treatments, like breathing help and IV fluids.

Giving antibiotics during labor only helps to prevent early-onset GBS disease, not late-onset disease. Because the cause of late-onset disease is unknown, no method has yet been found to prevent it. However, researchers are working to develop a vaccine to prevent GBS infection.


Because GBS comes and goes from the body, a woman should have GBS testing during each pregnancy. Women who are GBS-positive and get antibiotics at the right time during labor do well, and most don't pass the infection to their babies. They also can safely breastfeed their babies.

Date reviewed: April 2014