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Group B Strep—What is it? and Other Common Questions...

As you near the end of your pregnancy (hello, cankles!), you will be screened for Group B Strep, a common and normally harmless bacteria found in between 10-25% of women’s digestive and reproductive tracts.

Although mostly benign in adults, Group B Strep (GBS) can cause serious infections in newborns, whose immune systems are still developing. If you screen positive, you will receive intravenous antibiotics during labor to prevent you from passing Group B Strep on to your baby during delivery.



What is Group B Strep?

Group B Streptococcus(GBS), or streptococcus agalactiae, is a naturally occurring bacteria found in many men and women’s reproductive and digestive tracts.

GBS is not a sexually transmitted disease (STD). It is also not the same bacteria that causes strep throat (Group A Strep).

How common is Group B Strep?

About 1 in 4 pregnant women test positive for GBS. These women are said to be colonized with GBS.

Does being colonized with Group B Strep affect my health?

In healthy adults, being colonized by GBS is usually harmless. In a few women, GBS can cause urinary tract or bladder infections.

Why is Group B Strep a concern during pregnancy?

The main concern with carrying GBS during pregnancy is that colonized mothers can pass the bacteria to their babies during delivery.

About half of colonized mothers pass GBS on to their babies, and about 1 in 100 of those babies will develop GBS disease.

In newborns, Group B Strep infection can cause pneumonia (lung infection), meningitis (infection of the fluid and lining surrounding the brain) and sepsis (blood infection). Although most babies treated for GBS will do fine, 1 in 20 babies will die, according to the March of Dimes.

Long-term health problems can also follow infection. Of those who develop GBS meningitis, about 1 in 4 will suffer long-term cognitive effects, such as cerebral palsy, seizures, and learning disabilities.

Some studies have also linked GBS during pregnancy with a slightly increased risk of preterm labor. We still do not know, however, whether GBS causes preterm birth or simply linked with other risk factors for preterm birth.

What are my chances of passing Group B Strep on to my baby?

According to the CDC, 1 in 200 infants born to a colonized mother will develop Group B Strep disease. This drops to 1 in 4000 if the mother receives IV antibiotics during labor.

How will I know if I carry Group B Strep?

The Centers for Disease Control (CDC) recommends testing pregnant women for GBS between 35 and 37 weeks of pregnancy. This includes women who are planning to have a Cesarean section, because they could go into labor before their scheduled Cesarean.

To test for GBS, your doctor will take a swab of your vagina and rectum and then send the samples to a lab to be cultured. If you test positive, you will receive IV antibiotics during labor to reduce the chances of infecting your baby.

Does everyone need to be tested?

Women who have tested positive for GBS earlier in pregnancy or who have previously delivered a baby with GBS disease are presumed to be colonized. They do not need to be retested.

If I previously tested positive or negative for Group B Strep, why do I need to be retested?

GBS colonization can change. Some women who test positive at one point will test negative later, and vice-versa. That is why the CDC recommends screening all pregnant women for GBS shortly before labor is expected, between 35 and 37 weeks of pregnancy.

There are a couple of exceptions: If your urine tests positive for GBS at any point during your pregnancy, your colonization is presumed heavy, and the CDC does not recommend retesting. Similarly, if you previously delivered a baby with GBS disease, you will be assumed to be positive.

Will I need antibiotics during labor?

The CDC recommends that you receive intravenous (IV) antibiotics during labor:

  • If you have tested positive for GBS at any point in your current pregnancy


  • If you previously delivered a baby with a GBS disease
  • your water breaks more than 18 hours before labor begins
  • you go into labor preterm (before 37 completed weeks of pregnancy)
  • you run a fever during labor

Why do I need antibiotics during labor instead of prior to going into labor?

According to the CDC, “antibiotics help during labor only, because the bacteria can grow back quickly; doctors cannot give antibiotics before labor begins.”

Do IV antibiotics prevent all Group B Strep infections in babies?

GBS infections in babies are divided into two types:

  • Early onset disease:  symptoms occur within the first week of life (early onset disease)
  • Late onset disease: symptoms occurring after the first week but within the first three months.

Receiving IV antibiotics at least 4 hours before birth is highly effective at preventing early-onset disease, but the practice is controversial, largely because it involves treating a large percentage of pregnant women to prevent a small number of infections.

Unfortunately, antibiotics during labor do not prevent late onset disease. They also do not prevent GBS colonization during pregnancy, which has been linked with a slightly increased risk of stillbirth and preterm labor.

Looking for ways to clear GBS from your system before taking the test? Here’s what the research says about popular on  remedies.


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About Amy

Amy Kiefer is a researcher by training, and earned her Ph.D. from the University of Michigan. She currently lives in the Bay Area with her husband and three children where she writes about fertility, pregnancy, and breastfeeding. Check out her blog,, for more great evidence-based pregnancy and parenting info.


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