Group B Strep in Pregnancy: Understanding Risks, Testing and Treatment

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While many people are familiar with the kind of strep (short for streptococcus) that causes throat infections, pregnant women should know about one other type. It’s called group B streptococcus (GBS) and, if left untreated, it can cause serious complications for newborns.

Dr. Elizabeth Baker, MD, UnityPoint Health, explains why mothers should find out if they have it and how carriers can keep their baby safe during delivery.

What is Strep B?

Group B strep is a type of bacteria many people have in their normal bodily make-up. It’s commonly found in the gastrointestinal and genital tracts of healthy adults and, for the most part, doesn’t cause any harm.

“We all have bacteria that live in our intestines, mouth, genitals, skin and other organs, but only under specific circumstances can group B strep cause infections in a person,” Dr. Baker says.

For example, group B strep can pose a threat to pregnant women and newborn babies. When passed from mom to baby during childbirth, there’s a risk group B strep can lead to major health complications, like pneumonia, meningitis and other bloodstream infections in baby.

Strep B Symptoms

In general, most carriers of group B strep don’t have symptoms, and it doesn’t cause disease or illness in healthy adults. However, group B strep can cause illness in certain vulnerable populations, such as newborns, elderly and people with weakened immune systems.

How Do You Get Strep B in Pregnancy?

During pregnancy, group B strep can colonize in the genital tract — meaning, it sets up a temporary or long-term residence in that area of the body and makes its way to the urinary tract or amniotic fluid that surrounds a baby in the uterus. This can happen without signs or symptoms of infection in the mother.

Strep B can also be transmitted to the baby during childbirth as the baby passes through the birth canal.

How Common is Strep B?

According to the National Institutes of Health, it's estimated about 15-40% of people are colonized with group B strep.

If You’re Pregnant, How Do You Test for Strep B?

In pregnant women, Dr. Baker says testing is quick and simple. It consists of a swab of the vagina and rectum, and results are usually ready within a few days.

“It’s collected between 36-37 weeks of pregnancy but can be collected earlier if you have signs of preterm labor or a condition that indicates an early delivery,” Dr. Baker says. “If collected early, a negative result is only valid for five weeks, and then the test needs to be repeated.”

If the test is positive, it’s considered positive for the remainder of the pregnancy, and there’s no retesting.

“At any point during your pregnancy, if GBS is found in your urine samples, then you’re considered positive for the rest of your pregnancy without any further testing,” she says.

How to Prevent Strep B

While it’s impossible to prevent group B strep, because it occurs naturally in the body, there are ways to reduce the risk of transmitting bacteria from mother to baby during childbirth.

It’s also important to note group B strep isn’t considered a sexually transmitted infection and can be found in people who aren’t sexually active.

Group B Strep Treatment

There’s no vaccine for group B strep. Preventing the bacteria from transmitting from mother to baby during childbirth is done by giving mom antibiotics during labor.

“The first line of treatment is giving the mother penicillin through an IV during labor. Many moms ask if they can be treated earlier in pregnancy, or with a different method, but treatment earlier with an injection to the muscle or with oral antibiotics doesn’t protect baby,” Dr. Baker says.

“If you have a penicillin allergy, we have other antibiotic options that have been studied, but penicillin is still the best. This is why your doctor may ask a lot of questions regarding your reaction to penicillin, because we want to make sure we can give you the best treatment possible out of the remaining options,” she adds.

If you have a penicillin allergy, the swab is sent for extra testing as the bacteria could be resistant to other antibiotics.

If you have questions or concerns, talk to your UnityPoint Health doctor about what to expect during labor and delivery.

What Happens if You Don’t Get Tested for Strep B When Pregnant?

If a woman isn’t tested for group B strep during her pregnancy, Dr. Baker says there are many factors a doctor will review to decide if, and when, she needs to start antibiotic treatment.

“The safest plan is to make sure you attend all your prenatal appointments and get tested when your doctor recommends, so you can be treated, if needed,” she says. “The treatment is to protect the baby, as group B strep isn’t an illness in mom.”

If a pregnant woman isn’t treated for group B strep, there’s a 50% risk of transmission to the baby.

What’s the Difference Between Strep A and B?

Dr. Baker says strep A and strep B are both in the streptococcus family, but they’re different types of bacteria. Although, under a microscope, they have the same shape and arrangement.

The big difference is that strep A is most often associated with infections, like strep throat, scarlet fever and some skin conditions. It’s highly contagious and symptoms can range from mild to severe.


If you have any questions about your pregnancy, our UnityPoint Health doctors are here to support you.