Group B streptococcus screening

What is group B strep?

Group B streptococcus (GBS) is a kind of bacteria that many people naturally have in their intestinal tract. The bacteria may also inhabit, or "colonize," your vagina and be passed on to your baby during labor and birth. An estimated 10 to 30 percent of pregnant women carry group B strep in the vagina, rectum, or surrounding area. (This bacteria is not the same as group A strep, the type that usually causes strep throat.)

It's possible to spread group B strep through sexual contact, but it is not considered a sexually transmitted infection because your genital area may be colonized by bacteria you carry in your own gastrointestinal tract.

How is the GBS test done?

Your healthcare provider painlessly swabs the lower end of your vagina and rectum. Then the sample is sent to a lab to be grown in a culture, which will identify whether group B strep is present. Results are typically available in two to three days.

Some hospitals offer rapid group B strep tests that can be done during labor, with results available in an hour or so. But the rapid tests are not as sensitive as those that allow time for the group B strep to incubate, so the CDC, ACOG, and AAP all still recommend screening at 36 to 37 weeks.

Why do I need to be tested for group B strep when I'm pregnant?

Although group B strep is generally harmless to healthy adults, it may cause stillbirth and serious infections in babies. And getting screened for group B strep late in pregnancy – and being treated with antibiotics during labor if you test positive – greatly reduces your baby's risk of becoming infected.

That's why the U.S. Centers for Disease Control (CDC), the American Academy of Pediatrics (AAP), and the American College of Obstetricians and Gynecologists (ACOG) recommend that all pregnant women get a routine group B strep screening at 36 to 37 weeks.

You'll be treated during labor if you're at high risk for group B strep. Risk factors include:

• A positive test for group B strep at any time during your pregnancy
• A urinary tract infection (UTI) caused by group B strep or a urine culture with group B strep at any time during your pregnancy
• A previous baby with a GBS disease

Before pregnant women were routinely screened and treated, approximately 1 babies out of every 500 live births developed early-onset GBS disease, a life-threatening illness that shows up in the first week of life (most often in the first 24 hours after birth). That figure's been reduced to about 1 in 4,000 live births.

What happens if I test positive for group B strep when I'm pregnant?

A positive result means only that you carry the bacteria, not that you or your baby will become ill, even if you don't receive treatment. Try not to worry. There's only a small chance that your baby will get sick, especially if they're full-term, you don't have a fever, and your water didn't break very long before delivery.

However, getting antibiotics during labor greatly reduces the chance that your baby will be infected. For example, if you're a GBS carrier with no other risk factors, your baby's odds of getting infected are about 1 in 200 without treatment, and about 1 in 4,000 if you get treatment.

Treatment also reduces your own chances of developing a GBS infection (such as a uterine infection) during labor or postpartum.

If you test positive for group B strep, you'll be given IV antibiotics as soon as active labor begins or your water breaks, whichever comes first. If you have a C-section, you'll be given antibiotics anyway, and these antibiotics will be adequate to treat the group B strep.

Ideally, you'll start antibiotics at least four hours before you give birth. If your labor is faster than that, even a couple of hours of antibiotics reduces the risk to your baby.

What could happen to my baby if they get early-onset GBS disease?

Early-onset GBS disease can cause an infection in the blood (sepsis), pneumonia, or, less frequent, meningitis. Some babies, especially those with meningitis, will have long-term health problems, such as hearing loss or vision loss, cerebral palsy, or developmental disabilities. A small percentage won't survive.

Preterm babies have a lower survival rate than full-term babies, and those who survive are at higher risk for long-term problems from the disease.

What if I have a UTI that's caused by group B strep during pregnancy?

If a urine test shows that you have a urinary tract infection caused by a certain level of group B strep (more than 100,000 "colony forming units," or CFU), you'll be treated with oral antibiotics. CFU levels over 100,000 are also linked with preterm labor. Because antibiotics decrease bacteria, they lower this risk, in addition to treating the UTI.

Once you're done taking the antibiotics, you'll have another urine culture to make sure the infection is gone – just as with any UTI during pregnancy.

Although oral antibiotics will decrease the bacteria in your urinary tract, some bacteria may remain in your genital area or return there later.

Having group B strep in your urine is a sign that you have a lot of it in your genital tract, so you'll automatically be given IV antibiotics during labor.

What are the risks or side effects from taking antibiotics during labor?

Unless you have previously had an allergic reaction, you'll probably be given penicillin, which is the preferred drug to treat group B strep and is safe for babies. Ten percent of pregnant women who take penicillin develop mild allergic symptoms, such as a rash. Very rarely (1 in 10,000 cases), penicillin causes a severe allergic reaction that requires emergency treatment.

If you're allergic to penicillin, other antibiotics are also effective and safe for your baby. Talk to your doctor about which one is best for you.

What if I go into labor before my group B strep results are available?

If you don't know whether you're carrying the bacteria when you go into labor, you'll be treated with antibiotics if you have any of these risk factors:

• You go into preterm labor, or your water breaks before 37 weeks.
• A long delay (18 hours or more) occurs between your water breaking and your delivery.
• You develop a fever during labor (100.4 degrees Fahrenheit or higher).

If a rapid test is available and you don't have any risk factors, your provider may prefer to do the test and then treat you if the results are positive. (If the rapid results are negative but you go on to develop risk factors, you'll be treated because the rapid test may miss some GBS cases.)

Your doctor will also discuss the option of starting antibiotics if you've had group B strep in a previous pregnancy, even if you don't have any of the risk factors above.

If I test positive for group B strep, what will happen after my baby is born?

If doctors have any concern that your baby is infected with group B strep (because you have an infection at delivery or your baby has a fever), they'll start them on antibiotics immediately after delivery and order a full workup, including blood tests. If they're having difficulty breathing, a chest X-ray will be done. And if your baby has a fever that doesn't go away, a spinal tap may also be ordered.

If your baby shows no signs of infection, you can usually take them home after a day or two.

If you'd like to go home earlier than that, your baby's doctor may agree to discharge them after 24 hours as long as:

• You received antibiotics at least four hours before birth.
• You had no signs of infection during labor.
• Your baby is full-term, appears healthy, and has no other problems.
• You fully understand the doctor's instructions for observation at home.
• You have quick access to medical care.

Otherwise, your baby will remain in the hospital for at least 48 hours for observation.

If your baby is born prematurely, they'll probably have some testing done and may need to stay longer, even if you were treated during labor and they show no signs of infection. This is because premature babies are more likely to get GBS disease and tend to be sicker if they do get it.

What are the symptoms of a group B strep infection in an infant?

If you're a GBS carrier, your baby will be observed closely for signs of infection – regardless of whether you were treated with antibiotics during labor.

Studies show that 90 percent of babies who get early-onset GBS disease begin to show signs of sickness within the first 24 hours of life:

• Difficulty breathing
• Turning blue
• Unusual irritability
• Unusual limpness
• Extreme stiffness
• Feeding problems
• Lethargy (hard to wake up)
• Seizures
• Vomiting
• Fever

If you're at the hospital and notice your newborn having any of these symptoms, get help immediately.

Can my baby get a group B strep infection later?

Yes. It's possible for a baby to develop a group B strep infection after the first week, whether or not you tested positive. This usually happens within three months and is called late-onset GBS disease. In the United States, late-onset GBS disease in babies occurs slightly more often than early-onset GBS disease.

Late-onset GBS can cause the same problems as early-onset GBS and affects 3 out of every 10,000 babies. As with early-onset GBS, babies born prematurely are at higher risk. Meningitis is more common with late-onset disease.

Signs that you should contact your baby's doctor include:

• Unusual irritability
• Unusual limpness
• Extreme stiffness
• Feeding problems
• Lethargy (hard to wake up)
• Seizures
• Vomiting
• Fever

Is there any way to prevent late-onset GBS disease?

Receiving antibiotics during labor won't prevent late-onset GBS disease. Only half of babies who get late-onset GBS have mothers who are group B strep carriers, and nobody knows how the others get infected with the bacteria, so prevention is difficult.

Learn more

Inside pregnancy: Weeks 28 to 37 (video)

Prenatal tests: Overview of each trimester

Urine tests during pregnancy

Pregnancy week by week: 36 weeks

Pregnancy week by week: 37 weeks