Late in pregnancy, your OB/GYN may talk with you about a routine test called group B strep screening. If you have never heard of it before, the name can sound concerning. The good news is that group B streptococcus (often called GBS) is common, the screening test is simple, and there are well-established steps that can help protect newborns.
Understanding why the test is offered and what the results mean can make this part of prenatal care feel much less intimidating.
What is group B strep?
Group B strep is a type of bacteria that many healthy people carry naturally in their bodies. In women, it is most often found in the digestive tract, vagina, or rectum. Carrying GBS usually does not cause symptoms or make someone feel ill.
GBS is not a sexually transmitted infection, and it is not the same bacteria that causes strep throat. The American College of Obstetricians and Gynecologists explains that about one in four pregnant women carries GBS.
During labor and delivery, GBS can sometimes be passed to a baby. Most babies are not affected, but in rare cases the bacteria can cause a serious newborn infection. That is why screening and treatment during labor are important parts of routine prenatal care.
When does GBS screening happen?
GBS screening is typically done late in pregnancy, usually around weeks 36 and 37. A simple swab is used to collect samples from the vagina and rectum, which are then sent to a laboratory.
The test is quick and should not be painful. It does not involve a speculum exam, needles, or a blood draw.
Screening is done during each pregnancy because GBS bacteria can come and go in the body over time. A positive result in one pregnancy does not automatically mean that you will test positive in a later pregnancy. The Centers for Disease Control and Prevention recommends screening during every pregnancy, even when a cesarean birth is planned.
What does a positive result mean?
A positive GBS test does not mean that you are sick or that you have done anything wrong. It simply means that the bacteria were present when the sample was collected.
If your test is positive, your care team will usually recommend antibiotics through an IV after labor begins. This treatment helps lower the chance of early GBS infection in the newborn.
In most situations, antibiotics are not given weeks before delivery because the bacteria can return. Treatment is most effective when given during labor. Penicillin is commonly used, but there are alternatives for patients with a penicillin allergy. Be sure your OB/GYN knows about any medication allergies, including what type of reaction you have had in the past.
There are some circumstances in which your physician may recommend antibiotics during labor without waiting for a current screening result. For example, this may be appropriate when there is a history of a prior baby with GBS disease or when GBS was found in the urine during the current pregnancy. Your care team will review your individual history and make recommendations based on your situation.
What if my result is negative?
A negative result means GBS was not found in the sample collected at that time. Your physician will document the result in your prenatal record so your labor and delivery team has the information they need.
Even with a negative screening result, always contact your maternity care team if you think you are in labor, your water breaks, or you have concerns about changes in your pregnancy. Your team can advise you on the right next step based on your symptoms and pregnancy history.
Questions you may want to ask
As your screening date approaches, consider asking:
- When will my GBS test be done?
- How and when will I receive my results?
- What happens if my test is positive?
- What should I do if I have a penicillin allergy?
- Will my result be included in my hospital record?
- Does my delivery plan affect GBS treatment?
Prenatal care is designed to help you understand what to expect at each stage of pregnancy. GBS screening is one more routine step that gives your care team information to help protect you and your baby during delivery.
For more patient information, visit ACOG’s Group B Strep and Pregnancy FAQ or the CDC’s GBS screening resource.
This article is for general educational purposes and is not a substitute for individualized medical advice. Please speak with your OB/GYN about your personal pregnancy care and any questions about GBS screening.
