Group B Strep Testing During Pregnancy

During pregnancy, there are several routine tests designed to help protect both you and your baby. One important screening near the end of pregnancy is Group B strep testing.

Group B Streptococcus, often called Group B strep or GBS, is a type of bacteria that can live in the digestive and genital tracts. Many people carry GBS without symptoms and without knowing it. In most healthy adults, it does not cause illness. During pregnancy, however, GBS matters because it can sometimes pass to the baby during labor or delivery. The CDC notes that GBS disease is most common in newborns and that pregnant patients should be tested and receive antibiotics during labor if needed.

When Is Group B Strep Testing Done?

Group B strep testing is usually performed late in pregnancy. ACOG recommends universal vaginal and rectal culture screening between 36 weeks and 37 weeks and 6 days of pregnancy. Patients who test positive should receive appropriate antibiotics during labor.

Testing is done late in pregnancy because GBS can come and go. A result from an earlier point in pregnancy, or from a previous pregnancy, may not accurately reflect whether GBS is present near delivery.

If you are currently pregnant, WHMC provides ongoing prenatal obstetric care to help guide you through each stage of pregnancy.

What Happens During the Test?

The test is simple and quick. Your provider uses a swab to collect a sample from the vagina and rectum. It usually does not require a speculum exam. The sample is sent to a lab to check for the presence of GBS bacteria.

If the result is negative, you typically do not need GBS antibiotics during labor unless another risk factor develops. If the result is positive, your care team will plan to give antibiotics through an IV during labor.

What Does a Positive Result Mean?

A positive GBS result does not mean you have an infection, did something wrong, or have poor hygiene. It simply means the bacteria were present when you were tested.

Most people who test positive feel completely well. You generally do not need treatment right away unless GBS is found in your urine or another issue is present. Treatment is usually given during labor because that is when antibiotics can help reduce the chance of passing GBS to the baby.

How Is Group B Strep Treated During Labor?

If you test positive, antibiotics are given through an IV during labor. The CDC explains that penicillin and ampicillin are examples of commonly used beta lactam antibiotics, and other options are available for patients with severe allergies.

Be sure to tell your provider if you have ever had an allergic reaction to penicillin or another antibiotic. The type of reaction matters and helps your care team choose the safest option.

What If Labor Starts Before Testing?

If labor begins before your GBS test is done, or before the results are available, your care team will review your risk factors. These may include preterm labor, fever during labor, how long your water has been broken, whether GBS was found in your urine, or whether a previous baby had GBS disease.

Your provider will determine whether antibiotics are recommended.

Does GBS Mean I Need a C-Section?

No. A positive GBS result does not automatically mean you need a cesarean birth. Many patients who test positive for GBS have vaginal deliveries with antibiotics during labor.

If you are planning a scheduled cesarean birth, testing may still be recommended because labor or water breaking can happen before the scheduled date. You can also review WHMC’s information on the third trimester of pregnancy for more late-pregnancy guidance.

The Bottom Line

Group B strep testing is a routine and important part of prenatal care. A positive result is common and manageable. With proper screening and antibiotics during labor, your care team can help reduce risk for your newborn.

If you have questions about GBS testing or your pregnancy care plan, contact Women’s Health & Menopause Center to schedule your visit.