Everything to Know About the Group B Strep Test

Group B strep (GBS) is a form of Streptococcus bacteria often present in the digestive or urinary tracts. It's usually harmless in adults, but it can be a dangerous—even deadly—infection in a newborn.

If you're pregnant, your healthcare provider will recommend a group B strep test when you are in your 36th or 37th week. A simple test can determine if you have group B strep, which can be treated shortly before you deliver to help prevent infection in your baby.

This article explains the purpose and possible results of the group B strep test.

Purpose of a Group B Strep Test

GBS is usually found in the vagina or rectum, where it can be transmitted to an infant during vaginal delivery.

GBS is the most common cause of meningitis in newborns. It can also cause pneumonia or sepsis (an infection of the bloodstream).

The test identifies if a pregnant person has GBS so that they can be treated with antibiotics before delivery.

A pregnant person who is treated for GBS bacteria has a 1 in 4,000 chance of having a baby with GBS or will develop it soon after birth. Untreated pregnant people have a 1 in 200 chance of delivering a baby who will develop GBS.

What to Expect

You don't need to do anything to prepare for this test. They are simple tests to obtain samples that are sent to a lab for analysis. The results are sent back to your provider's office who will communicate them with you.

There are different types of group B strep tests for pregnant people and babies.

Group B Tests for Adults

• Swab test: You will lie on an exam table, and a healthcare provider will use a cotton swab to take a sample of cells from your vagina and rectum.
  
• Urine test: You'll be asked to pee in a cup. Urinate a little into the toilet before you fill the cup, which helps keep the sample sterile.

Group B Tests for Babies

• Blood test: A healthcare provider will use a small needle to take a blood sample from your baby's heel. It may sting a little.
  
• Spinal tap: A healthcare team will insert a needle into the baby's back to get a sample of spinal fluid. The area will be numbed so that the baby does not feel pain. It takes about five minutes.

Results

Positive Result in Pregnant People

If the test result is positive, a healthcare provider will give you antibiotics through an IV (intravenous line) during labor, which is more effective than taking antibiotic pills.

You will likely be given the treatment as soon as you are in active labor. Ideally, the antibiotics should be started at least four hours before delivery to give them the best chance at preventing infection in your baby.

Positive Result in Newborns

If a baby tests positive for GBS, they will be given antibiotics through an IV right away. If the baby has symptoms, healthcare providers may start them before the results are back, because GBS can cause severe illness and may be fatal in rare circumstances if infections like sepsis, pneumonia, or meningitis develop.

The antibiotics need to be given for up to 14 days, usually in a neonatal intensive care unit (NICU).

Summary

A group B strep test is recommended for pregnant people to help prevent serious infections in newborns. It is a quick and simple test. If you test positive, you'll be given antibiotics as soon as you go into labor. They will be given repeatedly every few hours until delivery, which will kill the bacteria so that it is unlikely to infect your baby. GBS infections are not usually dangerous in adults, but they can be serious or life-threatening in infants.

A Word From Verywell

Group B strep is rare in the United States because most pregnant people have testing to identify the bacteria and get treatment to protect their baby. The test is a simple procedure that can prevent serious illness in your newborn. If you have any concerns about the test, discuss them with your healthcare provider.