Pregnancy involves many routine tests, and the GBS test in pregnancy is one that is usually performed toward the end of the third trimester. If your doctor or midwife has recommended Group B Streptococcus screening, you may have questions about what GBS is, whether a positive result is dangerous, and what happens during labor.
The reassuring news is that GBS screening is a simple and routine part of prenatal care. Being GBS-positive does not mean that you are sick or that something is wrong with your pregnancy. The purpose of screening is to identify people who carry the bacteria so that appropriate precautions can be taken during labor to reduce the baby’s risk of serious early-onset GBS infection.
Let’s look at everything you need to know about the GBS test during pregnancy.
What Is Group B Strep (GBS)?
Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is bacteria that can normally be found in the digestive and genital tracts.
Many healthy adults carry GBS without experiencing any symptoms. GBS colonization can also change over time, meaning a person may test positive at one point and negative at another. This is one reason screening is performed during every pregnancy rather than relying on a result from a previous pregnancy.
Having GBS does not mean:
- You have poor hygiene
- You have done anything wrong during pregnancy
- You have a sexually transmitted infection
- You are sick
- Your baby will definitely develop an infection
In most pregnant people, GBS colonization does not cause illness. The main concern is that GBS may spread from the mother to the newborn around the time of delivery. Most babies who are exposed do not become infected, but a small number can develop a serious infection.
Why Is GBS Screening Important During Pregnancy?
GBS can cause serious infections in newborns, particularly during the first week of life. This is called early-onset GBS disease.
A newborn with GBS infection can develop conditions such as:
- Sepsis, a serious bloodstream infection
- Pneumonia, which can affect breathing
- Meningitis is an infection of the protective membranes surrounding the brain and spinal cord.
Most babies who develop early-onset GBS disease become ill very soon after birth, which is why prevention during labor is so important.
The good news is that screening allows healthcare professionals to identify pregnant people who carry GBS and provide antibiotics during labor when indicated.
When Is the GBS Test Done in Pregnancy?
In current U.S. guidance, routine GBS screening is recommended during 36 0/7 to 37 6/7 weeks of pregnancy. This timing helps make the result more representative of your GBS status close to delivery because colonization can change over time.
The test is generally recommended during every pregnancy, even if you were GBS-negative or GBS-positive during a previous pregnancy.
What If GBS Is Found in Your Urine During Pregnancy?
If GBS is detected in your urine during pregnancy, your healthcare provider may consider you to have an indication for antibiotics during labor without requiring the usual late-pregnancy screening culture.
GBS found in the urine can also require treatment during pregnancy depending on the amount of bacteria and whether you have symptoms. Your healthcare provider can determine whether treatment is necessary.
Another reason you may receive antibiotics during labor without a current positive screening test is if you previously had a baby who developed GBS disease. Your healthcare provider will review your individual history and determine the appropriate plan.
How Is the GBS Test Performed?
The GBS test is quick and does not require a blood draw.
A healthcare professional uses a sterile swab to collect a sample from the required areas.
- The lower vagina
- The rectal area
The sample is sent to a laboratory for testing. It usually takes just a short time and does not require fasting or any special preparation.
Some healthcare settings may also offer self-collected swabs, depending on local practice and available testing methods.
You can normally return to your usual activities immediately after the test.
Does the GBS Test Hurt?
For most people, the GBS swab is not painful, although you may experience brief pressure or mild discomfort.
If you are nervous about the examination, tell your doctor or midwife beforehand. They can explain each step and help you feel more comfortable.
How Long Does It Take to Get GBS Test Results?
The time required depends on the laboratory and the testing method used. Your healthcare provider or laboratory can tell you when to expect your result.
If you go into labor before your GBS result is available, your medical team can use other factors—such as gestational age, fever during labor, duration of membrane rupture, and previous GBS history—to determine whether antibiotics are recommended.
What Does a Positive GBS Test Mean?
A positive GBS test means that GBS was detected in the sample.
It does not mean that you have an active infection or that your baby is infected.
It also does not mean you need to take antibiotics for the remainder of your pregnancy simply because the screening culture was positive. The main preventive treatment for a positive screening result is usually intravenous antibiotics during labor.
Being GBS-positive is relatively common. Estimates vary by population, but GBS colonization is found in a substantial proportion of pregnant people.
So if your result is positive, there is no reason to feel embarrassed or blame yourself. GBS can naturally come and go from the body.
How Is GBS Treated During Labor?
When antibiotics are indicated, they are given through an IV during labor.
The purpose is to reduce the amount of GBS exposure around the time of birth and lower the baby’s risk of developing early-onset GBS disease.
Which Antibiotic Is Usually Used?
Penicillin is the preferred antibiotic for intrapartum GBS prevention. Intravenous ampicillin is an acceptable alternative.
The choice of antibiotic can be different for someone with a penicillin allergy.
For people with a reported penicillin allergy, the medical team considers the type and severity of the previous reaction. Depending on the allergy history, options may include cefazolin, clindamycin, or vancomycin. Clindamycin is used only when the GBS strain has been shown to be susceptible to it.
If you have been told that you are allergic to penicillin, make sure your obstetric team knows about the allergy and what happened when you previously received the medication.
Does GBS Treatment Need to Start 4 Hours Before Delivery?
You may hear that antibiotics need to be given for at least four hours before birth.
Four hours of appropriate IV antibiotic exposure is considered optimal for prevention, but labor or medically necessary obstetric care should not be delayed solely to reach the four-hour mark.
Antibiotics should be started as soon as possible after labor begins or when they are otherwise indicated.
This distinction is important because babies can sometimes be born quickly, leaving less than four hours for treatment. Even then, the medical team should not delay necessary delivery simply to complete four hours of antibiotics.
Can GBS Be Treated Before Labor?
Routine treatment of a positive vaginal or rectal GBS screening result with antibiotics before labor is generally not the strategy used to prevent early-onset newborn disease.
The reason is that GBS can return or recolonize after treatment. Antibiotics given during labor are used because this is the period when the newborn is most likely to be exposed.
However, GBS found in the urine may require treatment during pregnancy depending on the circumstances. Your doctor will assess your results and determine if treatment is required.
What If You Are Having a Planned C-Section?
If you have a planned cesarean birth before labor begins and while your membranes are still intact, GBS-specific intrapartum antibiotic prophylaxis is generally not required, even if your GBS test is positive.
However, routine GBS screening is still recommended because labor or rupture of membranes can occur before the planned cesarean.
A cesarean birth also involves its own standard surgical antibiotic recommendations, which are separate from GBS-specific prevention.
What Happens to the Baby After Birth?
A positive maternal GBS result does not automatically mean that your newborn is sick or needs antibiotics.
After birth, the healthcare team considers several factors, including:
- Whether you received antibiotics during labor
- How long the membranes were ruptured
- Whether your baby was born prematurely
- Whether you had a fever during labor
- Whether the baby shows any signs of infection
A healthy newborn may simply receive routine care and observation when the appropriate preventive antibiotics were given.
If a baby shows signs of illness or has additional risk factors, the pediatric team may recommend further evaluation or treatment.
What Symptoms Should Parents Watch for in a Newborn?
Although most babies born to GBS-positive mothers remain healthy, parents should know the warning signs of serious newborn infection.
Get urgent medical care if a newborn develops symptoms such as the following.
- Difficulty breathing or unusual breathing patterns
- Poor feeding
- Unusual sleepiness or difficulty waking
- Fever or unusually low temperature
- Irritability or unusual behavior
- Changes in skin color
- Signs that the baby is becoming seriously unwell
Infections in newborns can worsen rapidly, so seek medical advice without delay if you are concerned.
Conclusion
Being told that you need a GBS test can feel like one more thing to think about as your due date approaches, but the test itself is quick and straightforward. More importantly, the information it provides can help your healthcare team take effective steps to protect your baby from serious early-onset GBS infection.
If your result is positive, try not to panic. GBS carriage is common, and a positive result does not mean that you or your baby is sick. Your maternity team can make a plan for labor, including the appropriate use of IV antibiotics when indicated.
If you have questions about your GBS result, penicillin allergy, planned cesarean delivery, or what to expect if labor starts before your screening result is available, discuss them with your obstetrician, midwife, or other qualified maternity-care professional.
