Pregnancy comes with a list of check-ups and tests, each designed to monitor the health of the mother and baby. As you approach the final weeks of pregnancy, your doctor may recommend a test you may not have heard much about: Group B Streptococcus, or GBS, screening.
The name may sound worrying, but being GBS-positive does not mean that you are sick. Group B Streptococcus is a type of bacteria that can naturally live in the digestive and genital tracts. Around 1 in 4 pregnant women carry GBS, usually without experiencing any symptoms. The reason doctors pay attention to it during pregnancy is that the bacteria can occasionally pass to the baby during labour and cause a serious infection in a newborn.
The good news is that a simple screening test can identify whether GBS is present, and appropriate antibiotics during labour can significantly reduce the risk of early-onset GBS infection in the baby.
What Is Group B Streptococcus?
Group B Streptococcus is one of the many types of bacteria that can naturally live in the human body. In women, it is most commonly found in the vagina and rectum.Having GBS does not necessarily mean there is an infection that needs treatment. Most women who carry the bacteria have no symptoms and remain healthy.
GBS is also not considered a sexually transmitted infection. It is simply a type of bacteria that can be present naturally in the body.
The concern during pregnancy is different. During labour, GBS can sometimes pass from the mother to the baby. Although this transmission does not usually cause problems, a small number of newborns can develop serious GBS disease.
Why Does GBS Matter During Pregnancy?
For most mothers, carrying GBS does not cause any health problems. The concern is primarily about the newborn.If a baby develops early-onset GBS disease, symptoms usually appear within the first week after birth and often within the first 12–48 hours. The infection can cause serious conditions such as pneumonia, sepsis or meningitis.
The risk of a baby developing GBS disease is relatively low, but the consequences can be serious. This is why screening and appropriate management during labour are an important part of prenatal care.
When Is the GBS Test Done?
Current RCOG guidance recommends routine GBS screening between 35-37 weeks of pregnancy. Testing during this period helps provide a result that is relevant close to the time of delivery.
The test is straightforward. A healthcare professional uses a swab to collect samples from the vagina and rectum. The sample is then sent to a laboratory to determine whether GBS bacteria are present.
It is not a blood test, and the screening does not usually require complicated preparation.
What Happens If the Test Is Positive?
A positive GBS result does not mean that something is wrong with the pregnancy. It simply means that GBS bacteria were detected at the time of screening.If GBS is detected, antibiotics are usually given through an intravenous line after labour begins. The purpose is to reduce the amount of bacteria the baby may be exposed to during birth and lower the risk of early-onset GBS disease.
The timing of the antibiotics is important. Treating GBS earlier in pregnancy does not reliably eliminate the bacteria because it can naturally return. Giving antibiotics during labour targets the period when the baby is most likely to be exposed.
Does a Positive GBS Result Mean You Need a C-Section?
No. Being GBS-positive does not automatically mean that you need a caesarean birth.
If you go into labour or your water breaks, your healthcare team will take your GBS status into account and provide antibiotics during labour when appropriate.
If a planned caesarean is performed before labour begins and before the amniotic sac has ruptured, GBS-specific antibiotic prophylaxis is generally not required. However, routine screening is still recommended because labour or rupture of membranes may occur before the planned procedure.
Your obstetrician will advise you according to your individual pregnancy and delivery plan.
What If You Are Allergic to Penicillin?
Penicillin is commonly used to prevent early-onset GBS disease during labour. If you have a known penicillin allergy, make sure your obstetrician is aware of it.Depending on the nature and severity of the allergy, your healthcare team can determine which antibiotic is appropriate. Your allergy information may also be considered when the laboratory processes the GBS sample.
What If You Had GBS During a Previous Pregnancy?
A previous GBS-positive result does not necessarily mean that you will carry GBS during your current pregnancy. GBS colonisation can change over time, which is why screening is generally performed during each pregnancy.
However, certain situations may mean that antibiotics are recommended during labour without waiting for a new screening result. These include having previously delivered a baby who developed GBS disease or having GBS bacteria detected in the urine during the current pregnancy.
Your obstetrician can explain what your previous history means for your current pregnancy.
Can GBS Be Prevented?
There is currently no routine method to permanently eliminate GBS colonisation before delivery. The bacteria can naturally come and go.Instead, medical care focuses on screening during pregnancy and providing antibiotics during labour when indicated. This approach helps reduce the risk of early-onset GBS disease in newborns.
It is also important to follow your antenatal care schedule and tell your doctor about previous GBS results, GBS found in your urine, or a previous baby who developed GBS infection.
What About the Baby After Birth?
Even when a mother carries GBS, most babies do not develop an infection. However, newborns who develop GBS disease can become seriously ill.
Parents should seek immediate medical attention if a newborn shows concerning symptoms such as poor feeding, unusual irritability, lack of energy or fever. These symptoms can have many causes, but newborn illness should always be assessed promptly.
It is also worth knowing that antibiotics given during labour are designed to prevent early-onset GBS disease. They do not prevent every form of GBS infection that may occur later in infancy.
A Simple Test That Can Make a Difference
GBS screening may seem like just another test towards the end of pregnancy, but it has an important purpose. Since most women who carry GBS have no symptoms, testing provides information that cannot reliably be obtained simply by asking how a mother feels.
A positive result should not be a reason for panic. It gives your healthcare team an opportunity to plan appropriate care during labour and reduce the risk of early-onset infection in your newborn.
If you are approaching the final weeks of pregnancy, ask your obstetrician when your GBS screening is due and what the result could mean for your delivery plan.
Frequently Asked Questions
Can I have GBS without knowing it?
Yes. Most women who carry GBS do not experience symptoms. Screening is therefore important because you generally cannot tell whether you carry the bacteria based on how you feel.
Is GBS the same as the bacteria that causes strep throat?
No. Group B Streptococcus is different from Group A Streptococcus, which is associated with conditions such as strep throat.
If I test positive, will my baby definitely get GBS?
No. Most babies born to mothers who carry GBS do not develop GBS disease. Screening identifies mothers who may benefit from antibiotics during labour, which helps reduce the risk of early-onset infection.
