What causes gbs in pregnancy

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Last updated: April 4, 2026

Quick Answer: Group B Streptococcus (GBS) is a common bacterium that can be present in the body without causing illness. In pregnancy, it's typically detected through screening tests, and while most infected mothers and babies are asymptomatic, it can lead to serious complications like sepsis, pneumonia, or meningitis in newborns if not managed.

Key Facts

GBS colonizes the gastrointestinal and genitourinary tracts in about 20-30% of healthy adults.
It is not considered a sexually transmitted infection and is not a sign of poor hygiene.
Pregnant women are screened for GBS between 35 and 37 weeks of gestation.
Intravenous (IV) antibiotics are administered during labor to mothers who test positive for GBS.
Untreated GBS can cause severe illness in newborns, with sepsis being the most common serious complication.

Overview

Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is a type of bacteria that commonly lives in the lower digestive tract and the urinary tract of healthy people. It's estimated that between 20% and 30% of pregnant women carry GBS in their vagina or rectum. Importantly, carrying GBS does not mean a person is sick or has an infection; it is simply a colonization. Many people carry GBS without ever experiencing any health problems. However, during pregnancy and childbirth, the presence of GBS in the mother can pose a risk to the newborn.

What is Group B Streptococcus (GBS)?

GBS is a bacterium that is part of the normal flora for many individuals. It is not a sexually transmitted infection, nor is it a sign of poor hygiene. It can be present in the body intermittently or for long periods. While GBS can cause infections in people of all ages, such as urinary tract infections, skin infections, and pneumonia, the primary concern during pregnancy is its potential transmission to the baby during labor and delivery.

How is GBS Transmitted to Newborns?

The most common way GBS is transmitted to a baby is during labor and delivery. As the baby passes through the birth canal, they can come into contact with the GBS bacteria if the mother is carrying it. This can lead to early-onset GBS disease in the newborn, which typically develops within the first week of life. In rarer cases, GBS can be transmitted before labor begins if the mother's water breaks early, or even after birth through close contact.

Risks Associated with GBS in Pregnancy

While most pregnant women who carry GBS and their babies do not experience any problems, there are potential risks if GBS is transmitted to the newborn. These risks include:

Early-onset GBS disease: This occurs in the first week of life and can manifest as sepsis (a bloodstream infection), pneumonia (lung infection), or meningitis (infection of the membranes surrounding the brain and spinal cord). These conditions can be very serious and even life-threatening for newborns.
Late-onset GBS disease: This occurs from one week to several months after birth and is less common. It typically presents as sepsis or meningitis.
Complications for the mother: While less common, GBS can also cause complications for the mother, such as urinary tract infections (UTIs), chorioamnionitis (infection of the amniotic fluid and membranes), and endometritis (infection of the uterine lining after birth).

GBS Screening During Pregnancy

To mitigate the risks, pregnant women are routinely screened for GBS. This screening usually takes place between 35 and 37 weeks of gestation. The test involves taking swabs from the vagina and rectum. The samples are then sent to a laboratory to check for the presence of GBS bacteria. This screening allows healthcare providers to identify pregnant women who are carrying GBS and implement preventive measures.

Prevention of GBS Transmission

The primary method for preventing GBS transmission to newborns is the administration of intravenous (IV) antibiotics to the mother during labor. If a pregnant woman tests positive for GBS, or if she has certain risk factors (such as a previous baby with GBS disease, or preterm labor with unknown GBS status), she will be given antibiotics during labor. The antibiotics help to reduce the number of GBS bacteria in the birth canal, significantly lowering the risk of the baby becoming infected. It's crucial for women to inform their healthcare providers if they have previously tested positive for GBS in a prior pregnancy.

When are Antibiotics Not Necessary?

Antibiotics are not recommended for all pregnant women. For women who test negative for GBS, or who have not been screened and do not have other risk factors, routine antibiotic treatment during labor is generally not necessary. The decision to administer antibiotics is based on the screening results and specific clinical situations.

Important Considerations

It's essential for pregnant individuals to discuss GBS with their healthcare provider. Understanding the screening process, the potential risks, and the preventive measures is vital for a healthy pregnancy and a safe delivery for both mother and baby. Early detection and appropriate management are key to minimizing the risks associated with GBS.