Group B strep (GBS) is a common bacterium that about 1 in 4 pregnant women carry in the vagina or rectum, usually without any symptoms. Most babies born to GBS-positive mothers are perfectly healthy, but in rare cases the bacteria can pass to the baby during birth and cause serious infections including blood infections (sepsis), pneumonia, and meningitis. Globally, early-onset GBS disease occurs in roughly 0.41 per 1,000 live births, making it uncommon but potentially dangerous when it does happen.
How GBS Reaches the Baby
The most common route is direct contact during vaginal delivery. As the baby moves through the birth canal, bacteria living in the mother’s vagina or rectum can enter the baby’s airways, eyes, or skin. From there, the bacteria can reach the bloodstream or lungs.
In some cases, GBS doesn’t wait for delivery. The bacteria can travel upward through the cervix and into the uterus before labor begins, a process called ascending infection. Once GBS reaches the amniotic cavity or placental membranes, it can trigger inflammation of those membranes, a condition linked to preterm birth and, in severe cases, stillbirth. This ascending route is one reason that antibiotics given during labor don’t prevent every case of GBS disease.
Early-Onset Disease: The First Week
Early-onset GBS disease strikes within the first seven days of life, and most affected newborns show signs on the day they are born. The infection typically takes the form of sepsis or pneumonia. Warning signs include:
- Difficulty breathing or rapid, labored breaths
- Fever
- Difficulty feeding or refusing to eat
- Lethargy, meaning the baby is limp, unusually sleepy, or hard to wake
- Bluish skin color, especially around the lips or fingertips
- Irritability that seems out of proportion
Because symptoms often appear within hours of birth, most early-onset cases are caught while the baby is still in the hospital. Babies identified as high risk may be monitored more closely during those first 24 to 48 hours.
Late-Onset Disease: Week One Through Three Months
Late-onset GBS disease develops between 7 and 89 days after birth. It occurs at a lower rate, around 0.26 per 1,000 live births globally. The symptoms are similar to early-onset disease, but meningitis (infection of the membranes surrounding the brain and spinal cord) is more common in this form. Late-onset disease also tends to develop more gradually, which can make it harder to spot immediately.
The source of infection isn’t always the mother. Babies can pick up GBS from caregivers or from the environment, particularly in healthcare settings. This means that even babies born by cesarean section or to mothers who tested negative can occasionally develop late-onset disease. Antibiotics given during labor do not prevent late-onset infections.
Which Babies Face Higher Risk
Several factors raise the chance that a baby will develop GBS disease. Prematurity is one of the biggest: babies born before 37 weeks have immune systems that are less equipped to fight off infection, and they are more likely to be exposed if the mother’s membranes rupture early. Other risk factors include:
- Low birth weight
- Prolonged rupture of membranes (water breaking many hours before delivery)
- Maternal fever during labor of 100.4°F (38°C) or higher
- Heavy GBS colonization in the mother, including GBS found in urine during pregnancy
- A previous baby who had GBS disease
- Maternal age under 20
Black and African-American women have higher rates of GBS colonization and GBS-related newborn disease, though the reasons are not fully understood and likely involve a combination of biological and systemic healthcare factors.
How Screening and Prevention Work
In the United States, all pregnant women are screened for GBS between 36 and 37 weeks of pregnancy with a simple vaginal and rectal swab. The test result remains valid for about five weeks. If you test positive, the standard approach is to receive IV antibiotics during labor, ideally at least four hours before delivery. This doesn’t eliminate GBS from your body, but it dramatically reduces the number of bacteria the baby encounters during birth.
Real-world data shows this approach is 86% to 89% effective at preventing early-onset GBS disease. For mothers who deliver preterm and receive antibiotics at least four hours before birth, the effectiveness drops to about 78%. These are strong numbers, but they aren’t 100%, which is why newborns are still monitored for symptoms even after antibiotics are given.
Women who go into labor before their screening results are available, or whose GBS status is unknown, typically receive antibiotics as a precaution if they deliver before 37 weeks. If your pregnancy extends past 41 weeks and your original screen was negative, a repeat swab is reasonable since colonization status can change.
Long-Term Effects on the Baby
Most babies who develop GBS disease recover fully with prompt antibiotic treatment in the hospital. Sepsis and pneumonia caught early generally respond well. Meningitis carries more serious risks. Some babies who survive GBS meningitis experience lasting effects including hearing loss, vision problems, or developmental delays. The severity depends on how quickly treatment begins and how extensively the infection affected the brain.
GBS can also affect babies before birth. When ascending infection triggers severe inflammation of the placental membranes, it can lead to preterm delivery with all its associated complications, or in rare cases, stillbirth. These outcomes are uncommon but represent the most serious end of the spectrum.
Breastfeeding With GBS
Being GBS-positive does not mean you need to stop or avoid breastfeeding. Breast milk contains antibodies that may offer some protection, though the exact role of those antibodies in preventing GBS disease is still not well understood. Current guidance suggests that GBS testing of breast milk is only worth considering in specific situations, such as when a preterm baby in intensive care develops a recurrent GBS infection, or when the mother has mastitis. For the vast majority of GBS-positive mothers, breastfeeding is safe and encouraged.