GBS, or group B streptococcus, is a common bacterium that roughly 10 to 30 percent of pregnant women carry in their vaginal or rectal area. It’s usually harmless in adults, causing no symptoms at all, but it can pass to a baby during delivery and cause serious infections like sepsis, pneumonia, or meningitis. That’s why routine screening and a simple treatment plan during labor are standard parts of prenatal care.
Why GBS Matters During Pregnancy
Group B strep lives naturally in the gut and vaginal tract. Carrying it doesn’t mean you have an infection or that anything is wrong. Most women who are GBS-positive never experience any symptoms themselves. The concern is entirely about the baby. During a vaginal delivery, the bacterium can transfer to the newborn, whose immune system isn’t yet equipped to fight it off.
Without preventive treatment, a small percentage of babies born to GBS-positive mothers develop what’s called early-onset GBS disease, typically within the first week of life. The risk is low in absolute terms, but the consequences of infection can be severe, which is why universal screening is recommended rather than waiting to see if problems arise.
How Screening Works
The CDC recommends that all pregnant women get screened for GBS during the 36th or 37th week of each pregnancy. The test is quick and painless: a provider uses a swab (similar to a cotton-tipped Q-tip) to collect a sample from the vagina and rectum. The sample is sent to a lab to see whether the bacteria grow in culture, and results typically come back within a day or two.
The timing matters. GBS colonization can come and go, so a test done earlier in pregnancy may not reflect your status at the time of delivery. Testing at 36 to 37 weeks gives the most accurate snapshot of whether the bacteria will be present when you actually go into labor. A positive result from a previous pregnancy doesn’t automatically mean you’ll be positive again, so screening is repeated with every pregnancy.
What Happens If You Test Positive
A positive GBS result means you’ll receive antibiotics through an IV during labor. The medication works by reducing the amount of bacteria in the birth canal so the baby is far less likely to be exposed during delivery. Penicillin is the first-choice antibiotic for this purpose. If you have a penicillin allergy, your provider will choose an alternative based on the severity of your allergy and whether the specific strain of GBS you carry responds to other medications.
The antibiotics are given during labor, not before it. Taking oral antibiotics earlier in pregnancy doesn’t prevent GBS from returning by the time you deliver, so the IV approach during active labor is the standard protocol. Ideally, the first dose is given at least four hours before delivery to allow enough time for the medication to reach effective levels in your system.
If you’re having a planned cesarean delivery and your water hasn’t broken and labor hasn’t started, GBS antibiotics during delivery are generally not needed. The risk of transmission is tied to the baby passing through the birth canal, so a cesarean performed before labor begins bypasses that exposure.
Signs of GBS Infection in Newborns
Even with preventive antibiotics, there’s a small chance a baby can develop a GBS infection. Knowing what to watch for in the first days and weeks after birth is important. Symptoms in newborns include:
- Fever
- Difficulty feeding
- Irritability or lethargy (the baby seems limp, unusually sleepy, or hard to wake up)
- Difficulty breathing
- Bluish tint to the skin
Early-onset disease shows up within the first week, often within the first 24 to 48 hours. Late-onset disease can appear up to about three months of age and isn’t necessarily linked to exposure during delivery. If your newborn shows any of these signs, getting medical attention quickly makes a significant difference in outcomes. GBS infections in infants are treatable with antibiotics, and early detection improves the chances of a full recovery.
What GBS Doesn’t Mean
Testing positive for GBS is not a sign of poor hygiene, a sexually transmitted infection, or anything you did wrong. It’s simply part of the normal bacterial landscape that shifts in the body over time. You can be positive during one pregnancy and negative during the next, or vice versa. Carrying GBS also doesn’t affect your pregnancy itself. It won’t cause miscarriage, preterm labor, or complications for you personally. The entire focus of screening and treatment is protecting the baby during the narrow window of delivery.
The screening-and-treat approach has been one of the more effective public health strategies in obstetric care. Since routine screening and IV antibiotics during labor became standard practice, rates of early-onset GBS disease in newborns have dropped dramatically. For most women who test positive, the experience amounts to an extra IV line during labor and a healthy baby on the other side.