How Do You Contract Strep B In Pregnancy? Expert Tips

Group B Streptococcus (GBS) is a common bacterium that many adults carry naturally in their digestive tract or vagina. You do not “catch” it from someone else the way you catch a cold. During pregnancy, GBS can be passed to a baby during labor, which is why doctors test for it late in pregnancy. The key point is that GBS colonization is not an infection you contract from a specific source — it is a normal part of your body’s bacteria that can come and go without symptoms.

What is Group B Strep?

Group B Streptococcus, often called GBS or strep B, is a type of bacteria that naturally lives in the intestines, rectum, or vagina of about 1 in 4 healthy adults. Most people never know they carry it because it causes no symptoms. In pregnancy, the concern is not for the mother but for the baby during childbirth. If a mother carries GBS at the time of delivery, the baby can be exposed as it passes through the birth canal. This exposure can, in rare cases, lead to serious infection in the newborn.

GBS is not the same as group A strep, which causes strep throat. It is also not a sexually transmitted infection. Carrying GBS is normal and does not mean you are sick or have done anything wrong. In fact, many women who test positive for GBS during one pregnancy may test negative in another pregnancy — the bacteria come and go on their own.

How Do You Contract Strep B In Pregnancy?

You do not contract GBS from an outside source. Instead, you become colonized — meaning the bacteria take up residence in your body without causing illness. Colonization can happen at any point in life and often goes unnoticed. There is no specific activity, sexual partner, or hygiene practice that causes GBS colonization. It is simply part of the normal bacteria that live in the human body.

Testing for GBS is a standard part of prenatal care in the United States. The CDC and the American College of Obstetricians and Gynecologists recommend that all pregnant women be tested for GBS between 36 and 37 weeks of pregnancy. The test is a simple swab of the vagina and rectum. If the result is positive, you will receive intravenous (IV) antibiotics during labor to reduce the chance of passing the bacteria to your baby. This treatment is very effective at preventing newborn infection.

Who is at Higher Risk of GBS Colonization?

Any pregnant woman can carry GBS, but some factors are linked to higher colonization rates. These include being Black, having a body mass index over 30, and being younger than 20. However, even without these factors, you can still be colonized. The most important risk factor for passing GBS to a baby is having a positive test at 36–37 weeks and not receiving antibiotics during labor.

Other risk factors that increase the chance of newborn infection include labor starting before 37 weeks, a fever during labor, or having a previous baby with GBS disease. If your water breaks more than 18 hours before delivery, the risk also rises. In these situations, doctors may give antibiotics even if you have not been tested or if your test result is unknown.

How is GBS Diagnosed in Pregnancy?

Diagnosis is straightforward. Between 36 and 37 weeks of pregnancy, your doctor or midwife will swab your lower vagina and rectum. The sample is sent to a lab to see if GBS grows in a culture. This is the standard screening test. Results usually come back in a few days. Some hospitals also use a faster test called a PCR test if a woman goes into labor before being screened, but the culture test is the gold standard.

It is important to know that GBS colonization can be intermittent. You could test negative at 36 weeks but become colonized later. However, current guidelines do not recommend retesting after a negative result because the risk of a late conversion is low, and the benefits of universal retesting have not been proven.

How is GBS Treated During Labor?

GBS is not treated with antibiotics during pregnancy itself. Treatment is given only during labor, and it is given intravenously (through an IV). The standard antibiotic is penicillin or ampicillin. If you are allergic to penicillin, your doctor will choose a different antibiotic, such as cefazolin, clindamycin, or vancomycin, depending on the specific allergy and your GBS strain. The goal is to give antibiotics at least four hours before delivery to reduce the bacteria in the birth canal enough to protect the baby.

If you have a scheduled Cesarean section and you have not gone into labor, you generally do not need antibiotics for GBS because the baby is not passing through the birth canal. However, if your water breaks or labor begins before the scheduled C-section, you may still need antibiotics. Your doctor will decide based on your specific situation.

What Are the Risks to the Baby?

Most babies born to mothers who carry GBS are perfectly healthy. Without antibiotic protection during labor, about 1–2% of babies will develop an early-onset GBS infection within the first week of life. This infection can cause pneumonia, sepsis, or meningitis. With IV antibiotics during labor, the risk drops dramatically — by about 80%.

Late-onset GBS infection (occurring after the first week of life and up to age 3 months) is not prevented by labor antibiotics. It can come from sources other than the mother, such as from the environment. Late-onset GBS is rare, affecting about 0.3–0.5 per 1,000 live births. Parents should watch for signs of illness in a newborn: fever, difficulty breathing, extreme fussiness, or poor feeding. If any of these occur, seek medical attention immediately.

Can You Reduce Your Risk of GBS Colonization?

No reliable evidence shows that diet, probiotics, or hygiene practices can permanently clear GBS from your body or prevent colonization. Some studies have looked at probiotics, but results are mixed, and no large trials have confirmed benefit. The best prevention against newborn infection is universal screening and giving IV antibiotics during labor to women who test positive. This approach is proven and widely used.

There is no need to avoid certain foods, take special supplements, or douche (which is not recommended during pregnancy anyway). Douching can actually disrupt normal vaginal bacteria and may increase the risk of other pregnancy complications. The most important step is to attend your prenatal appointments and get the routine GBS test at 36–37 weeks. If you are positive, remind your healthcare provider when you go into labor so they can start antibiotics promptly.

Common Myths About GBS

Myth: GBS is an STD. Not true. GBS is part of the normal body flora and is not sexually transmitted. Having GBS does not mean you or your partner has an infection. Myth: A previous baby with GBS means all future babies will be affected. Not necessarily. Each pregnancy is different. If you had a baby with early-onset GBS, you will be offered antibiotics during labor in future pregnancies, even if you test negative. Myth: GBS causes miscarriage or stillbirth. GBS is rarely linked to pregnancy loss. Most stillbirths and miscarriages have other causes. Myth: You can treat GBS with oral antibiotics during pregnancy. Oral antibiotics do not reliably clear GBS from the birth canal, and they can increase antibiotic resistance. IV antibiotics during labor are the standard.

What Happens After Delivery?

If you received antibiotics during labor, your baby will be monitored for signs of infection for at least 48 hours after birth. Many hospitals will keep the baby in the nursery or your room for observation. If your baby shows no problems after 48 hours, no further treatment is needed. If your baby was born before 37 weeks, had a fever, or had prolonged rupture of membranes, the observation period may be longer, and blood tests may be done.

If you did not receive antibiotics during labor and your baby develops symptoms, immediate treatment with IV antibiotics can be very effective. Outcomes for early-onset GBS are generally good with prompt care. The key is early recognition. Parents should trust their instincts — if a newborn seems “off,” it is always worth calling the pediatrician.