Group B Strep

The Information You Need About Strep Infections

Almost everyone we know has had strep throat at some point or another in their lives. A Group B Strep (GBS) infection is different, though. Group B Strep is a type of bacteria that can be found in the vagina or rectum of pregnant women. It is commonly found in the vagina, intestines and rectum. If you test positive for this type of bacteria, you are said to be colonized with it.

As a part of your routine prenatal care, your physician or midwife will test you to see if you are colonized. The test is normally performed between the 35th to 37th week of pregnancy. The test involves swabbing the vagina and rectum with a cotton swab that looks like a Q-tip. The cotton swab is placed in a vial and sent to the lab. It normally takes 48 hours for the test to be completed. If the test result is negative, you are not colonized with the bacteria. If the test is positive, you are colonized with Group B Strep. The results of the test are good for approximately five weeks.

There are two types of GBS infections:

  • Early Onset. Most babies that have an early-onset Group B Strep infection will begin to show signs within the first day of life; however, early-onset infections can occur within the first week of life.
  • Late Onset. Babies with late-onset Group B Strep infections show no signs of infection during the first week of life. Symptoms begin to appear between the second week of life up to three months of age.

Prevention, Detection And Treatment

First things first: GBS is completely harmless to you, but it does need to be treated so your baby does not suffer any complications. Approximately 10 to 40 percent of women are colonized with Group B Strep.1 So if you are diagnosed with it, you don't have to feel alone: many women have been in the same position you are in now.

Group B Strep can be passed to your baby by traveling upward from the vagina into the amniotic fluid (fluid that surrounds the baby) after your water breaks. In some cases, the bacteria can reach baby before the membranes are ruptured (water breaks).

The American College of Obstetricians and Gynecologists, the Centers for Disease Control and Prevention, and the American Academy of Pediatrics all recommend the same course of action if you test positive for Group B Strep: you should receive an antibiotic when you are in labor. The antibiotic is given to prevent infection in your baby. Research has shown that giving intravenous antibiotics to Group B Strep-positive mothers while they are in labor greatly reduces the transmission of the bacteria to their babies. In order for the antibiotic to be effective, it should be started at least four hours before baby is born.1 The type of antibiotic that you will receive depends on whether or not you have any allergies to specific medications.

Quick Notes

If your Group B Strep test was positive and you plan to deliver your baby by cesarean section, and you are not in labor, and your water did not break, you do not need to receive antibiotics to prevent the bacteria from reaching your baby.1

If you delivered a baby in the past who had an infection caused by Group B Strep, you should receive intravenous antibiotics while in labor with each pregnancy that follows. 1

If you develop a fever of 100.4 or higher while you are in labor, and the results of your Group B Strep culture are unknown, you should receive antibiotics to reduce the risk of the bacteria reaching your baby. 1

If you would go into labor before the Group B Strep culture is done, the swab should be performed in the labor and delivery unit, and you should receive intravenous antibiotics.

Common Medications For Mothers With GBS

The most common antibiotic is penicillin G, 5 million units for the first dose, followed by 2.5 to 3 million units every four hours until delivery, or ampicillin, 2 grams for the first dose, followed by 1 gram, given by intravenous infusion, every four hours until delivery.

If you are allergic to penicillin, your doctor may prescribe clindamycin, which is normally given every eight hours until your baby is born. Before clindamycin is given, your physician, or midwife, should check to make sure that the bacteria is susceptible (not resistant) to clindamycin. This is done by reviewing the susceptibility report from the laboratory that performed the testing for Group B Strep. If the bacteria are resistant to clindamycin, another antibiotic, vancomycin, may be given.

Note: If you have an allergy to penicillin, your physician may ask you about the type of reaction that you had in the past. The information will help to classify the reaction as low-risk, (rash or itching) or high-risk (swelling of your tongue or throat, or difficulty breathing). If your reaction was considered to be low-risk, your physician may order a different form of penicillin. If the reaction is considered to be high-risk, no form of penicillin antibiotics will be given.

What Happens If You Go Into Labor Before The Test Or Antibiotic Treatment Is Complete?

Not every baby that is born to a mother who did not receive antibiotics before delivery will become ill. For example, if you experience a fast labor, you may give birth to your baby before an antibiotic can be given, or before the antibiotic is effective. Remember, in order for the antibiotics to be effective, the first dose should be started at least four hours before the birth of your baby.

If your Group B Strep culture was positive, but you did not receive antibiotics before your baby was born, or the baby was born within four hours after the first dose of antibiotic was started, the latest guidelines from the Centers for Disease Control and Prevention (2010) recommends the following:

If the gestational age of baby is 37 weeks or greater, and your membranes were ruptured (water was broken) for less than 18 hours before delivery, no additional tests are necessary for your baby (such as blood work). However, some experts recommend that baby should have a blood test (CBC with differential and platelet count) when they are between six and 12 hours old. Your baby should remain in the hospital for a full 48 hours after birth. This is necessary for the hospital staff and baby's pediatrician to monitor the baby for any signs of infection.2

If the gestational age of baby is less than 37 weeks' gestation, or your membranes were ruptured longer than 18 hours, your baby should receive blood work that includes: CBC with differential, blood culture and platelet count. This lab work may be drawn soon after baby's birth, or when baby is between six and 12 hours old. Your baby should remain in the hospital for a full 48 hours after birth.2

  1. Baker, C. Neonatal group B streptococcal disease: Prevention. (2016). UptoDate. Retrieved from
  2. Puopolo, K., Baker, C. (2016). Management of the infant whose mother has received group B streptococcal chemoprophylaxis. UptoDate. Retrieved from