FAQ105, July 2019

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Group B Strep and Pregnancy

What is group B streptococcus?

Group B streptococcus (GBS) is one of the many bacteria that live in the body. It usually does not cause serious illness, and it is not a sexually transmitted infection (STI). Also, although the names are similar, GBS is different from group A streptococcus, the bacteria that causes “strep throat.”

Why is group B streptococcus a concern for pregnant women?

In women, GBS most often is found in the vagina and rectum. This means that GBS can pass from a pregnant woman to her fetus during labor. This is rare and happens to 1 or 2 babies out of 100 when the mother does not receive treatment with antibiotics during labor. The chance of a newborn getting sick is much lower when the mother receives treatment.

How can group B streptococcus affect a newborn?

Even though it is rare for a baby to get GBS, it can be very serious when it happens. Babies who get GBS may have early-onset or late-onset disease.

What is early-onset disease?

With early-onset disease, a baby typically gets sick within 12 to 48 hours after birth or up to the first 7 days. Early-onset disease can cause severe problems, such as

  • inflammation of the covering of the brain or spinal cord (meningitis)
  • infection of the lungs (pneumonia)
  • infection in the blood (sepsis)

A small number of babies with early-onset disease die even with immediate treatment.

What is late-onset disease?

With late-onset disease, a baby gets sick between a week to a few months after birth. The disease is usually caused by contact with the mother after delivery if she is infected. But it can come from other sources too, such as contact with other people who have GBS.

Late-onset disease also is serious and can cause meningitis. In newborns, the signs and symptoms of meningitis can be hard to spot. Contact your baby’s health care professional right away if your baby has any signs or symptoms of disease, including

  • lack of energy
  • irritability
  • poor feeding
  • high fever

Will I be tested for group B streptococcus?

Yes, pregnant women are screened for GBS as part of routine prenatal care. The test for GBS is called a culture. It is now done between 36 and 38 weeks of pregnancy. In this test, a swab is used to take a sample from the vagina and rectum.

What if the test result is positive?

If the results show that GBS is present, most women will receive antibiotics through an intravenous (IV) line once labor has started. This is done to help protect the fetus from being infected. The best time for treatment is during labor. Penicillin is the antibiotic that is most often given to prevent early-onset disease in newborns. While treatment with antibiotics during labor can help prevent early-onset GBS disease in a baby, this treatment does not prevent late-onset disease.

What if I am allergic to penicillin?

If you are allergic to penicillin, tell your health care professional before you are tested for GBS. You may have a skin test to determine the severity of your allergies. If needed, other antibiotics can be used.

Are there times when antibiotics are given without testing first?

In some cases, women are automatically given antibiotics during labor without testing for GBS. Antibiotics may be given without testing if

  • you had a previous child who had GBS disease
  • you have GBS bacteria in your urine at any point during your pregnancy
  • your GBS status is not known when you go into labor and you have a fever
  • your GBS status is not known and you go into labor before 37 weeks
  • your GBS status is not known and it has been 18 hours or more since your water broke
  • your GBS status for this pregnancy is not known but you tested positive for GBS in a past pregnancy

What if I plan to have a cesarean birth?

Women who have a cesarean birth do not need to be given antibiotics for GBS during delivery if their labor has not started and the amniotic sac has not ruptured (their water has not broken). But these women should still be tested for GBS because labor may happen before a cesarean birth. If the test result is positive, the baby may need to be monitored for GBS disease after birth.


Amniotic Sac: Fluid-filled sac in a woman’s uterus. The fetus develops in this sac.

Antibiotics: Drugs that treat certain types of infections.

Bacteria: One-celled organisms that can cause infections in the human body.

Cesarean Birth: Birth of a fetus from the uterus through an incision (cut) made in the woman’s abdomen.

Fetus: The stage of human development beyond 8 completed weeks after fertilization.

Group B Streptococcus (GBS): A type of bacteria that many people carry normally and can be passed to the fetus at the time of delivery. GBS can cause serious infection in some newborns. Antibiotics are given to women who carry the bacteria during labor to prevent newborn infection.

Intravenous (IV) Line: A tube inserted into a vein and used to deliver medication or fluids.

Meningitis: Inflammation of the covering of the brain or spinal cord.

Pneumonia: An infection of the lungs.

Prenatal Care: A program of care for a pregnant woman before the birth of her baby.

Rectum: The last part of the digestive tract.

Sepsis: A condition in which infectious toxins (usually from bacteria) are in the blood. It is a serious condition that can be life threatening. Symptoms include fever, rapid heart rate, breathing difficulty, and mental confusion.

Sexually Transmitted Infection (STI): An infection that is spread by sexual contact. Infections include chlamydia, gonorrhea, human papillomavirus (HPV), herpes, syphilis, and human immunodeficiency virus (HIV, the cause of acquired immunodeficiency syndrome [AIDS]).

Vagina: A tube-like structure surrounded by muscles. The vagina leads from the uterus to the outside of the body.

If you have further questions, contact your obstetrician–gynecologist.

FAQ105: This information was designed as an educational aid to patients and sets forth current information and opinions related to women’s health. It is not intended as a statement of the standard of care, nor does it comprise all proper treatments or methods of care. It is not a substitute for a treating clinician’s independent professional judgment. Please check for updates at to ensure accuracy.

Copyright July 2019 by the American College of Obstetricians and Gynecologists. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, posted on the internet, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher.

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