Group B Streptococcus (GBS) in Pregnancy

Group B Streptococcus (GBS) in Pregnancy

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Group B streptococcus (GBS) is a type of bacteria that is found in 10–30% of pregnant women. A woman with GBS can pass it to her baby during labour and delivery. Most babies who get GBS from their mothers do not have any problems. A few, however, will become sick. This illness can cause serious health problems (such as, meningitis and pneumonia) and it can even be life-threatening.

What is GBS?

GBS is one of the many bacteria that live in the body and usually do not cause serious illness. It is found in the digestive, urinary, and reproductive tracts of men and women. In women, it can be found in the vagina and rectum.

GBS is not a sexually transmitted disease.

Most pregnant women who are colonized with GBS have no symptoms. A small number may develop a urinary tract infection caused by GBS. For this reason, women are tested for GBS late in pregnancy. If GBS is present, a woman will receive treatment during labour.

Testing for GBS

Women are tested for GBS between weeks 35 and 37 of gestation. In this test, a swab is used to take a sample from the woman’s vagina. This procedure is quick and should not be painful. The sample is sent to a lab where it is grown in a special substance. if you tested positive for GBS, you will need to receive treatment only in labour.

If you had a positive GBS test result in a prior pregnancy, you need to be tested again during each pregnancy. You may no longer have the bacteria. If your test result is negative, you do not need treatment during labour and delivery. If your result is positive, you will need treatment.

If you had a previous baby with GBS infection or if you had a urinary tract infection caused by GBS during this pregnancy, you are at high risk for passing GBS on to your baby during labour and delivery. A repeat test is not needed to confirm this, you will receive treatment during labour.


Penicillin is the antibiotic that is most often given to prevent GBS from being passed to your baby. If you are allergic to penicillin, you will receive a different antibiotic.

The antibiotics work only if they are given during labour or after the amniotic sac has ruptured (your “water” has “broken”), but before your baby is delivered. If treatment is given earlier in pregnancy, the bacteria may regrow and be present during labour.

Special Situations

Women who have planned a caesarean birth do not need to be given antibiotics during delivery (if their labour has not begun or their water has not broken), whether they are colonized with GBS or not. However, these women should still be tested for GBS because labour may occur before the planned caesarean birth.

Pregnant women who do not know if they are GBS positive or have not yet been tested when labour starts should be given antibiotics in specific situations

  • You go into labour at less than 37 weeks of pregnancy
  • Your water breaks 18 hours or more before delivery
  • You have a fever during labour

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