Streptococcus agalactiae, otherwise known as Group B Strep (GBS), is a bacteria that approximately 20-25 percent of pregnant women have in their vagina and rectum. Carrying this bacteria does not mean that you acquired a sexually transmitted infection or practice poor hygiene. Plainly put, GBS can be temporarily present in all women but only becomes significant when you are pregnant because of what it can potentially mean for you and your baby.

GBS can be passed to a baby as he or she passes through the birth canal at the time of delivery. Of those babies who are exposed (and whose moms received no antibiotics in labor against GBS), anywhere from 5-50 percent of babies will actually become infected themselves with GBS. It is more likely that a baby will become infected if the mother has certain risk factors, such as having a fever in labor or giving birth preterm.

GBS infections in newborns can lead to infections in the lungs, bloodstream, and nervous system, which can have severe consequences. To decrease the numbers of newborns with these complications, all pregnant women are now screened for GBS to see if they are positive.

This screening is usually done between 35–37 weeks of pregnancy via a simple swab of the vagina and rectum. Additionally, if a woman has GBS in her urine culture (which is done at the beginning of her prenatal care and any other time a concern for a urinary tract infection arises), this swab will be skipped, and it will be assumed she is still a carrier. Women who go into preterm labor or whose bag of water breaks early will also be screened before the 35- or 37-week mark. Lastly, women who are having a scheduled C-section need not be treated during their delivery but should still be screened in case they do deliver vaginally.

With the problems that GBS infections can cause in newborns, you may wonder if having GBS is a reason to have a scheduled C-section. This is definitely not the case! Luckily, the treatment for GBS is simple: your doctor or midwife will order IV antibiotics to be given during your labor to decrease the chance of transmission. The drug of choice is usually penicillin, but if you are allergic, an alternative will be used. The goal is to have the antibiotics in at least four hours before you deliver.

These measures have worked: since universal screening and treatment in labor has gone in to effect, the prevalence of GBS infection is now only 0.5 per 1,000 live births! This is why a C-section is definitely not necessary for moms who are positive for GBS.

It is important to note that women colonized with GBS can occasionally have issues, too. Having a large amount of GBS present in your urine can cause symptoms similar to a urinary tract infection, which can be treated with oral antibiotics. Having GBS can also slightly increase your risk for a uterine infection at the time of delivery or after. However, there is no good data that suggests treating all GBS positive women before delivery decreases these complications. There are some myths of alternative treatments (such as garlic and colloidal silver) out there for women who test positive, but there is no data to back up these practices, and they are not recommended.

Reviewed by Dr. Jen Lincoln, April 2020


  • Roughly 20-25 percent of pregnant women are colonized with GBS.
  • GBS can pass to a baby as he or she goes through the birth canal, and this risk can be reduced by antibiotics in labor.
  • All pregnant women are now screened for GBS during their pregnancy.


  1. Gabbe SG et al. Obstetrics: Normal and Problem Pregnancies. Maternal and perinatal infection—bacterial.
  2. The American College of Obstetricians and Gynecologists. FAQ#105: Group B streptococcus and pregnancy.


Tell us who you are! We use your name to make your comments, emails, and notifications more personal.

Tell us who you are! We use your name to make your comments, emails, and notifications more personal.