Group B strep (GBS) is a type of bacteria commonly found in the vaginas of many healthy women. In fact, the Centers for Disease Control and Prevention estimates that about 1 in every 4 women carries group B strep bacteria.[1]

While it's harmless to adults who have it, GBS can be transmitted to a baby during childbirth, especially without treatment, which can lead to serious health problems for the infant.

Who should be tested for group B strep?

All pregnant women are routinely tested for GBS. Why? If you're a GBS carrier, you won't have any symptoms (it isn't related to group A strep, the kind that causes throat infections) — which means you won't know you have the bacteria.

That could potentially spell trouble come delivery time, because a baby who picks up GBS during childbirth is at risk of developing a serious infection.

How is GBS treated?

The good news is that if you're given antibiotics through an IV during labor, the risk of your baby getting early-onset GBS (contracted within the first week of life) is much lower.

When left untreated, about 1 in every 200 babies born to GBS-positive mothers is affected. When antibiotics are administered, the odds go down to only 1 in 4,000.

When is the group B strep test done?

This test is now usually performed around 36 weeks of pregnancy. (Testing earlier doesn't always predict who will be carrying GBS if women deliver after 40 weeks.)

Some hospitals and birthing centers offer a rapid GBS test that can screen women during labor and provide results within the hour, in lieu of testing a few weeks earlier. Ask your practitioner if that's an option at the facility where you'll be delivering.

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Is it possible to go into labor without being tested for group B strep?

If you haven't been tested for GBS yet, your practitioner might give you IV antibiotics once you go into labor to be sure you don't pass an infection on to your baby if you have risk factors that point to group B strep, including:[2]

  • Preterm labor (including up to labor at 37 weeks if you haven't been tested for GBS)
  • Premature rupture of the membranes more than 18 hours before delivery without a diagnosis for GBS
  • Fever during labor
  • Previous positive test for GBS
  • Previous child with GBS
  • A urine test at any point in pregnancy that was positive for GBS

If for some reason your practitioner doesn't offer the GBS test during late pregnancy, be sure to ask for it.

How is group B strep testing done?

During a pelvic exam at a prenatal appointment, your practitioner will test for group B strep by taking a swab of your vagina and your rectum. The swabs will be sent to a lab for analysis.

GBS can also show up in a urine culture obtained during a prenatal checkup. If it does, it may be treated right away with oral antibiotics and again in labor with IV-administered antibiotics.

What is late-onset GBS?

Babies can, in rare cases, get late-onset GBS — which is contracted between a week and a few months after birth — either from contact with a mother carrying GBS or from someone else carrying the bacteria.[3] Late-onset group B strep isn't prevented by IV antibiotics given during labor and can also have very serious health consequences for the child.

If you tested positive for GBS and are concerned about your baby getting late-onset disease, talk to your OB/GYN and your pediatrician.

Are there any risks of being tested for GBS during pregnancy?

There are no risks associated with having the group B strep test. Playing it safe through testing — and, if necessary, treatment — means that your baby has a much better chance of being protected from a GBS infection shortly after birth.