What is Group B Streptococcus (GBS)? - Baby Chick

What is Group B Streptococcus (GBS)?

pregnancyUpdated September 14, 2023

by Nina Spears

The Baby Chick®: Pregnancy, Birth & Postpartum Expert

Medically reviewed by Kristy Goodman

Obstetrician-Gynecologist Physician Assistant


Usually, between your 36th and 38th week of pregnancy, your care provider will do routine screening for vaginal strep B. They check whether you are positive or negative for Group B Streptococcus—found in about 10-30% of women.1 But what is Group B Streptococcus (GBS)? How does it affect you, your labor, and your baby? Here’s what you need to know.

*Disclaimer: This post is not written to be medical advice. As a birth professional myself, I get asked many of these questions. I wanted to provide the answers I have found through the years of supporting pregnant women, attending births, speaking to medical professionals and birth workers, and research. I always want to provide quality information that helps women feel more prepared before, during, and after pregnancy and birth. As always, consult with your care provider for further information.

What is GBS?

Group B Streptococcus (GBS) is a bacterial infection that naturally lives in the intestines and migrates down to the urinary tract, vagina, and/or rectum. (Group B strep is not a sexually transmitted disease.) Both men and women can be “carriers” or are “colonized” with GBS. For most people, there are no symptoms of carrying the GBS bacteria.

How Do You Get Tested for GBS?

It is now the standard in the US for all pregnant women to be routinely tested for GBS at 36 to 38 weeks during each pregnancy. (The levels of GBS can change during each pregnancy, so your results could differ from pregnancy to pregnancy. This is why they check every pregnancy regardless if you were previously positive or negative.)

Testing involves a swab of your vagina and rectum, which is then taken to a lab to see if GBS grows. Test results are usually available within 24 to 48 hours.

NOTE: Always inform your care provider if you take any new antibiotics and/or use vaginal medications. These medications may cause false-negative or false-positive results.

What Happens If I Am GBS Positive?

If you test positive for GBS, it means you are a carrier. This is nothing to be ashamed of. Nothing will change during prenatal visits (since antibiotics given before labor begins are ineffective at preventing GBS transmission).2 The difference is that you will be given antibiotics during labor to protect your baby from contracting GBS during delivery.

NOTE: If you are GBS positive, it does not guarantee your baby will also test positive and become ill.

According to the Centers for Disease Control and Prevention (CDC), if you have tested positive and are not high risk, your chances of delivering a baby with GBS are 1 in 200 babies if antibiotics are not given and 1 in 4,000 if antibiotics are given.3

If you are GBS positive, there are some risk factors you will need to watch out for because they may indicate you are at a higher risk of delivering a baby with GBS. According to ACOG, those risk factors are:4

  • Gestational age less than 37 weeks
  • Babies that have a very low birth weight
  • Prolonged rupture of membranes (>18 hours)
  • Intraamniotic infection
  • Young maternal age
  • Maternal black race
  • GBS found in the urine

How Will GBS Affect My Baby?

GBS can be passed from mother to child before or during delivery, and it can appear within hours to days after the delivery of your child. Early-onset symptoms in newborns include:5,13

  • Signs and symptoms occurring within the first week of life
  • Breathing problems
  • Fever
  • Difficult with feeding & breathing
  • Irritability or lethargy
  • Heart and blood pressure instability
  • Gastrointestinal and kidney problems
  • Blue tint to their skin

NOTE: Per the CDC, “[e]arly-onset disease used to be the most common type of GBS disease in babies. Today, because of effective early-onset disease prevention, early- and late-onset disease occurs at similarly low rates.”6

Late-onset GBS symptoms in newborns include:5

  • Signs and symptoms occur from one week to three months after delivery
  • Meningitis, which is a common complication associated with GBS infection in a newborn7

According to the CDC, GBS is a leading cause of life-threatening infections in newborns.6

How Can I Protect My Baby From Group B Strep?

The CDC recommends giving antibiotics every 4 hours (through an IV) during labor. Most doctors want you to have several rounds of antibiotics before your baby is born, but at the very least, one round 4 hours before your child’s birth. This is why most doctors do not want you to labor at home for very long so that they can make sure that you receive enough antibiotics.

The most common antibiotics given for GBS during labor are penicillin and ampicillin. If you have a penicillin allergy, you will probably be given cefazolin, clindamycin, or vancomycin since these are alternative antibiotics.

Do I Need to Be Treated for GBS If I Am Having a C-Section?

If you are GBS positive and labor has not yet begun, and/or your water has not broken, you do not need to be treated for GBS during delivery. However, if you are GBS positive and labor has begun and/or your water has broken, you will still be required to be treated for GBS even if you have a cesarean delivery.

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