“Strep in pregnancy” almost always refers to Group B Strep (GBS), a common bacterium that lives naturally in the vagina or rectum of 10% to 30% of pregnant women in the United States. It rarely causes problems for the mother, but it can pass to the baby during delivery and cause serious infection. That’s why routine screening and a straightforward treatment during labor have become standard practice.
Less commonly, “strep in pregnancy” can mean a Group A Strep infection, the same bacteria behind strep throat. Group A Strep is a very different situation, and far less common, but it carries its own risks. This article covers both.
Group B Strep: What It Is and Why It Matters
Group B Strep is not a disease you catch from someone. It’s a normal part of the bacterial community living in your body, particularly in the digestive and genital tracts. Carrying GBS doesn’t mean you’re sick, and most women who test positive have zero symptoms. The bacteria can come and go over time, which is why screening happens late in pregnancy rather than early.
The concern isn’t really about you. It’s about your baby. During vaginal delivery, GBS can transfer to the newborn as the baby passes through the birth canal. A newborn’s immune system isn’t equipped to fight off certain bacterial infections, and GBS is the leading cause of serious early infections in newborns. About 45% of all confirmed bloodstream infections in full-term newborns within the first week of life are caused by GBS.
How and When You’re Screened
The American College of Obstetricians and Gynecologists recommends universal GBS screening between 36 and 37 weeks of pregnancy. The test is simple and painless: your provider uses a swab (like a Q-tip) on the vagina and rectum, then sends the sample to a lab. Results typically come back within a day or two.
This screening window exists for a practical reason. GBS colonization can fluctuate, so testing too early might not reflect your status at the time of delivery. Testing at 36 to 37 weeks gives the most accurate picture of whether the bacteria will be present when labor begins.
There’s one exception to this timeline. If GBS is found in your urine at any point during pregnancy (even at a routine prenatal visit), you’re automatically considered GBS-positive for delivery purposes and won’t need the late-pregnancy swab. GBS in the urine, even without symptoms, signals heavier colonization and is treated as a marker for vaginal and rectal carriage.
What GBS in Urine Means
Finding GBS in a urine culture during pregnancy is fairly common and has specific implications depending on the bacterial count. A high count (100,000 or more colony-forming units per milliliter) is considered a positive result and is typically treated with antibiotics at the time it’s found, because untreated urinary bacteria in pregnancy can progress to a urinary tract infection or kidney infection in 20% to 35% of cases.
A lower count suggests the bacteria migrated from the vaginal or rectal area into the urine sample. It doesn’t require immediate antibiotic treatment, but it still flags you as GBS-positive for labor. Regardless of the count, GBS in urine at any level during pregnancy means you’ll receive antibiotics through an IV when labor begins.
Risks to the Baby
Newborn GBS disease comes in two forms. Early-onset disease appears within the first six days of life, with the vast majority of cases (about 95%) showing up within the first 48 hours. Late-onset disease develops between 7 and 89 days after birth and is not prevented by antibiotics given during labor.
Early-onset GBS most commonly causes bloodstream infections. About 9.5% of affected babies develop meningitis (infection of the membranes around the brain). These are serious conditions, but the overall risk is low. Before widespread screening and treatment, the rate was roughly 1 in 400 births among GBS-positive mothers. With IV antibiotics during labor, that drops to about 1 in 4,000.
Late-onset disease is less well understood. It can come from the mother, from caregivers, or from the hospital environment after birth. No current prevention strategy exists for late-onset GBS, and more than half of all newborn GBS cases now fall into this category.
What Happens During Labor if You’re Positive
If your screening comes back positive, you’ll receive antibiotics through an IV once labor starts. This is called intrapartum prophylaxis. The antibiotics work best when given at least four hours before delivery, giving the medication enough time to reach effective levels in your body and in the fluid surrounding the baby.
The treatment applies regardless of whether you’re planning a vaginal delivery. You won’t be given antibiotics before labor begins, because taking them early doesn’t reduce the risk to the baby. The timing matters: the bacteria need to be suppressed specifically during the window when the baby is being born.
If you have a penicillin allergy, your provider has alternatives. For low-risk allergies (a rash years ago, for example), a related antibiotic is usually safe. For confirmed high-risk allergies where anaphylaxis is a concern, other options are available. Most people with a documented penicillin allergy can actually receive the first-line treatment safely, so your provider may ask detailed questions about your allergy history.
Group A Strep in Pregnancy
Group A Strep is a completely different bacterium. It causes strep throat, skin infections, and in rare cases, severe invasive infections. Unlike GBS, Group A Strep is not part of normal body flora. It spreads from person to person and causes active illness.
In pregnancy and especially in the postpartum period, Group A Strep poses a unique danger. Postpartum women have a 20-fold higher rate of invasive Group A Strep infection compared to non-pregnant women. This increased vulnerability comes from the physical changes of delivery: an open cervix, vaginal tears or surgical incisions, and the temporary suppression of immune function that pregnancy causes.
Invasive Group A Strep can cause puerperal sepsis, a blood infection that was historically one of the leading causes of maternal death. In the United States, the annual incidence is about 6 per 100,000 live births, with roughly 2% of those cases being fatal. Globally, puerperal sepsis still causes approximately 75,000 maternal deaths per year, concentrated in regions with limited access to antibiotics and intensive care.
Strep throat during pregnancy itself is generally manageable with standard antibiotics. The serious concern is invasive infection, particularly in the days immediately following delivery. High fever, rapidly worsening pain, or signs of infection in the first few days postpartum warrant immediate medical attention.
GBS-Positive but Delivering by Planned C-Section
If you’re GBS-positive and have a scheduled cesarean delivery before labor starts and before your water breaks, the risk of transmitting GBS to your baby is very low. In this scenario, antibiotics for GBS are generally not needed because the baby doesn’t pass through the birth canal where the bacteria reside. However, if labor begins unexpectedly or your membranes rupture before the surgery, you’ll receive the standard IV antibiotics.
What a Positive Test Doesn’t Mean
Testing positive for GBS doesn’t mean you have an infection. It means the bacteria are present, which is a normal finding in up to a third of women. It doesn’t reflect hygiene, sexual activity, or anything you did or didn’t do. GBS status can change from one pregnancy to the next, which is why screening happens with every pregnancy.
A positive result also doesn’t mean your baby will get sick. Even without treatment, the vast majority of babies born to GBS-positive mothers are fine. The antibiotics given during labor are a precaution that reduces an already small risk by about tenfold, making serious newborn infection very rare.