Most pregnant women don’t hear the words “Group B Strep” until they’re somewhere in the third trimester. A swab gets done at a routine appointment, the result comes back positive, and suddenly there are questions that weren’t on anyone’s radar a few weeks earlier.
A positive Group B Strep result is one of those findings that sounds alarming but, in most cases, is very manageable. Understanding what it actually means — and what doesn’t change about your birth plan — makes a significant difference in how you approach the end of pregnancy.
What Is Group B Strep?
Group B Streptococcus (GBS) is a type of bacteria that naturally lives in the digestive tract, rectum, and vagina of many healthy adults. It’s not a sexually transmitted infection, and it doesn’t mean something went wrong. It’s simply part of the normal bacterial environment of the body for a significant percentage of people.
Outside of pregnancy, GBS rarely causes any problems for healthy adults. The concern in pregnancy is that the bacteria can be passed to a baby during labor and delivery, where it can cause serious infection in a newborn whose immune system isn’t yet equipped to fight it.
How Common Is It?
Roughly 1 in 4 pregnant women — about 25% — carry Group B Strep in their vagina or rectum at any given time. Carrying the bacteria is called being “colonized,” and it doesn’t mean you have an infection. Most women with GBS have no symptoms at all.
Colonization also isn’t permanent. A woman can test positive at one point in pregnancy and negative at another, or vice versa. This is why the timing of the test matters — it’s done late in pregnancy specifically to reflect what’s present around the time of delivery.
When and How Is the Test Done?
GBS screening is a standard part of prenatal care and is typically done between 36 and 37 weeks of pregnancy. Your provider collects a simple swab from the vaginal and rectal area — it takes only a few seconds and doesn’t require a speculum or internal exam.
The sample is sent to a lab, and results are usually back within a day or two. The timing matters: testing too early means the result may not accurately reflect GBS status at delivery.
In some situations, women arrive in labor without a recent GBS test on file — for example, if labor starts early or prenatal records aren’t available. In those cases, providers use clinical risk factors to determine whether antibiotics are appropriate.
What a Positive Result Actually Means
Testing positive for GBS means the bacteria were present in your vagina or rectum at the time of the swab. It does not mean you have an infection, and it doesn’t mean your baby will automatically be exposed.
The risk of a baby contracting GBS during delivery — even without any treatment — is actually relatively low. But GBS infection in a newborn can be serious, which is why treatment during labor is strongly recommended when a mother tests positive. The goal is to reduce even a low risk to as close to zero as possible.
What Happens During Labor If You’re GBS Positive
The standard treatment is IV antibiotics given during labor — typically penicillin, which is safe during pregnancy and has a long track record of effectively preventing GBS transmission to the baby. The first dose is ideally given at least four hours before delivery to provide maximum protection.
The antibiotics are given through an IV line, not taken as a pill, because they need to reach the baby through the placenta. They’re given during active labor only — not weeks in advance, because treating GBS earlier doesn’t prevent it from being present again at delivery.
If you have a penicillin allergy, your provider will choose an appropriate alternative antibiotic based on your allergy history and the sensitivity of the bacteria identified in your test.
Factors That Increase the Baby’s Risk
Even among GBS-positive mothers, certain circumstances increase the chance of the bacteria passing to the baby and causing illness. These include:
- Preterm labor — babies born before 37 weeks have less developed immune systems
- Prolonged rupture of membranes — waters breaking more than 18 hours before delivery
- Fever during labor
- A previous baby who developed a GBS infection
- GBS detected in the urine during this pregnancy (which indicates a heavier bacterial load)
When any of these factors are present, the indication for IV antibiotics is even stronger, regardless of when the GBS swab was done.
What If You’re Having a C-Section?
If you’re having a planned cesarean section and your membranes are still intact at the time of surgery, the risk of GBS passing to the baby is very low. In this situation, IV antibiotics specifically for GBS are generally not required.
However, if your water breaks before the planned C-section, or if labor begins before surgery, the same guidelines for GBS treatment apply. Your provider will make this call based on what’s happening at the time.
GBS Found in Urine During Pregnancy
Sometimes GBS is discovered not through the routine late-pregnancy swab but through a urine culture done earlier in pregnancy. When GBS shows up in the urine, it indicates a higher level of colonization than a simple vaginal swab would typically detect.
In this case, your provider will usually prescribe a short course of oral antibiotics to clear the active urinary tract involvement, and you’ll automatically be given IV antibiotics during labor regardless of whether a swab at 36–37 weeks is positive or negative.
Can GBS Cause Problems for the Mother?
For most healthy pregnant women who are simply carriers, GBS doesn’t cause symptoms or illness. The primary concern is transmission to the baby.
In some cases, GBS can cause a urinary tract infection during pregnancy, which is treated with antibiotics when found. GBS can also occasionally cause postpartum uterine infection, which is treated the same way. If you develop signs of infection — fever, unusual discharge, or abdominal tenderness — after delivery, let your provider know right away.
What About the Baby After Delivery?
With IV antibiotics during labor, the risk of a baby developing GBS infection is dramatically reduced. When GBS infection does occur in a newborn, it falls into two categories: early-onset (within the first week of life, usually the first 24 to 48 hours) and late-onset (one week to three months after birth).
IV antibiotics during labor prevent early-onset GBS effectively. Late-onset GBS, which is less common, is not prevented by intrapartum antibiotics — it may come from other sources in the environment.
Signs of GBS infection in a newborn include fever, difficulty feeding, breathing problems, irritability, or unusual limpness. Any of these in the first days or weeks of life should be reported to the baby’s pediatrician immediately.
Frequently Asked Questions
- If I tested positive for GBS in a previous pregnancy, will I test positive again?
Not necessarily. GBS status can change between pregnancies and even throughout the same pregnancy. A positive result in one pregnancy doesn’t mean you’ll test positive in the next, which is why screening is repeated fresh in each pregnancy. That said, a previous positive result is noted as a risk factor, and it will inform how closely your provider monitors your results.
- Will being GBS positive change my birth plan?
In most cases, not significantly. A GBS-positive result means you’ll have an IV line during labor for antibiotics, but it doesn’t change your ability to have a vaginal birth, use pain relief options, move around during labor, or follow most other preferences in your birth plan. Your delivery remains your delivery — the antibiotics are a precaution, not a complication.
- Can I do anything to prevent testing positive for GBS?
There is currently no reliable way to prevent GBS colonization before the test. Probiotics and dietary changes are sometimes discussed, but the evidence supporting them is not strong enough for clinical recommendations. What matters most is that the screening test gets done at the right time so your provider knows your status and can plan accordingly.
- Is GBS the same as Group A Strep — the kind that causes strep throat?
No. Group A Streptococcus and Group B Streptococcus are related but different bacteria. Group A causes strep throat and some skin infections. Group B colonizes the gut and genital tract and is the one screened for in pregnancy. They’re handled differently and require different treatment approaches.
- What if I go into labor before I’ve been tested?
If you arrive in labor without a GBS result on file — because labor started early or because the test wasn’t completed in time — your provider will use a risk-based approach to determine whether antibiotics are recommended. Factors like gestational age, how long your membranes have been ruptured, and whether you have a fever during labor all inform that decision.
Conclusion
A positive GBS result catches a lot of women off guard, but it’s one of the most routine findings of late pregnancy — and one that’s very effectively managed with IV antibiotics during labor.
The test exists precisely because the consequence of not knowing can be serious for a newborn. Finding out gives your provider the information to protect your baby from the start of labor through delivery.
If you have questions about your GBS result or what it means for your delivery, bring it up at your next prenatal visit. At KEM Health, we walk patients through what each test result means and make sure you go into labor with a clear understanding of your care plan.