Streptococcus Group B (GBS) Culture Biomarker Testing
It checks for Group B strep colonization so you can plan next steps, with convenient ordering and clear results through Vitals Vault labs.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
A Streptococcus Group B culture checks whether Group B Streptococcus (GBS, also called Streptococcus agalactiae) is present on swabs taken from areas where it commonly lives, such as the vagina and rectum. Many people carry GBS without symptoms, so the test is usually about risk planning rather than explaining how you feel.
This culture is best known for pregnancy screening because GBS colonization can be passed to a newborn during delivery. A positive result does not mean you have a sexually transmitted infection, and it does not automatically mean you or your baby are sick.
Because GBS can come and go over time, timing matters. Your result is most useful when it is collected in the window your clinician is using to make decisions about labor, delivery, or infection evaluation.
Do I need a Streptococcus Group B Culture test?
You may need a Group B strep (GBS) culture if you are pregnant and your clinician wants to know whether you are colonized late in pregnancy. Screening is commonly done in the third trimester because the goal is to predict colonization status close to delivery.
You might also be tested if you have symptoms or a clinical situation where GBS could be contributing, such as suspected urinary tract infection (when a urine culture is ordered), postpartum infection concerns, or newborn evaluation when a baby shows signs of infection. In those cases, the specimen type and the lab’s workup may differ from routine pregnancy screening.
If you have had GBS in a prior pregnancy, a prior positive culture can raise the chance of being positive again, but it does not guarantee it. A repeat culture in the recommended timeframe can help avoid unnecessary antibiotics while still protecting the baby when risk is higher.
This test supports clinician-directed decisions (for example, whether antibiotics are recommended during labor) and is not meant to be used for self-diagnosis or self-treatment.
This is a laboratory culture performed in a CLIA-certified lab; results should be interpreted with your clinician in the context of symptoms, pregnancy timing, and specimen source.
Lab testing
Order labs to measure Group B Strep Culture
from $96.97 at Quest Diagnostics
About 1 week
Schedule online — results typically within a week
Clear next steps
Guidance included, with follow-up care available
HSA / FSA
Eligible for pre-tax health spending accounts
Get this test with Vitals Vault
If you are trying to line up pregnancy screening or you need documentation of your GBS status for a clinical visit, Vitals Vault can help you order the Streptococcus Group B culture and get a clear, shareable lab report.
After your result posts, you can use PocketMD to talk through what “positive” or “negative” means for your situation, what questions to bring to your OB/GYN or midwife, and whether a repeat test makes sense based on timing.
If your clinician is also evaluating urinary symptoms, vaginal symptoms, or broader infection risk, you can use Vitals Vault to add related labs so your plan is based on a fuller picture rather than a single data point.
- Order online and test through a national lab network
- PocketMD helps you translate results into next-step questions
- Easy re-ordering if you need repeat testing closer to delivery
Key benefits of Streptococcus Group B Culture testing
- Clarifies whether you are colonized with Group B strep at the time of collection.
- Supports pregnancy planning by informing whether intrapartum antibiotics may be recommended.
- Helps avoid guessing based on past history when colonization status can change over time.
- Provides a documented result you can share with your prenatal care team or delivery facility.
- Can guide follow-up testing when symptoms suggest a different infection source or specimen type is needed.
- Improves interpretation when paired with context like gestational age, prior GBS status, and urine culture findings.
- Makes it easier to revisit the plan with PocketMD and decide whether retesting is appropriate based on timing.
What is Streptococcus Group B Culture?
A Streptococcus Group B culture is a lab test that attempts to grow Group B Streptococcus (GBS) from a collected specimen. For pregnancy screening, the specimen is typically a combined swab from the lower vagina and rectum (often called a rectovaginal swab). The lab incubates the sample and reports whether GBS is detected.
GBS is a common bacterium that can live in the gastrointestinal and genital tracts without causing symptoms. In most non-pregnant adults, colonization is not dangerous. The reason it matters in pregnancy is that GBS can be transmitted to a newborn during labor and delivery, and in some cases it can cause serious infection in the baby.
A culture is different from a general “vaginal microbiome” test or a routine urinalysis. It is targeted to identify GBS so your care team can make a prevention plan when it is clinically relevant.
Colonization vs. infection
A positive culture usually means colonization, not an active infection. Colonization means the bacteria are present on the swab site, even if you feel completely well. Infection implies symptoms and tissue involvement, and it is typically evaluated with additional clinical findings and sometimes different specimen types.
Why timing matters in pregnancy
GBS status can change, so a result from months earlier may not reflect your status at delivery. That is why screening is typically done late in pregnancy, and why your clinician may recommend antibiotics during labor based on a recent positive result or certain risk factors.
What do my Streptococcus Group B Culture results mean?
Low (not detected) GBS culture result
For this test, “low” generally maps to a negative result, meaning GBS was not detected in the specimen. This lowers the likelihood that you are colonized at the sampled sites at the time of collection, but it does not guarantee you will remain negative later because colonization can change. If you are pregnant and the sample was collected outside the recommended screening window, your clinician may still suggest repeat testing closer to delivery. If you have symptoms of infection, a negative rectovaginal screen does not rule out other causes.
In-range (negative) result in the intended screening window
An “optimal” result for routine screening is typically a negative culture collected at the right time for decision-making. In pregnancy, that usually means the result is recent enough to guide the delivery plan. Even with a negative result, your clinician may consider other factors, such as fever during labor or preterm labor, when deciding on management. The key is that the result is most meaningful when it matches the specimen type and timing your care team is using.
High (detected/positive) GBS culture result
A positive culture means GBS was detected, which usually indicates colonization. In pregnancy, this often leads to a plan for antibiotics during labor to reduce the risk of newborn infection, rather than treatment during pregnancy when you feel well. A positive result is not a sign of poor hygiene and is not typically treated like a sexually transmitted infection. If you are not pregnant, your clinician will interpret a positive result based on symptoms and specimen source, because colonization alone may not require treatment.
Factors that influence GBS culture results
Recent antibiotics can reduce bacterial growth and may contribute to a false-negative culture. Collection technique and specimen site matter, because GBS may be present in one area and not another. Timing in pregnancy is a major factor, since colonization can appear or disappear over weeks. Lab methods can vary (for example, enrichment broth use), so if your result is unexpected, it is reasonable to ask how the specimen was collected and processed.
What’s included
- Streptococcus, Group B Culture
Similar tests and related topics
Frequently Asked Questions
What does a positive Group B strep (GBS) culture mean?
A positive result means GBS was detected in the specimen, which usually indicates colonization rather than an active infection. In pregnancy, it commonly leads to a plan for antibiotics during labor to reduce the baby’s risk of infection. Outside of pregnancy, whether treatment is needed depends on symptoms and where the specimen came from.
What does a negative GBS culture mean in pregnancy?
A negative result means GBS was not detected at the sampled sites at the time of collection. It lowers the likelihood you are colonized, especially if collected in the recommended late-pregnancy window. Because colonization can change, your clinician may recommend repeat testing if the result is old or if certain risk factors arise.
When is the Group B strep test done during pregnancy?
Screening is typically performed in the third trimester so the result is recent enough to guide delivery decisions. Your clinician will choose the exact timing based on your prenatal schedule and any risk factors such as preterm labor or a prior baby affected by GBS disease.
Do I need to fast for a Streptococcus Group B culture?
No. Fasting does not affect a GBS culture result because the test is based on bacterial growth from a swab specimen, not blood chemistry.
Can antibiotics affect my GBS culture result?
Yes. Recent antibiotics can reduce bacterial growth and may contribute to a false-negative culture. If you have taken antibiotics recently, tell your clinician and consider whether the timing of the test should be adjusted.
Is Group B strep an STD?
GBS is not typically classified as a sexually transmitted infection. It is a common bacterium that can live in the gastrointestinal and genital tracts in people who have no symptoms. The main concern is pregnancy and newborn risk, not sexual transmission.
If I was GBS positive in a prior pregnancy, will I be positive again?
Not necessarily. Prior positivity increases the chance of being positive again, but colonization can change over time. A repeat culture in the recommended timeframe is the best way to know your current status and plan appropriately.