How Long Do GBS Test Results Take? | What To Expect

Group B strep test results are usually available within 24 to 48 hours after your provider sends the swab sample to the laboratory.

The third trimester has a way of piling on the lab slips. Blood work, glucose screens, and somewhere in the stack is a swab for group B strep. It feels routine until you realize the result determines whether you’ll get antibiotics during labor. Sitting around waiting for a phone call that may or may not come adds its own low-grade stress to an already full plate.

Knowing the typical turnaround time helps take the guesswork out of that wait. The short answer is that most people hear back within a day or two after the sample reaches the lab. A few factors can shift that window by a few hours, and it helps to know what they are so you aren’t left refreshing your patient portal over the weekend.

What The GBS Test Actually Checks

Group B strep is a type of bacterial colonization that can live in the digestive tract and lower genital tract. It comes and goes naturally — you can test positive in one pregnancy and negative in the next. Carrying GBS is not an infection or a sexually transmitted disease, and it usually causes no symptoms in adults.

The test itself is straightforward. A provider takes a swab of the vagina and then the rectum, which takes about a minute in the exam room. The sample is sent to a lab, where the lab grows a culture to see whether GBS bacteria are present.

Because the results guide whether you receive intravenous antibiotics during labor to protect the baby, the CDC recommends screening between 35 and 37 weeks of pregnancy. The 87% predictive value of the 35- to 37-week screen holds up well if delivery occurs within five weeks of the test.

Why The Waiting Window Can Shift By A Few Hours

Most of the time the lab runs the culture overnight and reports results the next day. But the 24-to-48-hour window exists for several practical reasons, and knowing them can save you from anxiously checking your phone too early.

• Lab schedules and location: Urban hospital labs may process samples daily, while smaller or rural labs may batch them. Batching can add a few hours of lag time.
• Penicillin allergy flags: If you have a history of severe penicillin allergy, the lab may run additional tests to see which alternative antibiotic will work. That workup can add 24 to 72 hours on top of the culture time.
• Weekend and holiday timing: Samples collected late Friday may sit in the queue until Monday. If your swab is on a Thursday, results typically land sooner than if it’s on a Friday afternoon.
• Rapid tests during labor: If you arrive at the hospital without a documented result, some providers use a quick PCR test that returns in about one to two hours. It is less sensitive than the culture but useful when time is short.

The most reliable way to estimate your personal turnaround time is to ask the office or lab when they expect to send the report. Many practices automatically post negative results to the patient portal and only call for positive ones, which can change how quickly you hear something.

The Official Guidelines On Screening Timing

Group B strep can appear and disappear without warning, which is why timing the test matters. Per the CDC testing recommendation, the ideal window for screening is late in the third trimester, specifically between 35 weeks and 37 weeks. Testing earlier than that lowers how well the result predicts colonization at delivery.

A positive result means the lab detected GBS at the time of the swab. It does not mean you are ill or that your baby will get sick. It means your provider will likely recommend IV antibiotics — usually penicillin — once labor starts to reduce the chance of passing the bacteria to the baby during birth.

A negative result means no GBS was detected in that sample. You will not need antibiotics for GBS prevention during labor unless a urine culture earlier in pregnancy had already flagged GBS. Even with a negative screen, the bacteria can show up later, but the risk is smaller.

The majority of in-office screenings fall into the 24-to-48-hour lane. Knowing whether your lab runs cultures daily or on a batch schedule can narrow the window even further for your specific situation.

Steps To Take While You Wait

The waiting period between the swab and the result is a good time to check a few boxes on your third-trimester prep list. These steps keep the information moving and prevent last-minute surprises when labor starts.

1. Ask your provider about the result timeline. Some offices call only for positive results and auto-post negatives to the portal. Knowing this avoids unnecessary worry if your phone stays quiet.
2. Note the exact swab date. If 72 hours have passed and you still have not heard anything, a brief call to the office or lab is a reasonable follow-up. The result may have been filed without notification.
3. Discuss penicillin allergy in advance. If you have a known allergy, flag it for your provider now so the lab can run susceptibility testing ahead of time rather than rushing during labor.
4. Write down the result for your birth plan. If you test positive, include a note that IV antibiotics are recommended once labor begins. It is one less thing to explain when you are focused on contractions.

Having a clear timeline and a simple follow-up plan makes the wait feel less open-ended. Most of the time the result arrives right on schedule, and you can cross GBS off your third-trimester list entirely.

What The Results Mean For Your Birth Plan

A positive GBS result changes the labor room setup only slightly. You will receive IV antibiotics, typically every four hours, until delivery. Penicillin is the standard choice unless an allergy or another condition points to an alternative. The antibiotics lower the chance of early-onset GBS disease in newborns.

A negative result means you do not need antibiotics for GBS prevention specifically. Providers can skip the IV line for that purpose, though many people receive IV fluids during labor anyway through a heparin lock. The swab result is recorded in your chart and travels with you to the delivery unit.

MedlinePlus notes that results are typically ready within a 24 to 48 hours window after the lab receives the sample. If you test positive, there is no need to worry about having GBS itself — it is a common colonization, not an illness. The whole point of the late-pregnancy screen is to build a simple medical layer that protects the baby during the birth process.

The Bottom Line

GBS test results almost always land within 24 to 48 hours, and the swab is a quick, standard part of late-pregnancy care. A positive result is not a diagnosis of illness — it is simply a signal to add antibiotics during labor, a step that is routine and well-studied.

Your obstetrician or midwife can walk you through your specific result, confirm whether your allergy history affects the antibiotic choice, and help you fold the plan into your birth preferences without it feeling like one more complication.