Group B Streptococcus (GBS) is a common bacterium that lives naturally in the gastrointestinal and genitourinary tracts of many healthy people. For pregnant individuals, a GBS swab is a screening test to determine if the bacteria colonizes the lower vagina and rectal area. The main purpose of this screening is to prevent the transmission of GBS to the newborn during a vaginal birth, which could otherwise lead to serious, life-threatening infections such as sepsis or meningitis in the baby. The procedure is typically recommended late in the third trimester of pregnancy, usually between 36 and 37 weeks gestation, as this timing best predicts colonization status at the time of delivery.
Preparing for the GBS Swab
Minimal preparation is generally required for the GBS swab, but following specific guidelines from your healthcare provider ensures the most accurate result. You should generally not douche or use vaginal creams, gels, or suppositories for at least 48 hours before the collection. These products can interfere with the bacterial growth in the lab culture, potentially leading to a false-negative result.
In most cases, the healthcare provider’s office will provide the sterile collection kit and instructions. The swab may be collected by a nurse or midwife, or you may be given the option to self-collect the sample in a private area. If self-collecting, ensure the swab remains sterile and do not touch the cotton tip with your fingers or any other surface before or during collection.
Step-by-Step GBS Swab Procedure
The GBS swab procedure involves collecting a sample from two distinct anatomical areas using a single swab: the lower vagina and the rectum. Collecting from both sites maximizes the detection rate, as the bacteria may be present in one area but not the other. This dual-site collection is based on current guidelines to ensure the most accurate screening for colonization.
To begin the collection, remove the sterile swab from its packaging, handling only the plastic end. Finding a comfortable position, such as sitting on a toilet with one leg raised or standing, makes the process easier. Gently insert the cotton tip approximately 2 centimeters into the lower vagina, rotating it gently for 10 to 15 seconds against the vaginal walls.
Immediately after swabbing the vagina, use the same swab for the second site. Insert the swab approximately 1 centimeter into the anus, just past the anal sphincter, and rotate it slightly.
After the collection from both sites is complete, the swab is immediately placed into the provided sterile transport tube, which often contains a transport medium. The cap must be closed tightly to prevent contamination and maintain the sample’s integrity for transport to the laboratory. The transport tube is then labeled with your identifying information and the date and time of collection before being handed over to the healthcare staff.
Interpreting Results and Treatment Protocols
A GBS screening result will be reported as either positive or negative. A positive result simply means the bacteria is present, or “colonizing,” at the time of the test. GBS colonization in the mother rarely causes illness for her, and the test result does not mean an active infection is present. A negative result means the bacteria was not detected, suggesting a low likelihood of colonization at the time of delivery.
For an individual who tests GBS-positive, the standard medical protocol is to administer prophylactic intravenous (IV) antibiotics during labor. This intrapartum antibiotic prophylaxis (IAP) is highly effective, reducing the risk of the baby developing an early-onset GBS infection. The antibiotics, typically penicillin or ampicillin, are most effective when given for at least four hours before the baby is born.
Treatment is not recommended before labor begins because GBS bacteria can quickly return, making the antibiotics ineffective at the time of birth. However, there are scenarios where IAP is recommended even without a positive swab result, such as if GBS was detected in a urine sample at any point during the pregnancy. A previous baby with a GBS infection or the onset of preterm labor also prompts the recommendation for IAP.
If you test positive, notify your care team immediately upon arriving at the hospital in labor to ensure the antibiotic protocol is started promptly. Even with IAP, the newborn will be closely monitored for signs of infection for a period after birth.