The group B strep test is a test that is done between 35 and 37 weeks of pregnancy to look for the presence of Streptococcus agalactiae, a type of bacteria that can be passed from mother to baby during birth, causing newborn complications like respiratory problems, cardiac issues, and kidney problems.
This exam involves using a swab to collect a sample from the vagina and the anus, as these are the areas where the bacteria normally lives. Your OBGYN or midwife can collect the sample, or you may be given the option to collect the sample yourself if you prefer. The sample is then sent to the lab to be analyzed.
Group B Streptococcus, or group B strep (GBS), is a bacterium that normally lives in the gut, urinary tract, and vagina without causing any symptoms. In some situations, however, an overgrowth of GBS in the vagina has the potential to cause complications during pregnancy and birth.
Indications for testing
The group B strep test is used to identify the presence of group B strep (GBS), which may be found at any point in pregnancy as it is a type of bacteria that is found naturally in the urinary tract. Being a "carrier" of GBS does not mean you have an infection.
In the majority of cases, GBS does not cause any signs or symptoms. In some cases, GBS may cause an infection in pregnancy such as a UTI (urinary tract infection), but this is uncommon.
GBS that is not identified and treated may increase the risk for:
- Miscarriage;
- Premature labor and birth;
- Lung, heart, and kidney problems in the newborn;
- Death of the newborn (in the most serious cases)
It is therefore important to have the group B strep test done as directed by your OBGYN or midwife so that GBS can be identified and treated as necessary.
Also recommended: Streptococcus agalactiae: Symptoms, Diagnosis & Treatment tuasaude.com/en/streptococcus-agalactiaeHow the test is performed
The group B strep test is simple and easy to do, with no special preparation required. Your OBGYN or midwife will have you lie back on the exam table with your feet together (or on foots rests) and your knees apart and will use a swab to collect a sample from the vagina and the anus. Tell your provider if you are more comfortable collecting the sample yourself.
After the sample is collected, the swab is sent to the lab for analysis. Results usually take about 24 to 48 hours. If the result is positive, your provider will confirm that you do not have any symptoms of infection requiring immediate treatment. If you are asymptomatic, IV antibiotics will be given in labor (ideally at least 4 hours prior to delivery) to prevent GBS infection in the newborn.
Treatment in the days or weeks prior to the birth is not indicated in people who are asymptomatic for infection, as GBS is found naturally in the body. Similarly, IV antibiotics should still be given during labor even if GBS was treated earlier in pregnancy, as there is the potential that the bacteria could grow back, leading to risks for the newborn baby.
Risk factors
Some risk factors for passing group B strep to the newborn include:
- Having tested positive for GBS in prior pregnancies;
- Being diagnosed with a group B strep UTI during pregnancy;
- Preterm birth prior to 37 weeks gestation;
- Fever during labor;
- Prolonged rupture of membranes (meaning your water has been broken for more than 18 hours);
- History of a previous baby infected with GBS or another type of infection.
If GBS is identified during pregnancy, you will receive IV antibiotics during labor to prevent complications. If you have not had a GBS test done, the OBGYN or midwife will determine whether you need prophylactic (preventive) antibiotics in labor.