Group B Strep Test

image001It is not unusual for some healthy women to harbor Group B streptococcus bacteria in their rectum and vagina. These microorganisms do not usually cause disease when few in number, but when they grow in number and colonize these areas, bacterial infection can become severe.

A woman who is pregnant and tests positive for Group B strep or GBS may pass the bacteria to her baby during childbirth. GBS affects one out of 2,000 newborns in the US, although not all babies born to GBS-positive mothers become ill. Doctors may routinely test pregnant women for GBS during their prenatal visits even if this type of infection is rare because severe outcomes can occur.

Why Is a Group B Strep Test Needed?

For the Mother

Although harmless to most adults, pregnant women may experience health problems associated with these bacteria, which can cause:

  • UTI or urinary tract infection
  • Chorioamnionitis (infection of the amniotic fluid and placenta)
  • Bacteremia (infection of the blood)
  • Sepsis (severe, widespread blood infection)

After normal delivery, GBS can also lead to infection of the inner lining (endometrium) of the uterus. For mothers who deliver by C-section, wound infection risk is increased.

For the Baby

A prenatal test for group B strep may also be done to protect a baby from exposure to the bacteria during normal childbirth. Although not all babies develop infection, affected babies could suffer from severe complications immediately or even sometime after birth. These life-threatening complications include:

  • Pneumonia (lung infection and inflammation)
  • Meningitis (infection of the membranes covering the brain)
  • Bacteremia
  • Sepsis

Women who test positive for GBS are usually given antibiotics during childbirth to eliminate bacteria in their birth canals. However, there is no benefit from taking these medications before labor since strep bacteria can rapidly grow back.

Risk Factors and How to Reduce Risks 

The risk of transmitting the bacteria to your baby is greater if you previously had a baby who got infected with group B strep after birth. Your baby is also in danger of contracting the infection if you currently have a UTI caused by these bacteria. You will receive antibiotic treatment during labor if you have these histories even without being tested.

For women who are going to give birth by C-section, antibiotics are not necessary if labor has not begun and the water bag is still intact. However, testing will be done because labor can ensue before the planned procedure.

How Is a Group B Strep Test Done?

When: The screening test is usually done during the prenatal visit at 35-37 weeks as recommended by most health experts of the CDC, AAP, and ACOG. Rapid tests, which are done in some hospitals just before delivery, are less sensitive and may not be able to detect the bacteria.

How: A GBS test is a painless test that involves taking samples of fluids from your vagina and rectum using swabs. These swabs are sent to the lab where cultures of microorganism are grown. The test is positive if GBS bacteria are present in the culture after two or three days. Ask your doctor for the results during your next visit.

What If I Tested Positive in a Group B Strep Test?

Testing positive for group B streptococcus does not always mean that you are infected or that your baby will be ill. It just means that you are carrying the bacteria in your body, and only one in 200 babies may develop a disease if the mother is not given antibiotics.

There are symptoms, however, that indicate you are more likely to deliver a baby with GBS, such as:

  • If labor commences or your membranes rupture before 37 weeks
  • If your membranes rupture at least 18 hours before delivery
  • If you develop a fever during your labor
  • If you develop UTI from GBS during pregnancy
  • If you previously had a baby with the disease

Your physician will treat you with antibiotics to prevent infection and protect your baby. The likelihood of delivering a newborn with GBS is lower (one in 4000) if antibiotics are used in women who get a positive test. Furthermore, treatment also decreases your risk of developing uterine infection during or after childbirth.

Doctors usually start antibiotic treatment about 4 hours before delivery, but in women who undergo rapid labor, starting treatment even a few hours before the baby comes out reduces risk of infection. Do not worry about your baby getting sick, especially if she is full-term and you do not have symptoms, because the risk is not great.

How to Prevent My Baby from Getting Group B Strep Infection

Mothers who test positive and are at high risk for GBS infection will be given IV antibiotics to reduce their babies' chances of developing the infection after birth. Some women are carriers of group B strep, which means that the bacteria live in their gastrointestinal tract without causing symptoms. They may or may not test positive all the time, thus it is important to screen pregnant women for GBS at 35-37 weeks of pregnancy. Antibiotics are not given before the onset of labor since the bacteria can thrive again after treatment.

The decision to have antibiotic treatment depends on you, if you have a low risk of having GBS. Some homeopathic physicians recommend taking herbal remedies to prevent infection a few weeks before delivery.

Early-Onset GBS Infection and Late-Onset GBS Infection 

GBS infection in babies may have an early onset or late onset.

Early onset signs and symptoms occur within hours after delivery, and include:

  • Breathing problems
  • Unstable heart rate and blood pressure
  • Gastrointestinal problems
  • Kidney problems

Common complications include pneumonia, meningitis, and sepsis. The treatment for newborns with GBS infection involves the use of intravenous antibiotics.

Late-onset signs and symptoms occur within a week or months after delivery, and include Meningitis (most common). Late-onset infection is not common and it could be due to the baby's delivery, or from having contact with someone who is infected. Unfortunately, antibiotic treatment during labor cannot prevent it. Half of the newborns who get a late-onset GBS infection are delivered by GBS carriers, while others are infected through unknown mechanisms. Prevention of the disease is therefore difficult.

Research on developing a vaccine that can prevent maternal and neonatal GBS infection is underway. More studies on testing and treatment for the disease are also being done.

Watch a video to learn more about Group B Strep Test (GBS):