Group B Strep Testing In Pregnancy

What is Group B Strep Test?

Group B streptococcus also known as Group B strep is a commonly found species of bacteria in the gut and genital tract of healthy humans. These bacteria are not harmful in adults but in pregnant women and in newborns the bacteria can lead to serious and even life-threatening medical conditions. A gynecologist may recommend that a pregnant woman has group B strep tests done by the third trimester. A vaginal and/or rectal swab is sent to the laboratory to test for presence of group B strep. A negative test result does not require any treatment but a positive test result requires antibiotic administration during labor. The test may be repeated on consecutive pregnancies as the results can change from time to time.

Reasons For Testing

The group B strep test is recommended for pregnant women in order to identify whether they harbor the bacteria in their body. These bacteria can increase the risk of spreading the infection to their newborn babies. Group B strep usually does not cause any significant complications in healthy adults. However, during pregnancy certain complications may occur such as a urinary tract infection or even an infection f the placenta and the amniotic fluid (chorioamniotitis).

Sometimes the bacteria may spread to the blood tream leading to bacteremia and in severe cases the bacteria can start multiplying in the circulation resulting into life threatening infection (septicemia). On rare occasion the bacteria may infect the inner lining of the uterus resulting in endometritis especially immediately after delivery. Presence of these bacteria also increases the risk of infection at the incision site after caesarean section.

Infection of the newborn by group B streptococcus is the main concern. Bacterial infection can occur as the baby during passes through the birth canal during contact with the vaginal fluid.

Group B Strep Dangers In Newborns

Not all the babies who come in contact with group B strep will acquire an infection. In fact only a minority of newborns will become infected. Nevertheless the risks associated with this type of infection in newborns makes it important to test for in high risk pregnant woman. In the newborn, the infection may lead to serious complications immediately after birth or within the first few days, weeks or even months of life

Life threatening complications that occur in the baby include infection of the lungs (pneumonia) and the protective covering around the brain and the spinal cord (meningitis) although a number of other sites may be infected. The other two serious complications similar to infection in the pregnant mother include bacteremia and septicemia.

Who Should Be Tested?

Pregnant women who had a history of spreading group B strep infection to previously delivered babies or a history of urinary tract infection during the current pregnancy have a higher chance of spreading the infection to the baby during vaginal delivery. Testing in these women are therefore important.

Antibiotic therapy should be commenced during labor since earlier antibiotic administration may still lead to a recurrence of the bacteria. Antibiotic treatment is not necessary if caesarean section delivery has been planned and the amniotic fluid filled membrane is intact around the baby. Although sometimes labor can start following rupture of the amniotic sac before scheduled caesarean section delivery.

Testing Procedure

Group B strep test is usually done between 35 and 37 weeks of pregnancy. The consulting doctor will inquire about group B strep status of the person, if known and also whether the mother had previously delivered a baby who suffered from strep B infection. The testing is usually done at the doctor’s office. The woman is asked lie on her back while the doctor collects vaginal and rectal secretions using a cotton swab. Sometimes the pregnant mother herself collects the sample after being properly instructed. It then takes several days before the results will be available.

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