Why it's done

Although group B strep is usually harmless in adults, it can cause complications during pregnancy and serious illness in newborns. The group B strep test is done during pregnancy to identify women who carry the bacterium.

Rarely, however, group B strep can cause health problems during pregnancy, including:

• Urinary tract infection
• Infection of the placenta and amniotic fluid
• Pneumonia
• Bacteria in the blood
• Life-threatening infection in the blood

Group B strep may lead to inflammation and infection of the membrane lining the uterus after delivery, though this is rare. Group B strep also increases the risk of wound infection after a C-section.

The biggest concern is that group B strep can spread to the baby during a vaginal delivery. While only a few babies exposed to group B strep develop an infection, those do develop an infection can develop life-threatening complications. These complications often happen shortly after birth, but sometimes don't develop until days or even months later.

Complications for the baby could include:

• Inflammation of the lungs (pneumonia)
• Inflammation of the membranes and fluid surrounding the brain and spinal cord (meningitis)
• Bacteria in the blood (bacteremia)
• Life-threatening infection in the blood (sepsis)

If you have group B strep, you'll likely be given IV antibiotics during labor — at least four hours before birth. The antibiotics will destroy bacteria in the birth canal and reduce your baby's risk of developing an infection.

Taking antibiotics by mouth or any other route is ineffective. Also, taking antibiotics before labor doesn't help since the bacteria can grow back quickly.

If you previously gave birth to a baby who had a group B strep infection or you had a urinary tract infection caused by group B strep during your current pregnancy, you're at higher risk of spreading group B strep to your baby. As a result, you'll automatically be treated with antibiotics during labor.

Antibiotics aren't necessary if you're having a planned C-section, as long as labor hasn't begun and the amniotic sac — the fluid-filled membrane that surrounds and cushions your baby during pregnancy — is intact. Testing is still important, however, since labor could begin naturally before the scheduled C-section.