Group B Strep in Pregnancy: The 36-Week Swab, Labor Antibiotics and the UK

What is group B strep in pregnancy?

Group B strep (GBS) is a common bacterium that lives in the vagina and rectum of many healthy women and can pass to the baby during labor. ACOG says about 1 in 4 pregnant women carry it, and the RCOG puts the UK figure at 2 to 4 in 10. It usually causes no symptoms, it is not a sexually transmitted infection, and ACOG notes it is different from group A strep, which causes strep throat.

The RCOG says carrying GBS is not harmful to you, though it can affect your baby around the time of birth. ACOG's committee opinion says about half of women who carry GBS pass it to their newborns, and without antibiotics in labor, 1 to 2% of those newborns develop early-onset GBS disease. The US and the UK handle this differently:

When is the group B strep test done?

In the US, the group B strep test is done between 36 weeks 0 days and 37 weeks 6 days of every pregnancy, as ACOG's committee opinion recommends. ACOG's patient FAQ, which gives 36 to 38 weeks, describes the test as a swab of the vagina and rectum.

The CDC says GBS comes and goes naturally in the body, which is why testing is done late in pregnancy, close to the birth. The CDC also says screening should happen even if a cesarean birth is planned, and ACOG explains that labor may start before the planned date. If you are allergic to penicillin, ACOG says to tell your care team before you are tested; other antibiotics can be used.

Why doesn't the UK test everyone for group B strep?

The UK does not test every pregnant woman because the UK National Screening Committee does not recommend it. The RCOG gives these reasons: most carriers' babies are born safely, late testing cannot accurately predict which babies will become ill, a negative swab is no guarantee, many severely affected babies are born preterm before the 35 to 37 week testing time, and treating every carrier would give many women antibiotics they do not need. The NHS says routine testing is rarely done on the NHS and that you can pay for a private test.

If GBS was found in a past pregnancy and your baby was not affected, the RCOG says there is a 1 in 2 chance you carry it again, and you can have a special swab (the ECM test) at 35 to 37 weeks. A positive result raises the baby's risk of early-onset infection to around 1 in 400, and you will be offered antibiotics; a negative one puts it at about 1 in 5,000, and you may choose not to have them.

What happens if you test positive for group B strep?

If you test positive, you will be offered antibiotics through an IV once labor starts, usually penicillin, to protect your baby. ACOG says the best time for treatment is during labor, and the RCOG says antibiotics taken before labor do not lower the baby's chance of infection. The RCOG says the antibiotics start as soon as possible after labor begins or your waters break, are repeated usually every 4 hours until the birth, and reduce the risk of GBS infection in the baby's first week from around 1 in 400 to 1 in 4,000. ACOG's committee opinion says 4 or more hours of antibiotics before birth works best, that 2 hours still helps, and that needed obstetric care should not be delayed only to reach 4 hours.

The RCOG adds that an IV may not be possible at home or in some midwife-led units, so plan where you give birth, and that if your waters break after 37 weeks and you carry GBS, you will be offered induction straight away. With a planned cesarean before labor and with your waters intact, ACOG says you do not need GBS antibiotics during the cesarean. ACOG also says antibiotics in labor do not prevent late-onset GBS disease, which can start after the first week.

When are antibiotics given without a test result?

ACOG says antibiotics may be given in labor without a GBS test if:

• you had a previous baby with GBS disease
• GBS was found in your urine at any point in this pregnancy
• your GBS status is unknown and you have a fever in labor
• your status is unknown and labor starts before 37 weeks
• your status is unknown and it has been 18 hours or more since your water broke
• your status is unknown but you tested positive in a past pregnancy

In the UK, the RCOG offers antibiotics in labor, even if you are not known to carry GBS, when labor starts before 37 weeks or you show signs of infection, and in every pregnancy after a baby who had GBS infection. It counts waters breaking more than 24 hours before the birth as a risk factor.

How can group B strep affect a newborn?

Group B strep can cause sepsis, pneumonia and meningitis in a newborn, most often in the first week. ACOG says early-onset disease usually starts within 12 to 48 hours of birth or up to 7 days, and the RCOG says most affected babies become unwell within 12 to 24 hours. Late-onset disease can start from a week to a few months after birth, according to ACOG, and the RCOG and NHS say up to 3 months.

The RCOG says around 1 in 1,750 newborns in the UK and Ireland is diagnosed with early-onset GBS infection, and most recover fully with prompt treatment. Of those babies, 1 in 19 die and 1 in 14 survivors have a long-term disability. Breastfeeding is safe, the RCOG adds, and has not been shown to raise the risk of GBS infection.

When should you call your doctor or midwife?

Call your doctor or midwife, or the hospital, right away if:

• labor starts or your waters break and you carry GBS or had a baby with GBS before; the RCOG says antibiotics should start as soon as possible
• you have a high temperature or other signs of infection in labor
• you have signs of preterm labor before 37 weeks

Watch your baby for these signs for up to 3 months (RCOG, NHS):

• grunting, noisy breathing, moaning, working hard to breathe, or not breathing at all
• being very sleepy, floppy or not responding normally
• crying that cannot be soothed
• not feeding well or vomiting milk up
• a high or low temperature, or skin that feels too hot or cold
• changes in skin color, or blotchy skin
• an unusually fast or slow heart rate or breathing

ACOG says to contact your baby's health care professional right away for signs such as lack of energy, irritability, poor feeding or a high fever. The NHS says to call 999 or go to A&E, and not to drive yourself.