What is the benefit of screening for B streptococcus bacteria during pregnancy?

Photo of a pregnant woman with her daughter (PantherMedia / Leo Lintang)

Pregnant women who have a greater risk of infecting their baby with group B streptococcus bacteria are given an antibiotic during labor. This is done to protect the baby from infection. It’s not clear whether it makes sense to routinely screen for group B streptococcus bacteria in all pregnant women.

Routine screening tests are carried out during pregnancy to see whether the baby is developing normally and the mother is healthy. These tests include ultrasound scans and blood tests, as well as urine tests. In Germany, special guidelines (“Mutterschafts-Richtlinien”) specify what is to be tested in pregnancy, and what sorts of tests are used.

If doctors think that a pregnant woman carries group B streptococcus bacteria in her body, she is given an antibiotic during labor. This is done to prevent the baby from being infected and becoming very ill.

Group B streptococcus bacteria: Harmless for adults, but dangerous for babies

Group B streptococcus bacteria may live in the human body, especially in the bowel and genital area.

In healthy adults, group B streptococcus bacteria usually don't cause any problems. That’s different in newborn babies: Then the bacteria can lead to blood poisoning (septicemia) or even death. Group B streptococcus bacteria can also cause various infectious diseases in babies, such as meningitis or pneumonia, and result in permanent disability.

About 1,800 out of 10,000 pregnant women in Germany carry group B streptococcus in their body. The bacteria can be spread to the baby during a natural (vaginal) birth. In Germany, about 3 out of 10,000 newborns develop a group B streptococcus bacteria infection. Only very rarely do they die of it.

Group B streptococcus test in pregnancy

The group B streptococcus test can be done to find out whether a pregnant woman has these bacteria in her body. The test is typically offered towards the end of pregnancy, between 34 and 36 completed weeks of pregnancy.

In Germany, the costs of this test are covered by all statutory health insurers if the doctor or midwife thinks that the pregnant woman has group B streptococcus bacteria in her body or if there's a risk of premature birth. If a woman would like to have the test done even though the doctor doesn't think she has these bacteria in her body, she has to pay for it herself. Then the test is offered as an individual health care service (in German: individuelle Gesundheitsleistung, or IGeL for short). Some statutory health insurers cover the costs of the test for all pregnant women, though.

The test usually involves taking two smear samples: one from the vagina and one from the anal area. These cell samples are typically sent to a laboratory and the results are usually available within a week. If the test finds group B streptococcus bacteria in the woman's cells, it is recorded in her maternity-related medical records (in German: Mutterpass).

When is the baby at greater risk of infection?

It’s assumed that the baby's risk of infection is higher if the pregnant woman has at least one of the following risk factors:

  • Group B streptococcus bacteria are found in a urine sample.
  • Group B streptococcus bacteria are found in the vaginal or anal area (group B streptococcus test).
  • There is a risk of premature birth before 38 completed weeks of pregnancy.
  • The woman develops fever during birth, i.e. a body temperature of 38°C or higher.
  • At least 18 hours pass between the mother's water breaking and the birth.
  • The woman has already given birth to another child that became infected with group B streptococcus bacteria during the birth.

If the baby has a higher risk of infection, then the woman is given an antibiotic during the birth to protect the child from infection. This antibiotic is either injected or given as an infusion (IV drip).

Group B streptococcus bacteria screening during pregnancy

In some countries, all women are routinely screened for group B streptococcus bacteria towards the end of their pregnancy. This routine test is known as group B streptococcus screening. The current guidelines issued by the German Society of Gynecology and Obstetrics also recommends this type of screening.

If the test shows evidence of group B streptococcus bacteria in the sample taken from a pregnant woman, she is usually given an antibiotic during birth. If the test doesn't find any streptococcus bacteria, no antibiotic is needed. There are two exceptions in which an antibiotic will still be given even if the test doesn’t detect any group B streptococcus bacteria:

  1. The woman has already given birth to another child that became infected with group B streptococcus bacteria during the birth.
  2. Group B streptococcus bacteria were found in the pregnant woman’s urine.

Research on screening for group B streptococcus bacteria

The Institute for Quality and Efficiency in Health Care (IQWiG, Germany) looked into the advantages or disadvantages of routinely screening for group B streptococcus bacteria in all pregnant women. The researchers at IQWiG wanted to compare group B streptococcus screening with the approach of giving an antibiotic during birth if the woman has specific risk factors.

But they didn't find any good-quality studies on the advantages or disadvantages of the screening test for mothers and their babies. So it remains unclear whether babies can be better protected from a group B streptococcus infection by a screening test or by the approach based on risk factors. It is also not clear whether the screening test helps women to avoid taking antibiotics although they don’t need to.