Group B Strep in Pregnancy

Carrying GBS is not an infection

The RCOG describes group B Streptococcus as "a common bacterium (bug) which is carried in the vagina and rectum of 2-4 in 10 women (20-40%) in the UK", adds that "GBS is not a sexually transmitted disease and most women carrying GBS will have no symptoms", and states that "carrying GBS is not harmful to you but it can affect your baby around the time of birth".

Green-top Guideline No. 36 gives the same colonisation figure - "GBS is present in the bowel flora of 20-40% of adults" - and calls those people carriers rather than patients. Nothing about your health changes because of a positive swab. What changes is the plan for labour.

Why the UK does not screen everyone

This is the part that generates the most anger and the most confusion, so it is worth stating both positions accurately rather than picking one.

The NHS explains the UK position: "Routine testing is not currently recommended and tests are rarely done on the NHS. This is because group B strep is very common and testing cannot predict whether a baby will get an infection." Carriage comes and goes, so a swab weeks before birth does not reliably describe the situation on the day.

ACOG takes the opposite approach in the United States: it "now recommends performing universal GBS screening between 36 0/7 and 37 6/7 weeks of gestation", and "all women whose vaginal-rectal cultures at 36 0/7-37 6/7 weeks of gestation are positive for GBS should receive appropriate intrapartum antibiotic prophylaxis unless a prelabor cesarean birth is performed in the setting of intact membranes".

Both are defensible readings of the same evidence. If you are in the UK and want a test, you can pay for one privately; the NHS links to Group B Strep Support for information on where.

The numbers, without rounding them into fog

Green-top Guideline No. 36 reports that "in 2015, the incidence of EOGBS in the UK and Ireland was 0.57/1000 births (517 cases), a significant increase from the previous surveillance undertaken in 2000 where an incidence of 0.48/1000 was recorded".

The RCOG patient information puts the same risk in everyday terms: "Around 1 in every 1750 newborn babies in the UK and Ireland is diagnosed with early-onset GBS infection." Of the babies who do develop it, "1 in 19 (5.2%) will die and, of the survivors, 1 in 14 (7.4%) will have a long-term disability".

The RCOG then translates that into a monthly picture, which is the clearest framing available: on average in the UK each month, 43 babies develop early-onset GBS infection, 38 make a full recovery, 3 survive with long-term physical or mental disabilities, and 2 die.

ACOG adds the transmission figure: "Approximately 50% of women who are colonized with GBS will transmit the bacteria to their newborns", and "in the absence of intrapartum antibiotic prophylaxis, 1-2% of those newborns will develop GBS EOD."

What changes if GBS is found

You are offered antibiotics through a drip once labour starts. The RCOG quantifies the benefit: "These antibiotics reduce the risk of your baby developing a GBS infection in their first week of life from around 1 in 400 to 1 in 4000."

Two consequences follow that most people are not told at the time. First, place of birth becomes a practical question: "If you choose to have antibiotics, they will be given through a drip and it may not always be possible to arrange this at home or in some midwifery-led units." Second, timing matters: "As soon as you go into labour or your waters break, contact your healthcare professional as it is important that you have antibiotics as soon as possible."

ACOG notes that while four or more hours of antibiotics before birth is most effective, "2 hours of antibiotic exposure has been shown to reduce GBS vaginal colony counts and decrease the frequency of a clinical neonatal sepsis diagnosis", and that obstetric interventions should not be delayed solely to complete four hours.

What does not change

Antibiotics before labour are not offered and are not useful: "If you are found to carry GBS in your vagina or rectum, treating you with antibiotics before your labour begins does not reduce the chance of your baby developing GBS infection."

A planned caesarean with intact membranes does not need GBS-specific antibiotics either, although everyone having a caesarean is offered antibiotics for other reasons.

There is one exception to the "wait for labour" rule. If GBS is found in your urine, that is a urinary tract infection: "A urine infection caused by GBS should be treated with antibiotic tablets straight away and you should also be offered antibiotics through a drip during labour."

Waters breaking, and preterm labour

If your waters break after 37 weeks and you are known to carry GBS, "you will be offered induction of labour straight away. This is to reduce the time that your baby is exposed to GBS before birth." You are offered the drip as well.

If labour starts before 37 weeks, antibiotics are recommended "even if you are not known to carry GBS". The same applies if you develop signs of infection in labour at any gestation.

The RCOG lists the features that increase your baby's risk: preterm birth (the earlier, the greater the risk), a previous baby affected by GBS, a high temperature or other signs of infection in labour, any positive urine or swab test for GBS in this pregnancy, and waters breaking more than 24 hours before birth.

Previous pregnancies

These two situations are treated differently and are often conflated.

If a previous baby had GBS infection, "you should be offered antibiotics during labour in all following pregnancies". No test needed.

If GBS was found in a previous pregnancy but your baby was unaffected, "there is a 1 in 2 (50%) chance that you will be carrying it again in this pregnancy". You can have a specific enriched culture medium (ECM) swab at 35 to 37 weeks to inform the decision.

After the birth

Your baby may be monitored in hospital for up to 12 hours. The NHS lists the signs to act on, and they can appear up to three months after birth: being floppy or unresponsive, grunting or working hard to breathe, very fast or slow breathing, an unusually high or low temperature, changes in skin colour or blotchy skin, poor feeding or vomiting milk up, and an unusually fast or slow heart rate. The NHS instruction for those signs is to call 999 or go to A and E.