Group B strep (GBS) in pregnancy: the swab, antibiotics in labour and your baby
In this article
Group B strep (GBS, short for group B streptococcus) is a common bacterium that can live in the vagina and rectum, usually without any symptoms. KKH says about one in five women carry it, and it is not a sexually transmitted infection. It rarely harms you, but it can pass to your baby around birth, so KKH offers a swab test between 35 and 37 weeks of pregnancy.
| Carriers | About 1 in 5 women, KKH says |
|---|---|
| Test | Vaginal swab at 35 to 37 weeks, for a planned vaginal birth |
| If positive | Antibiotics through a drip in labour, every 4 hours until birth |
| Babies unaffected | 98 to 99% of babies exposed to GBS |
| Watch period | Most sick babies show signs within 12 to 24 hours |
The GBS swab at 35 to 37 weeks
At KKH, every pregnant woman planned for a vaginal delivery is offered a GBS swab test between 35 and 37 weeks. GBS can also turn up in a urine test. Use our due date calculator to see when that window falls for you, and ask your gynae at the 34 or 35 week visit if the swab has not been mentioned.
Practice differs abroad. The NHS does not routinely test, because GBS is very common and a positive test cannot predict which babies will get ill. Singapore hospitals such as KKH test so that carriers can be treated in labour.
Planning a C-section? KKH says you do not need antibiotics for GBS unless labour has started or your water bag has broken. You will be offered antibiotics at the operation anyway, to cut the risk of other infections.
If your swab is positive
KKH says you will be offered antibiotics through a drip as soon as labour starts or your water bag breaks, repeated every 4 hours until your baby is born. Penicillin is the usual choice, with an alternative if you are allergic.
Timing matters most when your waters go first. If they break after 37 weeks and you are known to carry GBS, KKH offers induction of labour straight away to shorten the time your baby is exposed. So if you are GBS positive and think your waters have broken, go to the hospital rather than waiting at home. You can breastfeed as normal; KKH says it does not raise the risk of infection.
Which babies are at higher risk
KKH says 98 to 99% of babies exposed to GBS have no ill effects. The 1 to 2% who develop a serious infection can become very ill. The risk is higher for:
- babies born before 37 weeks (premature birth)
- a baby whose older sibling had GBS infection
- a mother with a fever in labour
- waters broken more than 18 hours before the birth
KKH says antibiotics in labour lower the risk of early-onset infection, the kind that shows in the first week. They do not prevent late-onset infection, which can appear up to three months after birth. Our GBS in pregnancy guide covers the hospital steps in more detail.
Signs of GBS infection in your newborn
KKH says most infected babies show symptoms within 12 to 24 hours of birth, while you are still in the ward and being watched. At home, it asks parents to get medical help immediately for any of these:
- breathlessness or turning blue
- repeated vomiting
- fever, or a temperature below the normal 36.5 to 37.5C
- poor feeding or refusing milk
- fits, stiffening or jerking movements
- unusual sleepiness, irritability or non-stop crying
The NHS gives a similar list and says to go to A&E if your baby has these signs. For a raised temperature on its own, see fever in a newborn.
Frequently asked questions
What does GBS positive mean in pregnancy?
It means the swab found group B strep in your vagina or rectum. It is common, about 1 in 5 women, and usually harmless to you. You will be offered antibiotics in labour to protect your baby.
Is GBS a sexually transmitted infection?
No. KKH says GBS is not a sexually transmitted disease, and most women who carry it have no symptoms.
Can I breastfeed if I carry GBS?
Yes. KKH says breastfeeding has not been shown to increase the risk of GBS infection in your baby.
Do I need antibiotics for a planned C-section?
Not for GBS, unless labour has started or your water bag has broken first, KKH says. You will still get antibiotics at the operation to lower the risk of other infections linked to surgery.
Related terms
- Rupture of Membranes (Water Breaking): When the bag of fluid around your baby breaks and leaks out through the vagina, as a gush or a trickle.
- Induction of Labour: Starting labour with medical help, such as a pessary, balloon or drip, instead of waiting for it to begin.
- Preterm (Premature) Birth: A baby born alive before 37 completed weeks of pregnancy. In Singapore, about 8.5% of babies arrive this early.
- Fever in a Newborn: A raised temperature in a baby under 3 months, which Singapore hospitals treat as a reason to come in straight away.
- C-section (Caesarean Section): An operation to deliver your baby through a cut in your tummy and womb, planned ahead or done in labour.
- Neonate (Newborn): The medical word for a newborn baby in the first 28 days of life.
