Group B strep in pregnancy: the 35 to 37 week swab and antibiotics in labour in Singapore

Group B strep (GBS) is a common bacterium that about one in five women carry in the vagina or rectum, usually with no symptoms. It isn't a sexually transmitted infection and it rarely harms you, but it can occasionally cause a serious infection in a newborn. At KKH, every pregnant woman planned for a vaginal birth is offered a swab test for GBS between 35 and 37 weeks. If it's positive, or a previous baby had GBS infection, you're offered antibiotics through a drip as soon as labour starts or your waters break, repeated every four hours until birth, with penicillin as the first choice. This guide covers the swab, the labour plan, caesareans and breastfeeding, plus the warning signs to watch for in your baby.

What group B strep is

KKH describes GBS as a type of bacterium that can live in the vagina and rectum. About one in five women carry it, and most never know. Carrying it isn't a sign of poor hygiene and isn't caught through sex.

The concern is your baby. Babies can be exposed to GBS during labour or around birth. KKH says 98 to 99% of exposed babies have no ill effects, but 1 to 2% may develop serious infections, which can be fatal or leave long-term disabilities. Antibiotics in labour lower that risk, which is why Singapore hospitals test for it.

The GBS swab at 35 to 37 weeks

KKH offers the screening swab to every pregnant woman planned for a vaginal birth between 35 and 37 weeks. Its laboratory guide recommends universal screening of all pregnant women in this window. The test takes a few seconds:

• A low vaginal swab or a swab of the anus and rectum, taken at your antenatal visit.
• KKH's lab catalogue gives one to two days for results.
• GBS can also show up in a urine test during pregnancy.

If you see a private gynae or deliver at another hospital, ask at your 34 or 35 week visit when your swab is due. Our 35 weeks pregnant guide lists the other checks that week, and our due date calculator shows when your 35 to 37 week window falls.

If your swab is positive: antibiotics in labour

A positive result doesn't change your pregnancy care before labour. It changes what happens once labour begins, as KKH sets out below.

Penicillin is the antibiotic of choice. KKH gives a suitable alternative if you're allergic, so make sure your allergy is in your notes and your birth plan. The drip starts as soon as possible after labour begins or your waters break, so don't wait at home once either happens if you're a carrier.

Which babies are at higher risk

KKH lists four things that raise a baby's chance of GBS infection:

• Being born before 37 weeks
• An older brother or sister who had GBS infection
• A fever in the mother during labour
• Waters broken for a long time, especially more than 18 hours before the baby is born

After birth: how your baby is watched

Most babies with GBS infection become unwell in the first week of life, which doctors call early-onset infection. KKH says most infected babies show symptoms within 12 to 24 hours of birth, so babies at risk are watched closely in hospital. If infection is suspected, tests may include blood tests, fluid from around the spinal cord (a lumbar puncture) or a chest X-ray. Treatment starts straight away, because the infection can spread fast. Babies who develop it need antibiotics through a drip for at least 10 to 14 days, or up to 21 days with meningitis.

Late-onset GBS infection is less common and can appear up to three months of age. KKH notes that antibiotics in labour lower the risk of early-onset infection but don't prevent late-onset infection. That's why the warning signs below matter after you go home.

Breastfeeding and future pregnancies

You can breastfeed if you carry GBS. KKH says breastfeeding hasn't been shown to raise the risk of GBS infection, and it benefits you and your baby. Our breastfeeding support guide lists where to get help.

If a baby of yours has had GBS infection, tell your doctor early in your next pregnancy, because KKH offers antibiotics in labour to every mother in that situation.

When to go to the hospital

If you're a known carrier, head in as soon as your waters break or labour starts, so antibiotics can begin early. At KKH, from 22 weeks of pregnancy, leaking waters, bleeding or signs of labour go straight to the Delivery Suite, which is on Level 2 of the Women's Tower. Our signs of labour guide explains what to look out for, and our 37 weeks pregnant guide covers newborn warning signs.

Frequently asked questions

Is group B strep a sexually transmitted infection?

No. KKH says GBS is not sexually transmitted. About one in five women carry it, usually with no symptoms.

When is the GBS test done in pregnancy?

At KKH, between 35 and 37 weeks, for every woman planned for a vaginal birth. It's a quick vaginal or rectal swab, with results in one to two days at the KKH lab.

What happens if I test positive for GBS?

You're offered antibiotics through a drip once labour starts or your waters break, repeated every four hours until your baby is born. If your waters break after 37 weeks, KKH offers induction straight away.

Do I need antibiotics if I'm having a planned caesarean?

Not for GBS, unless labour has started or your waters have broken. You'll still get antibiotics at the operation to prevent wound infection.

Can GBS hurt my baby after we go home?

Late-onset GBS infection can appear up to three months of age, and antibiotics in labour don't prevent it. Get help immediately if your baby has trouble breathing, a fever or low temperature, poor feeding, fits or unusual sleepiness.

Can I breastfeed if I carry GBS?

Yes. KKH says breastfeeding hasn't been shown to increase the risk of GBS infection.