Antibiotics in Labour

Several factors can increase the risk of infection in term newborn babies, prompting the need for antibiotics in labour. These include the presence of bacteria in the vagina, including group B streptococcus (24), if your waters break more than 24 hours before your baby is born or high temperatures in the mother during labour. Under these circumstances, we recommend intravenous antibiotics (antibiotics into your vein, or IVAB’s) in labour for the safety of you and your baby. Antibiotics fight infection. They either kill bacteria or prevent them from reproducing and growing. Antibiotics can save lives and improve the health outcomes of both mothers and babies. However, antibiotics in labour can have adverse effects. It’s recommended you speak with your health professional and weigh up the pros and cons carefully considering your situation.  

Preterm Labour

Early labour and birth (before 37 weeks) may be due to an unknown infection. It may also be due to your waters breaking early. Certain antibiotics given to women whose waters have broken early will reduce the risk of infection in these babies. Babies born too early are more likely to need medical help in the early days and sometimes throughout life. We recommend IVAB’s for all women in preterm labour (25).  

Caesarean sections

Women who birth their baby via caesarean section are at risk of developing infections after their surgery, which can complicate their recovery. Antibiotics are administered in theatre by the anaesthetist as a preventative treatment (26). Women are encouraged to talk to their health care providers about their treatment options. You must consider the risks and benefits in light of your situation.  

Group B Strep (GBS)

Group B streptococcus (27) is a variety of bacteria found in the gut, vagina and urethra. It is detected in people of all ages and sexes worldwide and is usually asymptomatic (you don’t even know you have it). It is not a sexually transmitted infection; however, people can become colonised with GBS through sexual contact. GBS bacteria are part of the normal microbiome in up to a third of people;  they colonise the vagina of about 25% of women. The life cycle of the GBS bacteria is said to be 4-6 weeks. This cycle means that women who have a GBS colony can still test negative from time to time. To read more about GBS please click here.

GBS and your baby

Half of the babies born to women with GBS also become colonised with the bacteria. The most common means of infection is through contact with GBS from the mother’s vagina; however, it is also transmissible through contact with the mother’s skin and the breastmilk. For 98-99% of babies, this presents no problem. The bacteria become part of their normal microbiome. However, 1-2% of babies will develop a GBS INFECTION rather than a GBS COLONY. A GBS infection can have severe consequences for your baby and has a high mortality rate (10%). Babies with severe infection can also suffer long term consequences (27).  

What are the odds?

In a hospital birthing 5000 women per year:  

  • 25% will be GBS positive = 1250 women per year  
  • 50% of those babies colonise GBS = 625 babies per year  
  • 1-2% of those babies will develop GBS infection = 6.25-12.5 babies year  
  • 10% of those babies will die = 0.625 – 1.25 babies per year (1 baby in a 7.5-15 month period.)

In real terms, this means if we knew the GBS status of every woman birthing in that facility and didn’t treat any of them we would lose one baby a year to GBS infection. While these seem like long odds (1:5000), losing one baby a year to a potentially preventable disease is unthinkable.  

Do antibiotics in labour work?

Many studies suggest that the incidence of GBS infection in the first seven days of life of newborn babies is greatly reduced if the mother has had IVAB’s in labour. While much of the research done around GBS and IVAB’s is not considered gold standard or high level, medical research cannot ethically perform the required trials to provide this evidence.   Therefore, we advise women with risk factors for GBS to have IV antibiotics in labour. However, babies can still develop GBS in the first 7 days when a GBS positive mother has IVAB’s in labour. Babies can also develop EOGBSD when their mother has tested GBS negative.  

GBS infection risk factors

  • A baby born before 37 weeks of pregnancy has increased risk of a GBS infection than a baby born at term.  
  • You have had a previous baby with a GBS infection  
  • A high temperature develops (> 38 degrees C) in labour or within 24 hours of your baby being born  
  • Your waters break more than 18 hours before your baby is born  
  • A GBS screen during this pregnancy has come back positive.  

GBS screening

There are two ways to screen for GBS. The method of testing will depend on your maternity care provider.  

  • You have had a urine test in early pregnancy with your blood tests. This may involve a test for bacteria, including GBS. It may be found with routine testing if you have a urinary tract infection.  
  • A vaginal (or vaginal/rectal) swab which is either specific for GBS, or any bacterial infection.  

A GBS positive result in any of these tests will prompt the recommendation for IVAB’s in labour. Some health services perform universal screening by vaginal swab between 35-37 weeks of pregnancy. Others screen if there is a reason to do so.  

Informed consent

Whatever the method of screening, you should seek balanced information before consenting to the test.   This is for a few reasons:  

  • The testing can be uncomfortable and invasive (especially a vaginal or vaginal/ rectal swab – you can collect these yourself at your appointment to minimise discomfort).  
  • If your result is positive, you need to be aware of the recommended management. IVAB’s are invasive and the treatment itself is not free of risk.  

When considering this test, you need to know what you are going to do with the results. If you would decline treatment for yourself and/or your baby there is no point to testing. Additionally, if you are GBS positive and you decline treatment you may find that several health professionals will discuss your decision not to treat, and you may feel pressured into complying.  

Effective treatment

If you consent to IVAB’s in labour, we need to treat you to a level that the antibiotic gets to do its job. The antibiotics needed to prevent GBS disease depend on the drug being in the baby’s system for a certain length of time. Research has found that the level of antibiotic in your baby’s blood is at its highest 1 hour after administration.   This is because it needs to make its way from your blood, across the placenta and into the baby. Once it’s there it needs to stay high enough to prevent the bacteria from taking hold. To ensure we are keeping the antibiotic level in baby’s blood high enough, we will give you a high dose to start with followed by top-up doses every 2-4 hours (depending on your health service).   These antibiotics are most effective with at least 90 minutes to work. However, any treatment is better than none. Some strains of GBS bacteria have shown low levels of antibiotic resistance.  

Benefits and risks of antibiotics in labour


  • IVAB’s reduce the risk of GBS infection in the newborn baby from birth to 7 days of age
  • Reduces risk for GBS related infection in the unwell mother  


  • Anaphylaxis (allergic reaction to antibiotic) in mother  
  • Less severe reactions including rash  
  • Nausea  
  • Thrush (mother and baby)  
  • Adverse effect on the good bacteria in the system of mother and baby (the microbiome).  

Prolonged rupture of membranes

Doctors and midwives advise women that antibiotics may be necessary if their waters break a long time before they labour. This is to prevent infection of the uterus or amniotic sac (the sac around the baby), especially if GBS status is unknown. The time frame in which you will need antibiotics varies from hospital to hospital. Still, most will prefer to treat you around 18 hours after your waters have broken. Please ask your chosen provider what their policies are around IVAB’s under these circumstances (28).  


If you have a temperature during labour, we recommend IVAB’s, even if the cause of your fever is unknown. In the case you have an infection IVAB’s will reduce the risk of you passing it to your baby (29).  

IVAB’s (IntraVenous AntiBiotics in labour)

Antibiotics destroy bacteria that are dangerous to the baby during birth. The antibiotics are only effective during labour and birth only; you cannot take them before labour, because the bacteria can grow back swiftly.   The drug most commonly used in such treatment is Penicillin. Penicillin is very safe and effective at preventing the spread of Group B strep bacteria to newborns during birth. There are effective alternatives if you have a penicillin allergy. However, treating all colonized women exposes many women and infants to possible adverse effects, potentially without benefit. Giving antibiotics during labour can affect the bacterial colonisation of the newborn baby.   These bacteria are fundamental to your baby’s maturing immune system. Your baby may suffer future effects if this process is interrupted at such an early stage. It can also make women and babies more prone to thrush infections (30).  

Antibiotics in labour and your microbiome

If you have consented to antibiotics in labour how do you support yours and your baby’s microbiome? There is good news! Some research suggests that lactobacillus bacteria (such as you find in probiotics) can resist penicillin when under stressed conditions (such as during labour). If you have risk factors prompting antibiotics in labour, it may be a good idea to start taking probiotics before your labour. That way the good bacteria have a chance to make themselves at home (30). Probiotics after your birth will help to balance out your gut flora again.   Minimise your refined sugar intake after the baby is born, as the microbes responsible for thrush thrive on it. Starve them and the good bacteria in the probiotics will be able to control them again. Breastfeed your baby whenever possible. Colostrum and breast milk are full of good bacteria that are there to colonise your baby’s gut. Your milk is probiotics for baby.    

Sophie Schipplock (BN, MMid) Registered Nurse, Registered Midwife
Photo by PrinceOfLove used under license from Shutterstock.com