Your pregnancy and baby guide

Infections in pregnancy that may affect your baby

Throughout life, we all come into contact with many viruses and bacteria. As part of our defence mechanism, the body makes antibodies to help fight infection.

If you have antibodies against a particular virus or bacteria, you are immune, and the antibodies help to prevent or reduce the impact of getting the infection again.

This page is about infections that can cause problems in pregnancy.

Chickenpox in pregnancy

Chickenpox infection in pregnancy can be dangerous for both mother and baby, so it's important to seek advice early if you think you may have chickenpox.

Around 95% of women are immune to chickenpox infection. But if you've never had chickenpox (or you're unsure if you've had it) and you come into contact with a child or adult who has it, speak to your GP, obstetrician or midwife immediately. A blood test will establish if you are immune.

Find out about the complications of chickenpox for you and your unborn baby, and watch this video explaining what to do if you're exposed to chickenpox in pregnancy.

CMV in pregnancy

CMV is a common virus and is part of the herpes group of viruses, which can also cause cold sores and chickenpox.

Infection can be dangerous during pregnancy, as it can cause problems for unborn babies, such as hearing loss, visual impairment or blindness, learning difficulties and epilepsy.

CMV is particularly dangerous to the baby if the pregnant mother has not previously had the infection at some point in her life.

It's not always possible to prevent a CMV infection, but you can take some steps to reduce the risk. CMV infections are common in young children. 

You can reduce the risk of infection with some simple steps, such as:

  • washing your hands regularly using soap and hot water, particularly if you have been changing nappies or if you work in a nursery or day-care centre
  • not kissing young children on the face – it's better to kiss them on the head or give them a hug
  • not sharing food or eating utensils with young children, and not drinking from the same glass as them

These precautions are particularly important if you have a job that brings you into close contact with young children. In this case, you can have a blood test to find out whether you have previously been infected with CMV.

Find out more about:

Group B streptococcus in pregnancy

Group B streptococcus (GBS, or group B strep) is a bacteria carried by up to 30% of people, but it rarely causes harm or symptoms. In women, it's found in the intestine and vagina, and causes no problem in most pregnancies.

In a small number of pregnancies, it infects the baby, usually just before or during labour, leading to serious illness.

If you've already had a baby who had a GBS infection, you should be offered antibiotics during labour to reduce the chances of your new baby getting the infection.

If you have had a group B streptococcal urinary tract infection during the pregnancy, you should also be offered antibiotics in labour.

GBS infection of the baby is more likely to occur if:

  • you go into premature labour (before 37 weeks of pregnancy)
  • your waters break early
  • you have a fever during labour
  • you currently carry GBS

Your midwife or doctor will assess whether you need antibiotics during labour to protect your baby from being infected.

It's possible to be tested for GBS late in pregnancy. Talk to your doctor or midwife if you have concerns.

Infections transmitted by animals


Cat faeces may contain toxoplasma – an organism that causes toxoplasmosis infection. Toxoplasmosis can damage your baby. To reduce the risk of infection:

  • Avoid emptying cat litter trays while you're pregnant.
  • If nobody else can empty the litter tray, use disposable rubber gloves. Trays should be cleaned daily and filled with boiling water for five minutes.
  • Avoid close contact with sick cats.
  • Wear gloves when gardening in case the soil is contaminated with faeces, even if you don't have a cat.
  • Wash your hands and gloves after gardening.
  • If you do come into contact with cat faeces, wash your hands thoroughly.
  • Follow general food hygiene rules. See how to prepare food safely and how to store food safely.


Lambs and sheep can carry an organism called Chlamydia psittaci, which is known to cause miscarriage in ewes. They also carry toxoplasma. Avoid lambing or milking ewes, and all contact with newborn lambs. If you experience flu-like symptoms after coming into contact with sheep, tell your doctor.


Research is ongoing to see if pigs can be a source of hepatitis E infection. This infection is dangerous in pregnant women, so avoid contact with pigs and pig faeces. There is no risk of hepatitis E from eating cooked pork products.

Hepatitis B

The Hepatitis B virus is a virus that infects the liver. Many people with hepatitis B will show no sign of illness, but can be carriers and may infect others.

The virus is spread by having sex with an infected person without using a condom, and by direct contact with infected blood. If you have hepatitis B, or are infected during pregnancy, you can pass the infection on to your baby at birth.

All pregnant women are offered a blood test for hepatitis B as part of their antenatal care. Babies who are at risk should be given the hepatitis B vaccine at birth to prevent infection and serious liver disease later on in life. Immunisation from birth is 90-95% effective in preventing babies developing long-term hepatitis B infection.

The first dose is given within 24 hours of birth. Further doses are given at 4, 8 weeks, 12 and 16 weeks, and a final dose at 12 months to provide long-lasting protection. A few babies may also need an injection of antibodies, called immunoglobulin, soon after birth.

Your baby will be tested for hepatitis B infection at 12 months. Any babies who have become infected should be referred for specialist assessment and follow-up.

Hepatitis C

The Hepatitis C virus infects the liver. Many people with hepatitis C have no symptoms and are unaware they are infected. The virus is transmitted by direct contact with infected blood.

In people who take illegal drugs, this can be a result of sharing blood-contaminated needles and drug-injecting equipment. People who received a blood transfusion in the UK prior to September 1991, or blood products prior to 1986, may also be at risk.

Hepatitis C can also be transmitted by receiving medical or dental treatment in countries where hepatitis C is common and infection control may be poor, or by having sex with an infected partner.

If you have hepatitis C, you may pass the infection on to your baby, although the risk is much lower than with hepatitis B or HIV. This cannot currently be prevented. Your baby can be tested for hepatitis C and, if they are infected, they can be referred for specialist assessment.

Herpes in pregnancy

Genital herpes infection can be dangerous for a newborn baby. It can be caught through genital contact with an infected person or from oral sex with someone who has cold sores (oral herpes). Initial infection causes painful blisters or ulcers on the genitals. Less severe attacks usually occur for some years afterwards.

Treatment is available if your first infection occurs in pregnancy. If your first infection occurs near the end of pregnancy or during labour, a caesarean section may be recommended to reduce the risk of passing herpes to your baby.

If you or your partner have herpes, use condoms or avoid sex during an attack. Avoid oral sex if you or your partner have cold sores or genital sores (active genital herpes). Tell your doctor or midwife if either you or your partner have recurring herpes or develop the symptoms described above.

HIV in pregnancy

You'll be offered a confidential HIV (human immunodeficiency virus) test as part of your routine antenatal care. Your midwife or doctor will discuss the test with you, and counselling will be available if the result is positive.

Read more about screening for HIV in pregnancy.

Find out about coping with a positive HIV test.

Current evidence suggests an HIV-positive mother in good health and without symptoms of the infection is unlikely to be adversely affected by pregnancy.

However, HIV can be passed from a pregnant woman to her baby during pregnancy, birth or breastfeeding.

If you are diagnosed with HIV, you and your doctor will need to discuss the management of your pregnancy and birth to reduce the risk of infection to your baby.

Treatment in pregnancy greatly reduces the risk of passing on HIV to the baby – from 1 in 4 to fewer than 1 in 100.

Your baby will be tested for HIV at birth and at intervals for up to two years.

You'll be advised not to breastfeed, as HIV can be transmitted to your baby in this way.

If you're HIV positive, talk to your doctor or midwife about your own health and the options open to you. You can also contact organisations such as Positively UK or the Terrence Higgins Trust for information and support. The British HIV Association has more information on HIV and pregnancy.

Parvovirus B19 (slapped cheek syndrome) in pregnancy

Parvovirus B19 infection is common in children. It causes a characteristic red rash on the face so is often called "slapped cheek syndrome".

Although 60% of women are immune to this infection, parvovirus is highly infectious and can be harmful to the baby. If you come into contact with anyone who is infected, you should talk to your doctor, who can carry out a blood test to check whether you're immune. In most cases, the baby is not affected when a pregnant woman is infected with parvovirus.

Rubella in pregnancy

Rubella is rare in the UK thanks to the high uptake of MMR (measles, mumps and rubella) vaccination.

But if you develop rubella (German measles) in the first four months of pregnancy, it can lead to serious problems, including birth defects and miscarriage.

If you're pregnant, you should contact your GP or midwife as soon as possible if:

  • you come into contact with someone who has rubella
  • you have a rash or come into contact with anyone who does
  • you have symptoms of rubella

It's unlikely you have rubella in these circumstances, but you may need a blood test to check for the condition.

If you're pregnant and aren't sure you've had two doses of the MMR vaccine, ask your GP practice to check your vaccination history.

If you haven't had both doses or there's no record, you should ask for the vaccine when you go for your six-week postnatal check after the birth. This will protect you in any future pregnancies.

MMR vaccination cannot be given during pregnancy.

STIs in pregnancy

STIs are on the increase, and chlamydia is the most common type. STIs often have no symptoms, so you may not know if you have one. However, many STIs can affect your baby's health during pregnancy and after the birth.

If you have any reason to believe you or your partner may have an STI, go for a check-up as soon as possible. You can ask your GP or midwife. If you prefer, you can go to a genitourinary medicine (GUM) clinic or sexual health clinic. Confidentiality is guaranteed.

Find a sexual health service near you, including GUM or sexual health clinics.

If you're under 25 years old, you can also visit a Brook centre for free confidential advice, or you can contact the National Chlamydia Screening Programme for a free confidential test. You may also be able to order a free chlamydia test online.

Toxoplasmosis in pregnancy

You can catch a toxoplasmosis infection through contact with cat faeces. If you're pregnant, the infection can damage your baby, so take precautions – see Infections transmitted by animals or our page on preventing toxoplasmosis. Most women have had the infection before pregnancy and will be immune.

If you feel you may have been at risk, discuss it with your GP, midwife or obstetrician.

If you're infected while pregnant, treatment for toxoplasmosis is available. This can reduce the risk of the baby becoming infected. Where the baby is infected, treatment may reduce the risk of damage.

Zika virus

There's evidence the Zika virus causes birth defects if a woman catches it when she's pregnant. In particular, it can cause the baby to have an abnormally small head (microcephaly).

Zika does not naturally occur in the UK. Seek travel health advice before your trip if you plan to travel to an affected area, such as:

  • South or Central America
  • the Caribbean
  • southeast Asia
  • the Pacific region – for example, Fiji

It's recommended that pregnant women postpone non-essential travel to high-risk areas. Check the A-Z list of countries and their level of Zika risk to see which are affected.

Zika virus is spread by mosquitoes. You can reduce your risk of mosquito bites by using insect repellent and wearing loose clothing that covers your arms and legs.

Media last reviewed: 29 Nov 2017

Media review due: 29 Nov 2020

Page last reviewed: 28/01/2015
Next review due: 30/01/2018