Pregnancy information

Pregnancy infections

Throughout life, we all encounter many viruses and bacteria.

This page is about infections that can cause problems in pregnancy, their symptoms and what to do if you're worried.

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 90% of women are immune to chickenpox. 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 does, speak to your GP, obstetrician or midwife immediately. A blood test will find out if you're immune.

CMV in pregnancy

CMV (cytomegalovirus) is a common virus that's part of the herpes group, which can also cause cold sores and chickenpox. CMV infections are common in young children.

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 had the infection before.

It's not always possible to prevent a CMV infection, but you can reduce the risk by: 

  • washing your hands regularly with soap and hot water, particularly if you have been changing nappies, or work in a nursery or daycare 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 cutlery 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 symptoms of CMV.

Group B streptococcus in pregnancy

Group B streptococcus (GBS, or group B strep) is carried by up to 30% of people, but it rarely causes harm or symptoms. In women, the bacteria are found in the intestine and vagina.

It causes no problem in most pregnancies but, in a small number, group B strep 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. You should also be offered them during labour if you've had a group B strep urinary tract infection during the pregnancy.

GBS infection of the baby is more likely 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 should be offered 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 5 minutes
  • avoid close contact with sick cats
  • even if you don't have a cat, wear gloves when gardening in case the soil is contaminated with faeces
  • 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


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, as well all contact with newborn lambs. Tell your doctor if you experience flu-like symptoms after coming into contact with sheep.


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's no risk of hepatitis E from eating cooked pork products.

Hepatitis B in pregnancy

Hepatitis B is a virus that infects the liver. Many people with hepatitis B will show no sign of illness, but they 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.

Hepatitis C in pregnancy

Hepatitis C 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're infected, they can be referred for specialist assessment.

Herpes in pregnancy

Genital herpes infection can be dangerous for a newborn baby.

You can get herpes 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 outbreaks 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 on to your baby.

If you or your partner have herpes, use condoms or avoid sex during an outbreak. Avoid oral sex if you or your partner have cold sores or genital sores (active genital herpes).

Tell your midwife or doctor if either you or your partner have recurring herpes or develop sores.

HIV in pregnancy

You'll be offered a confidential HIV 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.

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're diagnosed with HIV, you and your doctor will need to discuss the management of your pregnancy and birth to reduce the risk of infection for 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 regular intervals for up to 2 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, or 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 and causes a characteristic red rash on the face, so it's often called "slapped cheek syndrome"

Although 60% of women are immune, 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 (German measles) is rare in the UK thanks to the high uptake of MMR (measles, mumps and rubella) vaccination.

But if you develop rubella in the first 4 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.

If you're pregnant and aren't sure whether you've had 2 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 6-week postnatal check after the birth. This will protect you in any future pregnancies.

MMR vaccine cannot be given during pregnancy.

STIs in pregnancy

STIs often have no symptoms, so you may not know if you have one. However, many STIs can affect your baby's health both 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, you can also visit a Brook centre for free confidential advice.

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 go 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.

Last Updated: 12/07/2023 10:57:02
The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website