Pregnancy Guide


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.


If you catch rubella (German measles) in the first four months of pregnancy it can seriously affect your baby's sight and hearing, and cause brain and heart defects.

All children are now offered a vaccine against rubella through the MMR immunisation when they are 13 months old and a second immunisation before they start school.

If you are not immune and you do come into contact with rubella, tell your doctor at once. Blood tests will show whether you have been infected and you'll be able to decide what action to take.

CMV in pregnancy

CMV is a common virus that is one 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 is 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 is better to kiss them on the head or give them a hug
not sharing food or eating utensils with young children, or 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 and how CMV affects babies (congenital CMV).

Sexually transmitted infections

Sexually transmitted infections (STIs) are on the increase and the most common is chlamydia. 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 that you or your partner may have an STI, go for a check-up as soon as possible. You can ask your doctor or midwife or, if you prefer, go to a genito-urinary medicine (GUM) clinic or sexual health clinic. Your confidentiality is guaranteed.

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



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.

Find out about coping with a positive HIV test. You can also go to a sexual health clinic for an HIV test and advice.

Current evidence suggests that an HIV-positive mother in good health and without symptoms of the infection is unlikely to be adversely affected by pregnancy. HIV-positive mothers can pass on the virus through breastmilk.

However, it's possible to reduce the risk of transmitting HIV to your baby during pregnancy and after birth. The page on antenatal checks and tests has more information about these risks.

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 Royal College of Obstetricians and Gynaecologists has more information on HIV and pregnancy.

Hepatitis B

Hepatitis B

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 at birth is 90-95% effective in preventing them from getting hepatitis B and developing long-term infection. The first dose is given within 24 hours of birth, and two more doses are given at one and two months, with a booster dose at 12 months.

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

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

In people who take illegal drugs, this can be as 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 hepatitis B or HIV. This cannot be prevented at present. Your baby can be tested for hepatitis C and, if your baby is infected, he or she can be referred for specialist assessment.


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.


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. If you've never had chickenpox (or if you're unsure 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.


You can catch toxoplasmosis through contact with cat faeces. If you are pregnant the infection can damage your baby so take precautions (see infections transmitted by animals, further down the page, or 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 are infected while you're pregnant, treatment for toxoplasmosis is available.

Parvovirus B19 (slapped cheek disease)

Parvovirus B19 infection is common in children and causes a characteristic red rash on the face, so it's often called slapped cheek disease.

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 check whether you are immune through a blood test. In most cases, the baby is not affected when a pregnant woman is infected with parvovirus.

Group B streptococcus

Group B streptococcus (GBS, or group B strep) is a bacterium carried by up to 30% of people but causes no 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 with GBS (cystitis) during the pregnancy, you should also be offered antibiotics in labour.

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

  • your labour is premature (before 37 weeks of pregnancy)
  • your waters break early
  • you have a fever during labour, or
  • your 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 if you have concerns. Talk to your doctor or midwife.

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 no one 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 (even if you don't have a cat) 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, 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 tocoplasma. 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 going on 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.

Last Updated: 08/03/2021 07:16:53
The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website