Patient information from BMJ

Toxoplasmosis in pregnancy: what is it?

Last published:Feb 01, 2022

Toxoplasmosis is a common infection that can be passed on by cats. It doesn't usually make people ill. But it can harm your baby if you catch it when you're pregnant.

What is toxoplasmosis?

Toxoplasmosis is caused by a parasite. Parasites live inside the bodies of other living things. The toxoplasmosis parasite lives mainly in cats, although it can also infect other animals and people.

When cats are infected, the parasite comes out in their stools, and into litter boxes or soil, where it can infect you if you come in contact with it.

You can also be infected if you eat undercooked meat or drink water that contains the parasite.

Once you're infected, the toxoplasmosis parasite lives in your body but it doesn’t usually cause problems. Your immune system protects you by keeping it in check. And if you've had toxoplasmosis several months or more before becoming pregnant, your unborn baby will be protected, too.

But if you get toxoplasmosis while you are pregnant, or just before, it can cause serious health problems for your unborn baby.

Not all babies get infected. The risk of your baby getting toxoplasmosis is lowest if you are infected in early pregnancy and highest if you are infected in late pregnancy.

But babies who do get infected early in the pregnancy are more likely to have serious health problems.

Also, if you become infected in early pregnancy you may have a miscarriage (lose your baby).

How do I know if I have toxoplasmosis?

Most healthy people, including pregnant women, don't have any symptoms from toxoplasmosis. Some people have a mild flu-like illness for a few weeks.

In some countries (such as France) doctors routinely test women who are pregnant, or could become pregnant, for toxoplasmosis.

But many countries (including the UK and the US) don't routinely check women for the parasite.

If you're pregnant and are concerned that you may have become infected, you can have a blood test. If your test suggests you have recently been infected, the next step is to find out whether the infection has passed to your baby.

Your doctor may suggest having a test called amniocentesis. Doctors take a sample of the amniotic fluid (the fluid that surrounds your baby in the womb) by putting a needle into your abdomen. They check the fluid for signs of infection.

This test is usually reliable, but it is not completely safe for your baby, as there is a small risk of miscarriage. You'll need to discuss this with your doctor.

Amniocentesis doesn't show how toxoplasmosis may be affecting your baby. If the test is positive for the infection, your doctor will use an ultrasound to look for possible problems.

Unborn babies who have toxoplasmosis usually look normal on ultrasound scans. But sometimes they show signs of problems related to the infection.

What will happen to my baby?

If you get toxoplasmosis just before or during your pregnancy, your baby will be tested for the infection after birth and checked for any problems related to the infection.

Some babies with toxoplasmosis have signs of a severe infection at the time of birth. For example, they may have an eye infection, an enlarged liver and spleen, jaundice (yellowing of the skin and eyes), or pneumonia.

If a baby was infected early in pregnancy, they may be blind or have other problems related to their development in the womb. Distressingly, some babies are stillborn or die a few days after birth.

However, most babies with toxoplasmosis seem normal at birth. But many will have some health problems months or even years later. These may include:

• eye infections

• hearing problems

• seizures

• learning difficulties, and

• delayed growth.

Treatment can help reduce the chance of these problems happening.

An eye infection called chorioretinitis is the most common long-term health problem caused by toxoplasmosis. It can permanently damage a baby's eyesight.

If your baby has eye problems, he or she will need to be treated by an eye specialist. New eye infections and sight problems can happen through childhood and even later. Your baby will have regular checks of their eyes and of their hearing.

You can still breastfeed if you have toxoplasmosis. Doctors think it's unlikely that the infection would spread to the baby from breastfeeding. The parasite that causes the infection has never been found in human breast milk.

If you had toxoplasmosis during a previous pregnancy, you will not be at risk of passing the infection on to your baby in a future pregnancy, as long as your immune system is healthy.

For more information on treatments for toxoplasmosis see our leaflet Toxoplasmosis in pregnancy: what treatments work?