Toxoplasmosis

Pregnancy: the real risks and the sensible precautions

Toxoplasmosis is one of the standard worries of pregnancy, and most of the worry is misplaced. Here is what actually determines the risk, and what to do about it.

By Jeroen Saeij · Updated 17 September 2026

Why a first infection is what matters

Toxoplasma reaches the baby through the blood, and it is only in the blood during the first few weeks after a person is infected. After that the parasite retreats into dormant cysts, the immune system stands guard, and there is nothing in the bloodstream to cross the placenta. That is why public health agencies say the risk applies to women infected for the first time while pregnant or just before¹.

The corollary matters just as much: a woman who was infected before pregnancy is, with rare exceptions, protected for later pregnancies. The exceptions are a weakened immune system, and reinfection with a parasite strain very different from the first. A French case in which a previously immune mother transmitted an unusual South American strain to her baby, probably from imported raw horse meat, is the best documented example². My own lab showed in mice why this can happen: immunity built against one strain does not protect against many of the strains that circulate in South America³. Outside those situations, a positive antibody test from before pregnancy is reassuring news.

This protection should not be taken for granted, because a close relative of Toxoplasma does not grant it. In cattle, Neospora caninum reawakens during pregnancy in cows that were infected years earlier and crosses the placenta again and again, despite their immunity⁴. Why a past infection protects a woman and not a cow is one of the open questions in my field; the animals page explains what is known.

How likely is a first infection?

Less likely than the amount of worry suggests. In the United States about 7.5 percent of women of childbearing age carry antibodies⁵, so more than nine in ten are susceptible, yet new infections during any given pregnancy are uncommon. Rates are higher in countries where the parasite is common, and the risk is dominated by what you eat: in a study across six European cities, undercooked or cured meat accounted for between 30 and 63 percent of infections in pregnant women, contact with soil for 6 to 17 percent, and contact with cats for none⁶.

What happens if the parasite reaches the baby

Two things change in opposite directions as pregnancy progresses. The chance that an infected mother passes the parasite on rises steeply, from about 6 percent when infection occurs at 13 weeks to about 72 percent at 36 weeks. The severity for the baby falls just as steeply: infections early in pregnancy are rarely transmitted but often serious when they are, while infections late in pregnancy are usually transmitted but usually silent. These figures come from more than 600 confirmed maternal infections followed in Lyon, France, where the overall transmission rate was 29 percent⁷.

The consequences of congenital infection range from none at all to eye disease, which can appear years later, and damage to the brain⁸¹. The eye lesions are the most common lasting problem and, as with everything about this parasite, they are more frequent and more severe in Brazil than in Europe⁹.

Testing: what it can and cannot tell you

A blood test can show whether you have antibodies to the parasite, and an additional test called avidity can often tell whether an infection is old or recent¹⁰. What a single positive result cannot do is tell you the date of your infection with certainty, which is exactly the question that matters in pregnancy. The blood tests page explains how the pieces fit together and why a “recent infection” result deserves confirmation by a specialist laboratory before anyone acts on it.

Countries differ sharply on screening. France has tested every non-immune pregnant woman monthly since 1992¹¹. The United States and the United Kingdom do not screen routinely, partly because infection is rarer there and partly because the benefit of prenatal treatment is less certain than one would like¹². If you want to know your status before or early in pregnancy, ask for the test. Knowing you are already immune ends the worry, and knowing you are susceptible tells you which precautions are worth keeping.

Treatment during pregnancy

If a first infection is diagnosed during pregnancy, treatment is offered to reduce the chance of transmission or the damage from it. The honest summary of the evidence is that it probably helps and certainly is not a guarantee. A large analysis of European screening programs found weak evidence that treatment started within three weeks of infection reduced transmission, and no clear evidence that it reduced symptoms in babies who were infected anyway¹². The one randomized trial to date compared the two standard regimens and found fewer infected babies and no brain lesions with the stronger combination, but enrollment was stopped early and the difference did not reach statistical significance¹³. Decisions here belong with an obstetrician and an infectious disease specialist, ideally with a reference laboratory confirming the timing of infection first.

The precautions that work

Since most infections come from food and the environment, that is where prevention lives¹⁴⁶¹⁵:

• Cook meat thoroughly. Whole cuts to at least 63 °C (145 °F) with a three-minute rest, ground meat to 71 °C (160 °F), poultry to 74 °C (165 °F). Use a thermometer. Color is not a reliable guide.
• Or freeze it first. Several days at −18 °C (0 °F), the setting of a household freezer, kills the parasite’s cysts in meat.
• Be wary of cured, dried and smoked meats unless they are commercially produced. Locally made products were a significant risk in the American study.
• Wash fruit and vegetables, and wash your hands and cutting boards after handling raw meat or unwashed produce.
• Wear gloves for gardening and wash your hands afterwards. Cover children’s sandboxes.
• Skip raw oysters, clams and mussels, unpasteurized goat’s milk, and untreated water.
• The litter box: have someone else change it if possible; otherwise wear gloves, change it daily, and wash your hands. A daily change works because oocysts need at least a day after leaving the cat to become infectious. Keep the cat indoors and feed it commercial food, and it is very unlikely to be shedding at all.

Nothing on this list requires giving up a cat, a garden or a barbecue. It requires a thermometer, a freezer, and a habit of washing things.

Sources

1. Centers for Disease Control and Prevention. People at Increased Risk for Toxoplasmosis. Accessed 17 September 2026.
2. Elbez-Rubinstein A, Ajzenberg D, Dardé ML et al. Congenital toxoplasmosis and reinfection during pregnancy: case report, strain characterization, experimental model of reinfection, and review. J Infect Dis 2009;199:280-5. PubMed · DOI
3. Jensen KD, Camejo A, Melo MB et al. Toxoplasma gondii superinfection and virulence during secondary infection correlate with the exact ROP5/ROP18 allelic combination. mBio 2015;6:e02280. PubMed · DOI
4. Williams DJ, Hartley CS, Björkman C et al. Endogenous and exogenous transplacental transmission of Neospora caninum - how the route of transmission impacts on epidemiology and control of disease. Parasitology 2009;136:1895-900. PubMed · DOI
5. Jones JL, Kruszon-Moran D, Elder S et al. Toxoplasma gondii Infection in the United States, 2011-2014. Am J Trop Med Hyg 2018;98:551-557. PubMed · DOI
6. Cook AJ, Gilbert RE, Buffolano W et al. Sources of toxoplasma infection in pregnant women: European multicentre case-control study. European Research Network on Congenital Toxoplasmosis. BMJ 2000;321:142-7. PubMed · DOI
7. Dunn D, Wallon M, Peyron F et al. Mother-to-child transmission of toxoplasmosis: risk estimates for clinical counselling. Lancet 1999;353:1829-33. PubMed · DOI
8. Montoya JG, Remington JS. Management of Toxoplasma gondii infection during pregnancy. Clin Infect Dis 2008;47:554-66. PubMed · DOI
9. Gilbert RE, Freeman K, Lago EG et al. Ocular sequelae of congenital toxoplasmosis in Brazil compared with Europe. PLoS Negl Trop Dis 2008;2:e277. PubMed · DOI
10. Liesenfeld O, Montoya JG, Kinney S et al. Effect of testing for IgG avidity in the diagnosis of Toxoplasma gondii infection in pregnant women: experience in a US reference laboratory. J Infect Dis 2001;183:1248-53. PubMed · DOI
11. Peyron F, L'ollivier C, Mandelbrot L et al. Maternal and Congenital Toxoplasmosis: Diagnosis and Treatment Recommendations of a French Multidisciplinary Working Group. Pathogens 2019;8. PubMed · DOI
12. Thiébaut R, Leproust S, Chêne G et al. Effectiveness of prenatal treatment for congenital toxoplasmosis: a meta-analysis of individual patients' data. Lancet 2007;369:115-22. PubMed · DOI
13. Mandelbrot L, Kieffer F, Sitta R et al. Prenatal therapy with pyrimethamine + sulfadiazine vs spiramycin to reduce placental transmission of toxoplasmosis: a multicenter, randomized trial. Am J Obstet Gynecol 2018;219:386.e1-386.e9. PubMed · DOI
14. Centers for Disease Control and Prevention. Preventing Toxoplasmosis. Accessed 17 September 2026.
15. Jones JL, Dargelas V, Roberts J et al. Risk factors for Toxoplasma gondii infection in the United States. Clin Infect Dis 2009;49:878-84. PubMed · DOI