Toxoplasmosis Before Pregnancy: Can I Pass It to My Baby?

For the vast majority of healthy women, the answer is a reassuring “no.” If you contracted toxoplasmosis and fully recovered at least six months before becoming pregnant, your immune system has developed strong, lasting protection. For a mother with a healthy immune system, the risk of passing the parasite to the baby from a past infection is virtually zero.

How Prior Immunity Protects Your Baby

When you are infected with Toxoplasma gondii—the parasite that causes toxoplasmosis—your immune system fights off the active infection. As part of this process, your body creates “memory” proteins called Immunoglobulin G (IgG) antibodies. These antibodies remain in your bloodstream for the rest of your life ^[1][2].

If you are exposed to the parasite again during your pregnancy, your IgG antibodies recognize the threat immediately. They neutralize the parasite before it has a chance to cross the placenta and reach your growing baby ^[1][2].

Because of this built-in defense system, congenital toxoplasmosis (when the infection is passed to the fetus in the womb) almost exclusively happens when a mother is infected with the parasite for the very first time during her pregnancy ^[1][2].

(Note: Even if you are immune to toxoplasmosis, you must still follow standard pregnancy precautions—such as thoroughly cooking meat, washing vegetables, and having someone else change the litter box. Other dangerous pathogens, like Listeria and Salmonella, can still be found in undercooked meat or animal waste.)

The Rare Exceptions: Weakened Immune Systems

While prior immunity provides excellent protection, there are a few crucial exceptions to be aware of:

1. Severe Immune Suppression
After your initial infection clears, the Toxoplasma parasite doesn’t completely leave your body; it forms microscopic, dormant cysts in your tissues that are kept perfectly in check by a healthy immune system. However, if your immune system becomes severely suppressed, the dormant infection can become active again ^[3][4]. If this reactivation occurs during pregnancy, the active parasite can enter the bloodstream and potentially cross the placenta to infect the baby ^[4].

Conditions that might cause this level of immune suppression include:

• Advanced HIV/AIDS: Specifically when CD4 T-cell counts are very low ^[3].
• Organ Transplants: The potent anti-rejection medications required after a transplant severely suppress the immune system.
• Aggressive Chemotherapy: Certain strong cancer treatments can wipe out immune defenses.

Note: Not all medications that affect the immune system carry this risk. For instance, studies suggest that targeted biological therapies known as TNF-alpha blockers (such as Remicade or Humira, used for autoimmune diseases) do not significantly impair the immune system’s ability to keep the parasite dormant ^[5].

2. A New, Virulent Strain
In extremely rare cases, a healthy woman with prior immunity might be reinfected if she is exposed to a completely different, highly virulent strain of the parasite (such as certain strains found in parts of South America).

What This Means For You

If you are generally healthy and had toxoplasmosis more than six months prior to conception, you can take comfort in knowing your baby is protected by your past infection.

To be absolutely sure of your immune status, your doctor can perform a simple blood test. If your results come back “positive,” do not panic! Doctors look at two different types of antibodies: IgG (which indicates an old, safe, protective infection) and IgM (which indicates a recent, active infection) ^[6][7]. If it is unclear exactly when your infection occurred, your doctor can also order an avidity test (a test that helps pinpoint the timeline of the infection), which confirms whether the infection happened safely before you conceived.