Cat poop can contain a parasite called Toxoplasma gondii that, if transmitted to an unborn baby, can cause serious birth defects including brain damage, vision loss, and developmental delays. The risk isn’t from cats themselves but specifically from contact with infected feces, and the danger is highly preventable with a few simple precautions.
The Parasite Behind the Risk
Toxoplasma gondii is a microscopic parasite that uses cats as its primary host. When a cat eats infected prey (a mouse, bird, or other small animal) or raw meat, the parasite reproduces inside the cat’s digestive tract and produces tiny egg-like structures called oocysts. An infected cat can shed millions of these oocysts in its feces over a period of about 10 to 14 days.
Here’s a critical detail: freshly deposited oocysts aren’t immediately dangerous. They need one to five days sitting in the environment before they become infectious through a maturation process called sporulation. That 24-hour minimum window is the basis for the most important safety advice: scoop the litter box daily and you dramatically reduce the chance of exposure.
Once oocysts mature, though, they’re remarkably hardy. In damp soil, nearly 44% of oocysts remain viable after 100 days. Under dry conditions they survive less well, but researchers have detected them more than 400 days after they were deposited. This is why gardening in soil where cats have been is also a risk, not just the litter box itself.
What Toxoplasmosis Can Do to a Baby
Most healthy adults who contract toxoplasmosis never notice. They might feel mildly flu-ish or have no symptoms at all. The immune system usually keeps the parasite in check. But during pregnancy, if the parasite crosses the placenta and reaches the developing baby, the consequences can be severe. This is called congenital toxoplasmosis, and it can cause:
- Eye and vision problems, including inflammation of the retina that can lead to partial or complete vision loss
- Fluid buildup in the brain (hydrocephalus), which increases pressure inside the skull
- Calcium deposits in the brain, visible on imaging and associated with neurological damage
- An abnormally large or small head
- Seizures
- Hearing loss
- Developmental delays
- Jaundice, rash, or enlarged liver and spleen
Some of these signs appear at birth. Others don’t show up until months or years later, particularly the eye problems, which can emerge in childhood or even adolescence in babies who seemed healthy at delivery.
Timing Matters: Risk by Trimester
The likelihood that the parasite will cross the placenta depends heavily on when during pregnancy the infection happens. A large Norwegian study tracking nearly 36,000 pregnant women found that the overall transmission rate was 23%, but it varied dramatically by trimester: about 13% in the first trimester, 29% in the second, and 50% in the third.
This creates an unfortunate tradeoff. Infections earlier in pregnancy are less likely to reach the baby, but when they do, the damage tends to be far more severe because the brain and organs are still forming. Infections later in pregnancy cross the placenta more easily, but the baby is further along in development and the effects are often milder. The second trimester falls somewhere in between on both counts.
Not All Cats Carry the Same Risk
Your indoor cat who has never caught a mouse and eats commercial kibble is a very different risk profile than a barn cat that hunts daily. Cats pick up Toxoplasma by eating infected animals or raw meat. Research from a veterinary teaching hospital in Germany found that outdoor cats were about 2.4 times more likely to test positive for Toxoplasma antibodies than indoor-only cats. Among cats that tested positive, 44% were outdoor cats compared to 56% indoor cats, even though indoor cats made up a much larger share of the study population.
Diet plays a role too. Cats fed raw meat-based diets have higher exposure risk than those eating commercial dry food. If your cat lives entirely indoors and eats only processed cat food, the chance it’s shedding Toxoplasma oocysts is low. It’s not zero, since a mouse could find its way inside, but it’s considerably lower than for a cat with outdoor access.
There’s another reassuring fact: cats typically only shed oocysts for 10 to 14 days after their first infection. After that initial shedding period, most cats develop immunity and don’t shed again. So even if your cat was exposed years ago, it’s unlikely to be actively shedding now.
How Infection Is Detected
If there’s concern about exposure, a blood test can clarify the picture. The test looks for two types of antibodies. One type (IgM) signals a current or very recent infection. The other (IgG) indicates a past infection. If only IgG shows up with no IgM, the infection likely happened 6 to 12 months earlier or more, meaning the immune system has already dealt with it. If both are detected, additional testing helps pin down the timing, which is critical for deciding next steps.
A woman who was infected before becoming pregnant generally has immunity that protects the baby. The concern is a new, first-time infection happening during the pregnancy itself.
Treatment If Infection Occurs
If a pregnant woman does test positive for a new infection, treatment can significantly reduce the risk of the parasite reaching the baby. When treated with antiparasitic medications, the rate of vertical transmission drops to roughly 10%. Treatment protocols shift as pregnancy progresses. In the first trimester, doctors typically use a medication that concentrates in the placenta and acts as a barrier. After about 18 weeks, or if fetal infection is confirmed, a different combination of drugs is used that can cross the placenta and treat the baby directly.
Early detection gives more treatment options and better outcomes, which is why some countries include routine Toxoplasma screening in prenatal care. In the United States, screening isn’t universal, but your provider can order the blood test if you have risk factors or concerns.
Practical Steps to Stay Safe
You don’t need to rehome your cat. The CDC’s guidelines focus on breaking the transmission chain, and they’re straightforward:
- Have someone else scoop the litter box. If that’s not possible, wear disposable gloves and wash your hands thoroughly with soap and water afterward.
- Scoop daily. Because oocysts need at least 24 hours to become infectious, cleaning the box every day removes them before they pose a threat.
- Wear gloves when gardening. Outdoor soil and sandboxes can harbor oocysts from neighborhood cats. Wash your hands after any contact with soil or sand.
- Cover outdoor sandboxes to keep cats from using them.
- Keep your cat indoors during your pregnancy if possible, and feed it commercial cat food rather than raw meat.
It’s also worth noting that cat feces aren’t the only source of Toxoplasma. Undercooked meat (especially lamb, pork, and venison) and unwashed produce are actually more common routes of infection in many countries. Cooking meat to safe internal temperatures and washing fruits and vegetables thoroughly are equally important precautions during pregnancy.