About 15% of recognized pregnancies end in miscarriage, and the vast majority of those losses happen in the first trimester. While many miscarriages result from chromosomal problems that nothing can prevent, there are specific exposures, foods, and habits that research links to higher risk. Knowing what to avoid gives you real control over the factors you can influence.
Pain Relievers That Raise the Risk
Over-the-counter anti-inflammatory painkillers like ibuprofen and naproxen are among the most significant avoidable risks in early pregnancy. A population-based study published in the BMJ found that using these medications during pregnancy increased miscarriage risk by 80%. The timing and duration mattered enormously: taking them around the time of conception was associated with a more than fivefold increase in risk, and using them for longer than a week raised the risk eightfold.
If you need pain relief in early pregnancy, acetaminophen (Tylenol) is generally considered the safer alternative. Aspirin was also linked to increased miscarriage risk in the same study, so it’s worth checking the labels of any pain or cold medications you have on hand, since many combination products contain these ingredients.
Caffeine: Where the Line Is
You don’t need to give up coffee entirely. The American College of Obstetricians and Gynecologists sets the threshold at 200 milligrams per day, roughly the amount in one 12-ounce cup of brewed coffee. Below that level, caffeine does not appear to be a major contributing factor in miscarriage. Above it, the evidence is less clear, but the risk trends upward. Keep in mind that caffeine also shows up in tea, soft drinks, chocolate, and energy drinks, so the total adds up faster than you might expect.
Alcohol Has No Known Safe Amount
A large meta-analysis combining data from multiple studies found that for women drinking five or fewer drinks per week, each additional drink per week was associated with a 6% increase in miscarriage risk. That percentage compounds quickly. Because researchers have not identified a threshold below which alcohol is clearly safe for a developing pregnancy, the standard guidance is to avoid it entirely once you know you’re pregnant or are actively trying to conceive.
Foods That Carry Listeria Risk
Listeria is a type of bacteria that can cross the placenta and reach the fetus directly, potentially causing miscarriage, premature birth, or serious infection. Pregnant women are roughly 10 times more susceptible to listeriosis than the general population, making food safety a genuinely important concern rather than an overreaction.
The highest-risk foods include:
- Soft and unpasteurized cheeses such as brie, camembert, queso fresco, and feta made from raw milk. One study found that eating unpasteurized dairy products was reported by 68.5% of listeriosis cases compared to less than 1% of controls.
- Deli meats and processed meats unless heated until steaming. Uncooked hot dogs carried a 12-fold increased risk in one study. Pâté, smoked meats, and smoked seafood also pose risk.
- Pre-prepared salads and deli counter foods including pre-packaged coleslaw, hummus from commercial establishments, and ready-to-eat vegetables bought pre-cut.
The common thread is foods that sit at refrigerator temperatures for extended periods without being cooked before eating. Listeria, unlike most bacteria, can grow in cold environments. Heating food thoroughly kills it.
High-Mercury Fish
Mercury in fish accumulates as methylmercury, which is harmful to fetal neurological development. The FDA and EPA specifically name seven fish to avoid during pregnancy: shark, swordfish, king mackerel, tilefish from the Gulf of Mexico, orange roughy, marlin, and bigeye tuna. These large, long-lived predatory fish accumulate the highest mercury levels.
Lower-mercury options like salmon, sardines, tilapia, and shrimp are not only safe but beneficial. The goal is to choose fish wisely rather than avoid it altogether.
Heat Exposure in Hot Tubs and Saunas
Raising your core body temperature above 38.9°C (about 102°F) during the first trimester has been linked to developmental problems and pregnancy loss. Research testing how quickly women reach that threshold found that in a hot tub set to 41°C (106°F), none of the participants hit the danger zone before 10 minutes, and in a cooler 39°C tub, it took at least 15 minutes. Many women felt too uncomfortable to stay that long and left while their temperatures were still below the threshold.
This means a brief soak is unlikely to cause harm, but prolonged sessions carry real risk. The safest approach in the first trimester is to limit hot tub time to under 10 minutes or avoid them entirely. Saunas follow a similar principle: in the study, none of the women were able to stay in a sauna long enough for their temperature to reach dangerous levels, though erring on the side of caution is reasonable. Warm baths at normal temperatures are fine.
Cat Litter and Soil
Toxoplasmosis is a parasitic infection that can cause miscarriage and is spread through contact with infected cat feces. The parasite can live in cat litter and in garden soil where cats have been. If you have a cat, have someone else handle litter box duties during your pregnancy. If that’s not possible, wear gloves and wash your hands thoroughly afterward. The same applies to gardening: wear gloves any time you’re working in soil, and wash produce from your garden well before eating it.
Environmental Chemicals
Certain chemicals found in everyday plastics and household products act as endocrine disruptors, meaning they interfere with hormone signaling. Research on bisphenols and phthalates, chemicals common in plastic food containers, receipt paper, and personal care products, has found that preconception and early pregnancy exposure to some phthalate metabolites is associated with higher odds of miscarriage. The science on which specific chemicals matter most is still being refined, but practical steps to reduce exposure include avoiding microwaving food in plastic containers, choosing fragrance-free personal care products, and storing food in glass or stainless steel when possible.
Smoking and Secondhand Smoke
Smoking restricts blood flow to the placenta and exposes the embryo to hundreds of toxic compounds. It is one of the most well-established modifiable risk factors for miscarriage. Secondhand smoke exposure carries similar, though smaller, risks. If you smoke, the first trimester is the most critical window to stop, and if people in your household smoke, having them do so outside makes a measurable difference.
What You Don’t Need to Avoid
Some of the most common fears about early pregnancy are not well supported by evidence. Exercise, including running, jogging, and racquet sports, is safe to continue if you were doing it before pregnancy. ACOG encourages experienced athletes to maintain their routines, with adjustments as needed. The old advice about keeping your heart rate below 140 beats per minute was retired years ago.
Sex is also safe in a normal pregnancy and does not cause miscarriage. Neither does moderate stress, working at a computer, or flying on an airplane. The things that actually matter are more specific than most people realize, which is why focusing on the evidence-based list above is more useful than trying to restrict every aspect of daily life.