The first trimester is when your baby’s major organs, brain, and spinal cord begin forming, making it the most sensitive window for exposure to harmful substances. What you eat, drink, apply to your skin, and encounter in your environment all matter more during these first 12 weeks than at almost any other point in pregnancy. Here’s a clear breakdown of what to steer clear of and why.
Alcohol
No amount of alcohol has been established as safe during the first trimester. This is the period of organogenesis, when the brain, heart, and other organs are taking shape, and alcohol can directly interfere with that process. Even moderate drinking during early pregnancy is linked to a higher risk of miscarriage. Binge drinking (five or more drinks on a single occasion) during the first trimester is associated with an increased risk of oral and facial clefts in infants.
Alcohol exposure during the weeks surrounding conception and early pregnancy also raises the risk of neural tube defects, which affect the brain and spinal cord. Women who drank more than once a week during this period had roughly double the risk compared to non-drinkers. The safest approach is to stop drinking as soon as you know you’re pregnant, or ideally when you start trying to conceive.
High-Mercury Fish
Fish is a valuable source of protein and omega-3 fatty acids during pregnancy, but certain species accumulate dangerously high levels of mercury, which can harm a developing nervous system. The FDA lists seven types of fish to avoid entirely:
- King mackerel
- Marlin
- Orange roughy
- Shark
- Swordfish
- Tilefish (from the Gulf of Mexico)
- Bigeye tuna
You don’t need to avoid fish altogether. The FDA recommends eating two to three 4-ounce servings per week of lower-mercury options like salmon, shrimp, tilapia, and pollock. Canned light tuna is generally lower in mercury than bigeye or albacore.
Foods That Carry Infection Risk
Pregnancy suppresses parts of your immune system, making you significantly more vulnerable to foodborne infections like listeriosis and toxoplasmosis. Listeria is especially dangerous because it can cross the placenta and cause miscarriage, stillbirth, or serious infection in the baby. The FDA recommends avoiding these foods unless they’ve been thoroughly cooked or heated:
- Deli meats, hot dogs, and luncheon meats unless reheated until steaming hot
- Unpasteurized milk and any foods made with it
- Soft cheeses like queso fresco, queso blanco, and requesón (even versions made from pasteurized milk carry higher risk for these specific cheese types)
- Refrigerated smoked seafood such as lox, kippered salmon, or smoked trout, unless cooked into a dish like a casserole
- Refrigerated pâtés and meat spreads
- Raw or undercooked meat, poultry, and eggs
- Unwashed raw fruits and vegetables
The key distinction is temperature. Listeria can grow even in refrigerated foods, which is why deli meats and smoked fish are risky despite being “cooked.” Heating them to steaming (about 165°F) kills the bacteria.
Caffeine Over 200 Milligrams Per Day
You don’t have to give up coffee entirely. The American College of Obstetricians and Gynecologists considers moderate caffeine intake, defined as less than 200 milligrams per day, unlikely to be a major factor in miscarriage or preterm birth. That’s roughly one 12-ounce cup of brewed coffee.
Keep in mind that caffeine shows up in more than just coffee. A cup of black tea has about 50 mg, a can of cola around 35 mg, and a shot of espresso roughly 63 mg. Dark chocolate contains small amounts too. If you’re combining sources throughout the day, they add up.
Common Pain Relievers (NSAIDs)
Ibuprofen (Advil, Motrin), naproxen (Aleve), and aspirin are among the most commonly used medications during early pregnancy, often before people realize they’re pregnant. These anti-inflammatory painkillers can interfere with implantation and early development. Ibuprofen alone is used by roughly 1 in 4 women during the first trimester, making it one of the most frequent exposures.
Acetaminophen (Tylenol) is generally considered the safer alternative for pain and fever during pregnancy, though using it only when truly needed and at the lowest effective dose is a reasonable approach. If you take any prescription medications, talk to your provider before stopping or switching, since abruptly discontinuing some drugs carries its own risks.
Retinoids and Certain Skincare Ingredients
Retinoids are vitamin A derivatives found in many anti-aging and acne products. The oral form (isotretinoin, commonly known by the former brand name Accutane) is one of the most well-established causes of birth defects and is absolutely off-limits during pregnancy. Topical retinoids like tretinoin and retinol absorb far less into the bloodstream, but there are published case reports of birth defects consistent with retinoid damage, so the current guidance is to stop using them once you’re pregnant or trying to conceive.
Hydroquinone, a skin-lightening ingredient used for dark spots and melasma, absorbs into the body at substantially higher rates than most topical products. It’s best avoided until after pregnancy. Most other common skincare ingredients, including gentle cleansers, moisturizers, and sunscreens, are not expected to pose a risk because they stay local and don’t reach significant levels in the blood.
Hot Tubs and Saunas
Raising your core body temperature above about 101°F (38.9°C) during early pregnancy has been linked to an increased risk of neural tube defects. Research on hot tub exposure found that women in a 106°F tub reached that danger threshold within 10 minutes. In a cooler 102°F tub, it took about 15 minutes. Saunas raised body temperature more slowly, and none of the study participants reached the higher threshold of 103°F before needing to get out due to discomfort.
The practical takeaway: brief dips of under 10 minutes in a hot tub are lower risk, but it’s safest to avoid prolonged soaking entirely during the first trimester. Warm baths at a comfortable temperature are fine since the water cools and your upper body stays exposed to air.
Cat Litter and Garden Soil
Toxoplasmosis is a parasitic infection that can cause serious harm to a developing baby, including brain and eye damage. Cats that go outdoors can carry the parasite in their feces, and it becomes infectious one to five days after being shed. The FDA recommends having someone else handle litter box duties if possible. If you must do it yourself, wear disposable gloves, wash your hands thoroughly afterward, and change the litter daily so the parasite doesn’t have time to become infectious.
The same parasite lives in garden soil and sandboxes where outdoor cats may have been. Wear gloves while gardening, keep outdoor sandboxes covered, and wash your hands well after handling soil. Raw or undercooked meat is actually a more common source of toxoplasmosis infection than cat litter, which is another reason to cook all meat thoroughly.
Chemical Exposures at Home and Work
Certain industrial and household chemicals can cross the placenta and affect fetal development. Phthalates, found in some plastics, fragrances, and personal care products, have been detected in the urine of over 90% of pregnant women tested and are associated with preterm delivery and disrupted hormone function. Flame retardants, commonly found in furniture foam and electronics, have been linked to thyroid disruption and altered brain development in children who were exposed in the womb.
Perfluorinated compounds (the “forever chemicals” in nonstick cookware and water-resistant fabrics) are detectable in the blood of nearly all pregnant women and are associated with reduced fetal growth. Organic solvents, lead, and pesticides also carry documented risks. If your job involves regular contact with paints, solvents, heavy metals, or industrial cleaning agents, talk to your employer about reassignment or protective measures during the first trimester.
At home, practical steps include ventilating rooms when using cleaning products, choosing fragrance-free personal care products when possible, avoiding heating food in plastic containers, and running cold water for a few seconds before filling a glass if you have older plumbing that may contain lead.
Contact Sports and High-Impact Activities
Current guidelines recommend avoiding sports and activities with a risk of abdominal contact or falling. This includes football, rugby, martial arts, horseback riding, downhill skiing, and gymnastics. The concern is blunt trauma to the uterus, which can cause placental separation even in early pregnancy. Moderate exercise like walking, swimming, stationary cycling, and prenatal yoga is not only safe but actively beneficial throughout the first trimester. Staying active helps manage nausea, fatigue, and mood changes during these early weeks.