The first trimester is when your baby’s major organs, brain, and spinal cord begin forming, which makes the first 12 weeks a window where certain foods, chemicals, medications, and habits carry outsized risk. Here’s what to steer clear of and why it matters most right now.
Foods That Carry Infection Risk
Pregnant women are 10 times more likely than the general population to get a Listeria infection, a type of food poisoning that can cause miscarriage or stillbirth even when you feel only mildly ill. The bacteria thrive in refrigerated, ready-to-eat foods, so the biggest risks come from things you eat without heating first.
The CDC flags these as higher-risk choices during pregnancy:
- Deli meats and hot dogs that haven’t been reheated until steaming (165°F)
- Refrigerated pâté or meat spreads
- Premade deli salads like coleslaw, potato salad, tuna salad, chicken salad, and egg salad
- Soft cheeses made from unpasteurized milk such as brie, camembert, blue-veined cheese, and queso fresco
- Any queso fresco-style cheese, even when made with pasteurized milk, including queso blanco and requesón
- Cheese sliced at a deli counter that you eat without heating
The common thread is that cooking or thorough reheating kills Listeria. A cold turkey sandwich from the deli is risky; the same sandwich heated until the meat is steaming is not.
High-Mercury Fish
Fish is actually encouraged during pregnancy for its omega-3 fatty acids, but a handful of species accumulate enough mercury to harm a developing nervous system. The FDA advises completely avoiding these seven types:
- King mackerel
- Marlin
- Orange roughy
- Shark
- Swordfish
- Tilefish from the Gulf of Mexico
- Bigeye tuna
Lower-mercury options like salmon, shrimp, tilapia, and canned light tuna are safe at 8 to 12 ounces per week, roughly two to three palm-sized servings. That’s the FDA’s recommended range specifically for pregnant women.
Alcohol
There is no known safe amount of alcohol during pregnancy, and no safe trimester to drink. But the first trimester carries a specific risk: alcohol exposure in the first three months can cause abnormal facial features associated with fetal alcohol spectrum disorders. Brain development continues throughout the entire pregnancy, so central nervous system damage and behavioral problems can result from drinking at any point. The CDC’s position is straightforward: skip it entirely.
Caffeine Limits
You don’t have to give up coffee, but you do need to watch the total. The American College of Obstetricians and Gynecologists considers less than 200 mg of caffeine per day moderate, and at that level it does not appear to be a major contributor to miscarriage or preterm birth. That works out to roughly one 12-ounce cup of brewed coffee.
Keep in mind that caffeine adds up from multiple sources: tea, chocolate, sodas, energy drinks, and some over-the-counter pain relievers. If you’re drinking a large coffee plus an afternoon tea, you may be above 200 mg without realizing it.
Common Medications to Stop
Over-the-counter painkillers like ibuprofen and naproxen are so routine that many people take them without a second thought, but their safety in the first trimester is not established. ACOG’s guidance is that pregnant women should not take these unless specifically told to by their provider. Acetaminophen (Tylenol) is generally considered the safer alternative for pain and fever during pregnancy, though you should still use the lowest effective dose.
Prescription acne medications pose a more severe risk. Isotretinoin (sometimes sold as Accutane or its generic equivalents) is one of the most well-documented causes of birth defects in modern medicine. The American Academy of Dermatology lists it alongside tazarotene and spironolactone as medications to stop immediately if you become pregnant, because all three can cause serious birth defects.
Skincare Ingredients
Retinoids are the ingredient family to watch. Tretinoin (Retin-A) and adapalene (Differin), both popular for acne and anti-aging, are topical forms of vitamin A that most dermatologists recommend stopping during pregnancy. The concern connects to a broader issue: consuming more than 10,000 IU of preformed vitamin A (retinol) daily during pregnancy has been linked to birth defects of the head, heart, brain, and spinal cord in a study of over 22,000 women. Topical retinoids deliver a much smaller dose than oral supplements, but experts still advise against them as a precaution during the first trimester when organ formation is most active.
Salicylic acid, found in many drugstore acne washes, is generally considered safe for limited use, but it’s worth running by your provider before continuing a daily routine with it. Azelaic acid is thought to be safe during pregnancy and is often the go-to swap for retinoid-based products.
Excess Vitamin A Supplements
Prenatal vitamins are formulated to stay within safe limits, but if you’re taking additional supplements, check the label for retinol or preformed vitamin A. Beta-carotene, the plant-based form of vitamin A found in carrots and sweet potatoes, does not carry the same risk because your body only converts what it needs. The concern is specifically with preformed vitamin A from animal sources or supplements. Staying under 10,000 IU daily from all sources is the threshold most commonly cited.
Hot Tubs, Saunas, and Excessive Heat
Raising your core body temperature in the first trimester is linked to neural tube defects like spina bifida and anencephaly, conditions where the brain or spinal cord doesn’t form properly. Hot tubs, saunas, steam rooms, and hot yoga all carry this risk. The neural tube closes within the first 28 days of pregnancy, often before you even know you’re pregnant, which is why heat exposure is particularly concerning in the earliest weeks.
This doesn’t mean warm baths are off limits. The issue is sustained exposure to water or air hot enough to raise your core temperature significantly. A bath where the water cools as you sit in it is very different from a hot tub that maintains 104°F. When in doubt, if your skin is turning red and you’re sweating, step out.
Smoking and Secondhand Smoke
Smoking during the first trimester restricts blood flow to the placenta and reduces the oxygen reaching your developing baby. It raises the risk of miscarriage, ectopic pregnancy, and placental problems later on. Secondhand smoke carries similar, though smaller, risks. If you smoke, the first trimester is the most impactful time to stop, because the baby’s circulatory and respiratory systems are just starting to form.
Cat Litter and Raw Soil
Toxoplasmosis is a parasitic infection spread through cat feces and contaminated soil. In most healthy adults it causes no symptoms, but during the first trimester it can cause miscarriage or serious developmental problems. If you have cats, have someone else handle litter box duty. If you garden, wear gloves and wash your hands thoroughly afterward. Indoor cats that don’t hunt are lower risk, but the precaution is easy enough that it’s worth taking regardless.