Most first-trimester miscarriages are caused by chromosomal abnormalities in the embryo, accounting for 50% or more of all early pregnancy losses. That means many miscarriages happen because of random genetic errors during fertilization, and no amount of rest or lifestyle change could have prevented them. But that doesn’t mean you’re powerless. A meaningful portion of miscarriage risk comes from factors you can influence, including underlying health conditions, nutrition, weight, and environmental exposures.
Why Most Early Miscarriages Can’t Be Prevented
When an embryo receives the wrong number of chromosomes during fertilization, it usually cannot develop normally. The pregnancy ends on its own, typically before 12 weeks. This is the single most common reason for first-trimester loss, and it occurs randomly regardless of what the mother does or doesn’t do. It becomes more likely with age: women between 20 and 30 have roughly a 9% to 17% chance of miscarriage, while at 35 the risk rises to about 20%, at 40 it’s around 40%, and by 45 it reaches 80%.
Understanding this matters because guilt after a miscarriage is nearly universal, and usually misplaced. The steps below genuinely reduce risk from the causes that are modifiable, but they can’t override a chromosomal problem. If you’ve experienced a loss despite doing everything right, that’s the most likely explanation.
Start Folic Acid Before Conception
The U.S. Preventive Services Task Force recommends that anyone planning to or who could become pregnant take 400 to 800 micrograms of folic acid daily. To get the full benefit, start at least one month before you try to conceive and continue through the first two to three months of pregnancy. Folic acid is best known for preventing neural tube defects, but adequate folate status also supports the rapid cell division happening in very early pregnancy. Most prenatal vitamins contain this amount, so if you’re already taking one, you’re likely covered.
Manage Your Weight Before Pregnancy
Entering pregnancy at a higher weight increases the odds of early loss. A large study tracking nearly 15,000 pregnancies found that women with obesity had a 36% higher risk of miscarriage before 12 weeks compared to women at a normal weight. For every single-point increase in BMI, the risk of early miscarriage rose by about 3%. Being underweight, on the other hand, did not appear to raise miscarriage risk in the same analysis.
If your BMI is in the overweight or obese range, even modest weight loss before conception can shift the odds. This isn’t about reaching a perfect number. Losing 5% to 10% of body weight improves hormonal balance and metabolic health in ways that support early pregnancy.
Get Your Thyroid Checked
Thyroid problems are one of the most overlooked and most treatable causes of pregnancy loss. During the first trimester, your TSH level (the hormone that reflects thyroid function) should ideally stay between 0.2 and 2.5. Women whose TSH runs between 4.5 and 10 have nearly twice the risk of miscarriage, and those above 10 face almost four times the risk compared to women in the normal range.
The reassuring part: levels between 2.5 and 4.5 don’t appear to increase miscarriage risk significantly. If you have a known thyroid condition, or if you’ve had an unexplained miscarriage, ask for a thyroid panel early in pregnancy or while planning to conceive. Treatment with thyroid medication is straightforward and can make a real difference.
Keep Caffeine Under 200 Milligrams a Day
Caffeine crosses the placenta, and the embryo can’t metabolize it efficiently. Research reviewed by the American College of Obstetricians and Gynecologists found that consuming 200 milligrams or more per day was associated with roughly double the risk of miscarriage. Below that threshold, caffeine did not appear to be a major contributing factor.
To put that in practical terms: a standard 8-ounce cup of brewed coffee contains about 95 milligrams of caffeine, so two cups a day puts you right at the limit. A shot of espresso has around 63 milligrams. Tea ranges from 25 to 50 milligrams per cup. If you’re a heavy coffee drinker, tapering down before conception gives you time to adjust without the headaches of going cold turkey while newly pregnant.
Exercise Safely, Don’t Stop Entirely
There’s a persistent myth that exercise in the first trimester causes miscarriage. It doesn’t. Current guidelines recommend that pregnant women get at least 150 minutes of moderate-intensity aerobic activity per week. Moderate intensity means you can talk normally but can’t sing: think brisk walking, swimming, or light gardening.
The caveats are practical. Avoid becoming overheated, especially in the first trimester, since elevated core body temperature can affect early development. Skip activities with jerky, bouncy, or high-impact motions that increase the risk of falls or abdominal trauma. Contact sports, hot yoga, and scuba diving fall into the “avoid” category. But regular movement improves circulation, helps manage weight, reduces stress, and supports the kind of metabolic health that protects early pregnancy.
Reduce Exposure to Phthalates
Phthalates are chemicals used to soften plastics and add fragrance to personal care products. Research from Harvard found that women with the highest concentrations of a specific phthalate called DEHP were 60% more likely to lose a pregnancy before 20 weeks than those with the lowest levels. DEHP is found in PVC plastics, vinyl building materials, shower curtains, plastic blinds, and some food packaging. Because it bonds loosely to plastic, it leaches easily into air, water, and food.
You can’t eliminate phthalate exposure entirely, but you can reduce it. Choose personal care products labeled “fragrance free” or “phthalate-free” rather than ones listing “fragrance” or “parfum” as an ingredient, since synthetic fragrances are a common source. Avoid heating food in plastic containers. When possible, choose glass or stainless steel for food storage. These steps matter most in the weeks surrounding conception and early pregnancy, when the embryo is most vulnerable.
Progesterone for Women With Prior Losses
If you’ve had one or more previous miscarriages and experience vaginal bleeding in a new pregnancy, progesterone supplementation may improve your chances of carrying to term. Clinical evidence shows that vaginal progesterone, taken twice daily, increases live birth rates in this specific group. The benefit is strongest for women who’ve had three or more prior losses and are currently bleeding, but it also appears to help women with just one or two previous miscarriages.
Progesterone supports the uterine lining and helps maintain early pregnancy. It’s not something to take on your own; it requires a prescription and monitoring. But if you have a history of loss and notice spotting or bleeding, it’s worth bringing up immediately with your provider rather than waiting for a scheduled appointment.
Low-Dose Aspirin After Previous Miscarriage
A large NIH trial of more than 1,000 women between 18 and 40 who had experienced one or two prior miscarriages found that taking 81 milligrams of aspirin daily before conception and through pregnancy improved the odds of both getting pregnant and delivering a live baby. The benefit was most consistent in women who took aspirin at least four days per week starting before they conceived.
Low-dose aspirin is also a standard part of treatment for antiphospholipid syndrome, an immune condition that causes blood clots in the placenta and is a well-established cause of recurrent miscarriage. If you’ve had multiple losses, testing for this condition is a reasonable step. For women without a specific diagnosis but with a history of one or two losses, the aspirin evidence is encouraging, though it’s a conversation to have with your provider about your individual situation.
Alcohol, Smoking, and Recreational Drugs
There is no known safe amount of alcohol during pregnancy. Alcohol exposure in the first trimester, when organ systems are forming, is associated with both miscarriage and developmental harm. Smoking increases miscarriage risk through multiple pathways: it restricts blood flow to the uterus, introduces carbon monoxide into the bloodstream, and damages egg quality. Recreational drugs, including marijuana, carry similar vascular risks. If you’re planning a pregnancy, quitting all three before conception gives you the cleanest start, and quitting at any point still reduces risk going forward.
Stress, Sleep, and Infections
Chronic, severe stress raises levels of the hormone cortisol, which can interfere with progesterone production and implantation. This doesn’t mean ordinary daily stress causes miscarriage. It means prolonged, unmanaged stress with poor sleep and no recovery time can contribute to an environment that’s less supportive of early pregnancy. Prioritizing seven to nine hours of sleep per night and finding even basic stress management tools, whether that’s walking, breathing exercises, or cutting back commitments, has physiological benefits beyond just feeling better.
Certain infections also raise first-trimester risk. Listeria (from unpasteurized dairy, deli meats, and raw sprouts), toxoplasmosis (from undercooked meat or cat litter), and untreated urinary tract or vaginal infections can all threaten early pregnancy. Standard food safety precautions and prompt treatment of any infection reduce these risks substantially.