Most early miscarriages are caused by chromosomal abnormalities in the embryo that no action can prevent. More than half of losses before 12 weeks fall into this category. That’s a hard truth, but it’s also a relieving one: if you do experience an early loss, it almost certainly wasn’t something you did wrong. Still, there are real, evidence-backed steps that reduce the risks you can control.
At weeks 3 through 5, many people don’t even know they’re pregnant yet, which makes the risk at that stage hard to measure. By week 6, the miscarriage rate drops to about 9.4%, and by week 7 it falls to 4.2%. At week 8, it’s roughly 1.5% and continues to decline. The first month is the highest-risk window, and it’s also the period where your earliest habits and health conditions matter most.
What You Can Actually Control
Since chromosomal problems cause the majority of early losses, the preventable factors involve your own health, environment, and exposures. These fall into a few categories: managing pre-existing conditions, avoiding harmful substances and infections, staying physically safe, and getting the right nutrients. None of these guarantee a healthy pregnancy, but together they meaningfully shift the odds in your favor.
Check Your Thyroid Before or Early in Pregnancy
An underactive thyroid is one of the most common treatable risk factors for early miscarriage, and many people don’t know they have one. The Endocrine Society recommends keeping thyroid-stimulating hormone (TSH) levels between 0.2 and 2.5 mU/L during the first trimester. Women with TSH levels between 4.5 and 10 have 1.8 times the miscarriage risk compared to women in the normal range. Above 10, the risk nearly quadruples.
The good news: TSH between 2.5 and 4.5 doesn’t appear to raise miscarriage risk, so you don’t need to hit a perfect number. If you’re planning a pregnancy or just got a positive test, ask for a thyroid panel. Treatment with thyroid hormone replacement is straightforward and can make a significant difference.
Caffeine: Lower Than You Think
Major health organizations, including ACOG, the NHS, and the European Food Safety Authority, recommend capping caffeine at 200 mg per day during pregnancy. That’s roughly one 12-ounce cup of brewed coffee. But recent research is raising questions about whether even that limit is fully safe. Some studies have found associations between caffeine intake below 200 mg and pregnancy loss.
You don’t need to quit caffeine entirely, but keeping intake well under 200 mg is a reasonable precaution in the first month. Watch for hidden sources: tea, chocolate, energy drinks, and some medications all contain caffeine that adds up.
Avoid Overheating Your Body
Hot tubs, saunas, and very hot baths pose a real risk in the first trimester. Water temperatures at or above 101°F (38.3°C) have been linked to increased risk of neural tube defects, and the spine is fully formed just six weeks after your last missed period, so the window of vulnerability is narrow and early.
If you want to eliminate the risk entirely, skip the hot tub through the first trimester. If you do use one, keep sessions short, stay away from the jets where water is hottest, and make sure the temperature stays below 101°F. This same logic applies to exercise: ACOG specifically recommends avoiding overheating in the first trimester. Moderate-intensity activity is fine (you can talk normally but can’t sing), but don’t push to the point of heavy overheating.
Exercise Is Safe, With One Caveat
Exercise does not cause miscarriage. If you were active before pregnancy, you can generally continue the same workouts. ACOG’s guidance is simple: moderate intensity is the sweet spot. The one caution is overheating, especially in the first trimester. Stay hydrated, avoid exercising in extreme heat, and listen to your body. There’s no specific heart rate cutoff you need to worry about.
Protect Yourself From Infections
Certain infections can directly trigger early pregnancy loss. Rubella (German measles) in the first four months of pregnancy can cause miscarriage and serious birth defects. If you’re not sure whether you’re immune, a blood test can check, and vaccination before conception provides protection (you can’t get the vaccine while pregnant).
Listeria, found in unpasteurized dairy, deli meats, and some ready-to-eat foods, is another well-known risk. Basic food safety steps matter more now than usual: cook meats thoroughly, wash produce, avoid soft cheeses made with unpasteurized milk, and skip raw or undercooked seafood. These precautions are especially important in the first month when the pregnancy is most vulnerable.
Progesterone and Aspirin: Who They Help
If you’ve had previous miscarriages, two medical interventions have evidence behind them, but they’re targeted, not universal.
Progesterone supplementation has shown benefit specifically for women who have had at least one prior miscarriage and are experiencing bleeding in a current pregnancy. ACOG guidelines also suggest that women with three or more previous losses may benefit from progesterone therapy in the first trimester. For someone with no history of loss, there’s no strong evidence that progesterone supplementation prevents miscarriage.
Low-dose aspirin (81 mg daily) was studied in the NIH’s EAGeR trial, which included over 1,000 women with one or two prior miscarriages. Researchers found that taking low-dose aspirin at least four days per week improved the chances of both getting pregnant and delivering a live baby. The women in the trial started aspirin while trying to conceive and continued through week 36. This isn’t a blanket recommendation for all pregnancies, but it’s worth discussing with your provider if you have a history of loss.
Prenatal Vitamins and Folic Acid
Folic acid is the most important supplement to start before or immediately after conception. Its primary role is preventing neural tube defects, and the critical window for that protection is the first few weeks of pregnancy, often before you know you’re pregnant. Most prenatal vitamins contain the recommended 400 to 800 micrograms. Starting a prenatal vitamin as soon as you’re trying to conceive, rather than waiting for a positive test, gives you the best coverage during the first month.
Alcohol, Smoking, and Drug Use
There is no known safe level of alcohol during pregnancy, and drinking in the first month increases miscarriage risk. Smoking raises the risk as well, both through direct toxic effects on the embryo and by reducing blood flow to the uterus. Recreational drug use, including marijuana, is similarly linked to higher rates of early loss. If you’re trying to conceive, stopping these exposures before conception gives you the cleanest start.
What You Can’t Prevent
Even with every precaution in place, some pregnancies will end in early loss. Roughly 80% of all miscarriages happen in the first 12 weeks, and the majority are caused by random genetic errors during cell division. These errors aren’t inherited, aren’t caused by anything the mother did, and typically don’t repeat in future pregnancies. If you experience a first-trimester loss, it reflects the biology of early human development, not a personal failure.