Most missed miscarriages cannot be prevented. Roughly two-thirds of all miscarriages are caused by random chromosomal errors in the embryo, events that happen at or near conception and are entirely outside anyone’s control. A missed miscarriage, where the embryo stops developing but the body doesn’t recognize the loss right away, follows the same pattern. That said, a meaningful fraction of pregnancy losses are tied to treatable health conditions, hormonal imbalances, and environmental exposures. Understanding what you can and can’t influence is the most honest starting point.
Why Most Missed Miscarriages Are Unavoidable
A missed miscarriage is diagnosed when an ultrasound shows a pregnancy that has stopped growing but hasn’t been expelled from the uterus. You may still feel pregnant because hormone levels haven’t dropped yet, and there’s no bleeding or cramping to signal something is wrong. Doctors confirm the diagnosis when an embryo measuring 7 mm or larger has no detectable heartbeat, or when a gestational sac reaches 25 mm with no visible embryo inside.
The most common cause is the same as for any first-trimester loss: the embryo received the wrong number of chromosomes during fertilization. A large study of over 7,000 miscarriage cases found chromosomal abnormalities in 67% of them. These errors are spontaneous. They don’t reflect a genetic problem in either parent, and they can’t be predicted or corrected after conception. This is why doctors emphasize that miscarriage is not something you caused by exercising, working, having sex, or feeling stressed.
Factors That Raise Your Risk
Age is the single biggest variable. Miscarriage risk sits between 9% and 17% for people in their twenties, rises to about 20% at age 35, doubles to 40% at age 40, and reaches 80% by age 45. The increase is driven almost entirely by the higher rate of chromosomal errors in eggs as they age. This doesn’t mean pregnancy after 35 is inadvisable, but it does explain why losses become more common.
Certain medical conditions also raise risk in ways that are, importantly, treatable:
- Thyroid disorders. An underactive thyroid is linked to higher miscarriage rates. Women with thyroid-stimulating hormone (TSH) levels above 4.5 in the first trimester had nearly double the odds of miscarriage compared to those in the normal range. When TSH climbed above 10, the risk was almost four times higher. Many people with thyroid problems don’t know their levels are off until they’re tested.
- Blood clotting conditions. Antiphospholipid syndrome and other clotting disorders can interfere with blood flow to the placenta. In one study, women with antiphospholipid antibodies who received no treatment had a 54% miscarriage rate, compared to about 20% in those who were treated.
- Uncontrolled diabetes. Poorly managed blood sugar in early pregnancy significantly raises miscarriage risk. Well-controlled diabetes does not carry the same level of risk.
- Uterine abnormalities. Structural issues like a uterine septum or large fibroids can prevent an embryo from implanting properly or growing normally.
What You Can Actually Do Before Pregnancy
The most effective window for reducing risk is before conception. If you’re planning a pregnancy, getting a full picture of your health beforehand gives you the best chance of catching problems that are fixable.
Ask for thyroid screening, especially if you have a family history of thyroid disease, have had a previous miscarriage, or are on thyroid medication. The recommended TSH target in the first trimester is below 2.5. Nearly half of women already taking thyroid medication have levels above this threshold, which means their dose may need adjusting before or as soon as they become pregnant.
If you’ve had two or more miscarriages, testing for clotting disorders is standard. Conditions like antiphospholipid syndrome are manageable once identified. In women with specific clotting factor deficiencies, treatment reduced miscarriage from 80% down to 12.5% in one small but striking dataset. These are situations where the right diagnosis makes a dramatic difference.
Managing chronic conditions like diabetes, high blood pressure, and autoimmune diseases before conception, rather than after a positive test, gives the pregnancy the most stable start. The embryo’s most critical development happens in the first weeks, often before you even know you’re pregnant.
Lifestyle Choices That Matter
Smoking is the lifestyle factor with the clearest causal link to pregnancy loss. Genetic analysis studies have confirmed that smoking itself, not just the characteristics of people who smoke, directly increases the risk. Quitting before conception is ideal, but quitting at any point reduces harm.
The evidence on caffeine and alcohol is more nuanced than popular advice suggests. A large Mendelian randomization study, which uses genetic data to isolate cause and effect, found no significant causal association between moderate coffee or alcohol consumption and pregnancy loss. That said, most guidelines still recommend limiting caffeine to about 200 mg per day (roughly one 12-ounce coffee) and avoiding alcohol entirely during pregnancy, partly because “moderate” is hard to define and partly out of caution for other pregnancy outcomes beyond miscarriage.
Maintaining a healthy weight matters on both ends of the spectrum. Both very low and very high body weight are associated with higher miscarriage rates, likely through effects on hormone balance and ovulation quality.
Environmental Exposures Worth Reducing
A growing body of evidence connects certain industrial chemicals to pregnancy loss. Phthalates, found in plastics, personal care products, and food packaging, were associated with a 55% increase in miscarriage odds in a large meta-analysis. BPA, a compound in some plastics and can linings, was linked to miscarriage and other adverse pregnancy outcomes. PFAS chemicals, used in nonstick coatings and water-resistant fabrics, showed a smaller but measurable increase in risk.
Completely avoiding these chemicals is unrealistic since they’re widespread in modern life. But practical steps can reduce your exposure: choosing glass or stainless steel over plastic for food storage, avoiding heating food in plastic containers, selecting fragrance-free personal care products, and filtering drinking water. These steps won’t eliminate risk, but they lower the overall chemical burden during a vulnerable period.
Early Pregnancy Monitoring
Once you’re pregnant, early monitoring can’t prevent a missed miscarriage from happening, but it can catch warning signs sooner. In the first four weeks of pregnancy, the hormone hCG typically doubles every two to three days. After six weeks, doubling slows to roughly every four days. A rise of at least 53% over 48 hours confirms a viable pregnancy in 99% of cases. Levels that barely rise, for instance climbing from 120 to 130 over two days, suggest the pregnancy may not be developing normally.
If you’ve had previous losses, your provider may offer serial blood draws to track hCG trends and an early ultrasound around six to seven weeks. These won’t change the outcome if chromosomal problems are the cause, but they can shorten the agonizing period of uncertainty that defines a missed miscarriage. For many people, knowing sooner is itself a form of care.
After a Missed Miscarriage
If you’ve experienced a missed miscarriage and are wondering how to prevent another one, the most important thing to know is that a single loss, even a missed miscarriage, does not mean something is wrong with you. Most people who miscarry once go on to have a healthy pregnancy next time without any intervention.
After two or more consecutive losses, testing becomes more targeted. Karyotyping (chromosome analysis) of both partners, clotting panels, thyroid function tests, and imaging of the uterus can identify causes that would otherwise stay hidden. In roughly a third of recurrent loss cases, a specific, treatable factor is found. For the remaining two-thirds, the cause is usually repeated bad luck with chromosomal sorting, and the statistical odds still favor a successful future pregnancy.