What can cause a miscarriage (and what can’t)

When miscarriages happen, the cause may not always be clear. What we do know is that a miscarriage is often caused by a factor that the pregnant woman and her care team have no control over, which may feel both comforting and frustrating if you ever experience pregnancy loss. In fact, most miscarriages occur within the first 8 weeks of pregnancy, before some women even know they’re pregnant.

Read on to learn about the most common causes of miscarriage and the risk factors associated with them. We’ll also go over what doesn’t cause a miscarriage.

Common causes of miscarriage

A miscarriage is clinically considered the loss of a pregnancy before week 20 of gestation. While many times the cause of a miscarriage is unknown, sometimes doctors are able to determine what may have contributed to the loss.

Chromosomal abnormalities are the most common cause of miscarriage

Chromosomal abnormalities refer to a random error in how cells start dividing early in a pregnancy. If a miscarriage is due to a chromosomal abnormality, that doesn’t mean there’s a higher chance of it happening again, unless there are other known factors. But types of miscarriage can be more common in patients who are in their late 30s or 40s due to the age of the eggs themselves.

Uterine or cervical issues can make it difficult for a pregnancy to progress

In some cases, conditions related to the uterus or cervix can interfere with embryo development and lead to miscarriage. This includes conditions that create scar tissue in the uterus such as endometriosis and pelvic inflammatory disease, and cervical insufficiency, which is when the cervix cannot stay tightly closed. With cervical insufficiency, sometimes pregnancy loss is inevitable because the body cannot hold the baby in long enough to reach viability.

Bacterial and viral infections can sometimes lead to miscarriage

Certain types of bacterial infections can cause miscarriage, including listeriosis, a type of food poisoning. The pregnant woman can get it from eating food contaminated with listeria bacteria, which can cross the placenta and infect the baby. Most foods are safe to eat during pregnancy, but the Food and Drug Administration recommends that you avoid eating certain foods during pregnancy that have a higher risk of being contaminated with listeria bacteria, including deli meats and hotdogs (unless they’re heated to steaming), raw milk or cheeses like queso fresco, meat plates and cold smoked fish.

Untreated urinary tract infections or sexually transmitted infections can also cause miscarriage. These types of infections often don’t have any symptoms, which is why it’s important to get tested for STIs before you become pregnant and as part of your prenatal care.

Injury or trauma to the abdomen can sometimes cause miscarriage

Your baby is very well protected in your body, but serious trauma or injury to the abdominal area – like from a car crash, direct abdominal blow or a fall on your belly – can cause miscarriage. But typically, these risks don’t increase until late in the second trimester or early third trimester when your belly is more visible.

Certain health conditions can increase your risk of miscarriage

Certain health conditions – like autoimmune disorders, thyroid disorders, severe diabetes, high blood pressure, and being over or underweight – can contribute to the possibility of miscarriage.

If you have a chronic health condition and are planning to become pregnant, schedule a preconception visit with your doctor or clinician to learn if there’s anything you can do to decrease your risks of miscarrying. If you’re currently pregnant, your doctor can work with you to minimize your risk of miscarriage.

Risk factors that can increase the possibility of miscarriage

While it’s not possible to avoid all risk factors during pregnancy, there are factors you can control to promote a healthy pregnancy and avoid pregnancy complications as best as you can. Some risk factors include:

Smoking, drinking alcohol or using drugs while pregnant – Use of these substances is associated with a higher risk of miscarriage. Using less or stopping substance use altogether increases the chances of a healthy pregnancy.
Environmental exposure – This includes both working around or otherwise being exposed to radiation, toxins or contaminants.
Consecutive miscarriages – Having two or more miscarriages in a row may be a sign that you have a higher chance of miscarrying in general.
Being older than age 35 – Pregnancy after age 35 comes with a higher risk of miscarriage. This is because you’re born with all the eggs you’ll ever have and those eggs age with you. Older eggs have a high chance of genetic problems.
Use of an IUD – Pregnancy with and IUD in place is incredibly uncommon, less than 1%. However, of the pregnancies that do occur with an IUD in place, ectopic and miscarriage rates are higher.

What doesn’t cause a miscarriage?

Most everyday activities are safe to continue throughout pregnancy. Common things not linked to miscarriage include:

Air travel – In general, it’s safe for pregnant women to travel (even by air) until 36 weeks gestation. But it’s important to keep your ankles and legs moving every hour because you’re at a higher risk of blood clot from sitting for a long time.
Exercise and moderate physical activity – Regular physical activity can have a lot of benefits during pregnancy. It can help ease aches and pains, strengthen muscles and help you gain weight that’s healthy for your pregnancy. It can also set you up for an easier recovery once your baby is here. However, starting a new or more rigorous exercise program during pregnancy isn’t recommended. If you have questions about safely exercising while pregnant, talk with your doctor.
Caffeine use – Research on caffeine causing complications during pregnancy is inconclusive. So until we know more, you don’t need to cut out your caffeine use completely. Try to limit it to 200 mg of caffeine or less per day, and don’t forget that caffeine is in more than just coffee, so read labels carefully.
Sexual intercourse – Sex is usually considered safe at every stage of pregnancy because your baby is well protected inside your body. Cramps and spotting are possible after sex while pregnant, but if you experience heavier bleeding or intense cramping, speak to your doctor right away.
Anxiety, depression or other mood disorders – During pregnancy, your hormones are fluctuating rapidly, which can cause your mood and emotions to also fluctuate. Although it might not feel like it, this is common and happens to almost all pregnant women. There are things you can do to help improve your mental health, so speak with your doctor as soon as you notice any changes in your mood.
Employment – Unless you have a highly physical job, or one where you’re on your feet for long periods of time, your pregnancy generally shouldn’t prevent you from your normal duties. This can change later in your pregnancy, so make sure to speak with your doctor regarding limitations.
Past termination of pregnancy – A past termination shouldn’t raise your risk of miscarriage or ectopic pregnancy.
Past use of hormonal birth control – Even if you’ve used them for a prolonged period of time, hormonal birth control doesn’t have any long-term impacts on your ability to conceive, or increase your risk of having a miscarriage. When you stop using them, your fertility should return relatively quickly.

Talk with your doctor about miscarriage causes and risks

It’s always a good idea to talk with your doctor or clinician and listen to their advice and recommendations. Reach out to your doctor if you have any questions or concerns, no matter how small they may seem.