Miscarriage Causes

Medically Reviewed by Dan Brennan, MD on August 09, 2022
5 min read

If you're pregnant, you may be concerned about the risks of a miscarriage or pregnancy loss. (It’s called “miscarriage” when the pregnancy ends before the 20th week). Most of the time, this happens for reasons you have no control over. In fact, it's often difficult to pinpoint the exact cause. Learning what causes it may help put your mind at ease and help you improve your chances for having a healthy, full-term pregnancy.

Here's an overview of some of the most common causes of pregnancy loss.

When a miscarriage happens in the first 12 weeks, more than half the time it’s because of a problem with the baby's chromosomes. Chromosomes contain the genes that determine your baby's unique traits, such as hair and eye color. A baby can't grow normally with the wrong number of chromosomes or with damaged ones.

An abnormality in a unborn baby’s chromosomes could cause one of several problems. Among the most common are:

  • Blighted ovum(anembryonic pregnancy). No embryo develops.
  • Molar pregnancy. Both sets of chromosomes come from the father, while none come from the mother. The placenta doesn’t grow normally, and the fetus doesn’t develop.
  • Partial molar pregnancy. The father gives two sets of chromosomes in addition to the set from the mother. The embryo may start to develop but soon stops.

Several other chromosomal abnormalities can cause the loss of a pregnancy. These include trisomy 13, 18, 21 (Down syndrome), monosomy (Turner's syndrome), and other sex chromosome issues.

Here are some other things to keep in mind about abnormal chromosomes:

  • There's no way to prevent chromosome problems from happening.
  • As you get older, especially after age 35, your risk for chromosome problems specifically, and pregnancy loss in general, goes up.

Miscarriages from chromosome problems usually don't happen again in future pregnancies.

A pregnancy loss often results from a problem with the mother’s health. Some of these include:

Your habits as the mom-to-be can increase the risk of a pregnancy loss. Here are some habits that are dangerous for a developing baby:

In addition to secondhand smoke, certain substances in your environment at home or at work could put your pregnancy at risk. These include:

  • Lead in old water pipes or paint in homes built before 1978
  • Mercury released from broken thermometers or fluorescent light bulbs
  • Solvents such as paint thinners, degreasers, and stain and varnish removers
  • Pesticides for killing insects or rodents
  • Arsenic found near waste sites or in some well water

Be sure to talk with your doctor about this. You may find your risks are not as great as you think.

Several prescription and over-the-counter medications can raise your chances of miscarriage and pregnancy loss, including:

Several types of food poisoning during pregnancy can raise your risk for miscarriage or pregnancy loss.

  • Listeriosis. Typically found in unpasteurized soft cheeses such as blue, Brie, or queso fresco, and raw or undercooked seafood
  • Salmonella. Usually found in raw or undercooked eggs
  • Toxoplasmosis. Most often caused by eating infected raw meat

Some food poisoning illnesses, including listeriosis and toxoplasmosis, can infect your unborn baby even if you don’t have symptoms yourself.

Follow your doctor’s guidelines about cooking and foods to stay away from while you’re pregnant.

You may worry that certain activities or emotions might raise the risk to your pregnancy. But if your pregnancy isn’t considered high-risk, the following things are generally safe:

  • Working
  • Sitting or standing for reasonable amounts of time
  • Exercise (talk with your doctor about what level of exercise is right for you)
  • Having sex
  • Air travel
  • Eating spicy food
  • Having an emotional shock or scare
  • Stress or depression

Although there's no sure way to prevent miscarriage or pregnancy loss, you can take steps to help ensure a healthy pregnancy:

  • Have a pre-conception checkup.
  • Have regular prenatal visits so your doctor can help prevent and treat any problems early. Make taking care of existing health problems a priority. Your efforts will give your baby the best chance for health.
  • Curb dangerous lifestyle habits. If you can't stop on your own, talk with your doctor about getting help to stop.
  • Ask your doctor about your risk from the environment and how to protect yourself.
  • Ask your doctor whether you should see an obstetrical specialist, such as a perinatologist, especially if you have more than one miscarriage. These doctors specialize in complicated pregnancies.
  • Take a daily multivitamin.
  • Limit caffeine.
  • Eat a healthy, balanced diet.
  • Avoid certain foods that can carry bacteria.
  • Maintain a healthy weight.
  • Be aware that you can do everything "right" and still have a miscarriage. Try not to add guilt or self-blame to your emotional burden. Between working with your doctor and making healthy lifestyle changes, you can rest easy knowing you've done everything you can to have a healthy pregnancy.