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4 Common Causes of Miscarriage

Now that you're pregnant, you may be concerned about the risks of a miscarriage. Most miscarriages occur for reasons you have no control over. In fact, it's often difficult to pinpoint the exact cause. Learning what causes miscarriage 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 four of the most common causes of miscarriage.

Cause No. 1: Abnormal Chromosomes

More than half of miscarriages in the first 13 weeks of pregnancy occur because of a problem with the babies' chromosomes. Chromosomes contain the genes that determine your babies' unique traits, such as hair and eye color. Babies can't grow normally with the wrong number of chromosomes or with damaged ones.

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 miscarriage in general, increases.

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

Cause No. 2: Medical Conditions

A miscarriage during weeks 13 through 24, the second trimester, often results from a problem with the mother. These are some health problems that increase a woman's risk for miscarriage.

  • An infection such as cytomegalovirus or German measles.
  • Hormone problems that prevent the lining of your uterus from thickening, which the fertilized egg or eggs need to implant.
  • Poorly controlled chronic diseases such as diabetes or high blood pressure.
  • Thyroid disease, lupus, and other autoimmune disorders.
  • Problems with your uterus or cervix, such as fibroids; an abnormally shaped uterus; or a cervix that opens and widens too early, called incompetent cervix.

Cause No. 3: Lifestyle

Your habits as the mom-to-be can increase the risk of miscarriage. Here are some habits that are dangerous for developing babies:

  • Smoking. Some studies show an increased risk of miscarriage even if only the father smokes.
  • Heavy drinking
  • Using illegal drugs

Cause No. 4: Environmental Hazards

In addition to secondhand smoke, certain substances in your environment at home or at work may also put your pregnancy at risk for miscarriage. 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.

What Can I Do to Protect My Pregnancy?

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

  • Have a preconception 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 babies 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.

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.

WebMD Medical Reference

Reviewed by Traci C. Johnson, MD, FACOG on August 01, 2014

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