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Understanding Miscarriage -- the Basics

What Is a Miscarriage?

A miscarriage is a pregnancy that ends by itself within the first 20 weeks. "Stillbirth" refers to the loss of a pregnancy with fetal death that occurs after the first 20 weeks. Experts estimate that about half of all fertilized eggs die and are miscarried, usually even before the woman knows she is pregnant. Most miscarriages occur between the 7th and 12th weeks of pregnancy.

A miscarriage is a common experience. About 10% to 20% of pregnancies that a mother knows about -- because she has missed her period, her pregnancy has been confirmed by a health care provider, or both -- end in miscarriage. In most cases, miscarriage may be considered a "natural-selection" process, because it marks the ending of a pregnancy that would not have developed into a healthy baby. Only placental tissue, not a fetus, had formed.

The term "abortion" is commonly used to refer to the deliberate ending of a pregnancy. But, medically speaking, it refers to both the intentional and unintentional ending of a pregnancy, up until the time a fetus could be expected to survive outside the womb. Health care providers commonly use the medical term "spontaneous abortion" to refer to miscarriage.

What Causes a Miscarriage?

Most miscarriages occur when the unborn baby has fatal genetic problems. Usually, these problems are unrelated to the mother.

Other possible causes of miscarriage include:

  • Infection
  • Medical conditions in the mother, such as diabetes or thyroid disease
  • Hormonal factors
  • Immune responses
  • Physical problems in the mother

A woman has a higher risk of miscarriage if she:

  • Is over age 35
  • Has certain diseases, such as diabetes or thyroid problems
  • Has a history of three or more previous miscarriages

Cervical Insufficiency

A miscarriage sometimes occurs because there is a weakness of the cervix, called an incompetent cervix, which cannot hold the pregnancy. A miscarriage from an incompetent cervix usually occurs in the second trimester.

There are usually few symptoms prior to a miscarriage caused by cervical insufficiency. A woman may feel sudden pressure, her "water" may break, and tissue from the fetus and placenta may be expelled without too much pain. An incompetent cervix can usually be treated with a "circling" stitch in the cervix in the next pregnancy, usually around 12 weeks. The stitch holds the cervix closed until it is pulled out around the time of delivery.

What Are the Types of Miscarriage?

There are several stages and types of miscarriage. They include:

  • Threatened abortion. Early symptoms of a miscarriage occur, such as vaginal bleeding, but usually without other symptoms.
  • Inevitable abortion. The membranes have broken or the cervix has dilated too much.
  • Incomplete abortion. Some of the pregnancy tissue has been expelled, while other tissue remains in the uterus.
  • Complete spontaneous abortion. All of the pregnancy tissue is expelled from the uterus.
  • Missed abortion. The fetus has not developed or has died, but no bleeding or other symptoms are observed, and pregnancy tissue has not been expelled from the uterus.
  • Septic (infected) abortion. A serious infection has developed in the fetal material before, during, or after a miscarriage.


WebMD Medical Reference

Reviewed by Nivin Todd, MD, FACOG on March 11, 2014

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