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Abortion - spontaneous

Alternative names



A spontaneous abortion is the loss of a fetus during pregnancy due to natural causes. The term "miscarriage" is the spontaneous termination of a pregnancy before fetal development has reached 20 weeks. Pregnancy losses after the 20th week are categorized as preterm deliveries.

The term "spontaneous abortion" refers to these naturally occurring events, not elective or therapeutic abortion procedures.

More specific terms include: missed abortion (a pregnancy demise where nothing is expelled); incomplete abortion (not all of the products of conception are expelled); complete abortion (all of the products of conception are expelled); threatened abortion (symptoms indicate a miscarriage is possible); inevitable abortion (the symptoms cannot be stopped, and a miscarriage will happen); and infected abortion .

Causes, incidence, and risk factors

The cause of most spontaneous abortions is fetal death due to fetal genetic abnormalities, usually unrelated to the mother. Other possible causes for spontaneous abortion include: infection, physical problems the mother may have, hormone ( endocrine ) factors, immune responses, and serious systemic diseases of the mother (such as diabetes or thyroid problems).

It is estimated that up to 50% of all fertilized eggs die and are lost (aborted) spontaneously, usually before the woman knows she is pregnant. Among known pregnancies, the rate of spontaneous abortion is approximately 10% and usually occurs between the 7th and 12th weeks of pregnancy.

The risk for spontaneous abortion is higher in women over age 35, in women with systemic disease (such as diabetes or thyroid dysfunction), and women with a history of three or more prior spontaneous abortions.


  • Currently pregnant
  • Vaginal bleeding
    • With or without abdominal cramps
    • Between periods
  • Low back pain or abdominal pain
    • Dull or sharp or cramping
    • Persistent/constant or intermittent
  • Tissue or clot-like material that passes from the vagina

Note: Approximately 20% of pregnant women experience some vaginal bleeding during the first trimester. Less than half of these women have a spontaneous abortion .

Signs and tests

Pelvic examination may reveal moderate thinning of the cervix (effacement), increased cervical dilation, and evidence of ruptured membranes.

  • An HCG (qualitative - urine) or HCG (qualitative - serum) test confirms pregnancy
  • Serial HCG (quantitative) values may be drawn at intervals of days to weeks
  • A CBC may be done to determine the degree of blood loss
  • A WBC and differential may be done to rule out potential infection

An abortion, especially if incomplete or missed, may also alter the results of the following tests:

  • Transvaginal ultrasound
  • Pregnancy ultrasound
  • Estriol - urine
  • Estriol - serum
  • Serum progesterone
  • Fibrin degradation products


Treatment for threatened abortion varies from restrictions on some forms of exercise to complete bed rest. Abstaining from intercourse is usually recommended until signs have disappeared.

In the event of spontaneous abortion , the tissue passed from the vagina should be examined to determine the source of the tissue (fetal vs. hydatidiform mole ) and if any fetal tissue remains in the uterus ( incomplete abortion ).

Missed abortions that do not abort naturally and incomplete spontaneous abortions may require surgical removal of retained tissue ( D and C procedure). Any further vaginal bleeding should be carefully monitored.

Expectations (prognosis)

Maternal outcome is good and complications are rare. Waiting a few months before trying to become pregnant again is usually recommended.


  • Retained dead fetal tissue in the uterus is referred to as an incomplete abortion . This may cause infection and the retained uterine tissue must be removed surgically ( D and C ).
  • An infection may occur after either a complete or incomplete abortion.
  • In a missed abortion , the demise of the pregnancy is discovered before the appearance of any symptoms. A D and C , or a D and E can be performed to remove all of the dead tissue. Some patients choose to await spontaneous expulsion.
  • The death of a second or third trimester pregnancy is addressed differently than a first trimester loss. These are usually called intrauterine fetal demises (IUFD). If the dead fetus remains in the uterus for too long, an abnormal activation of blood clotting systems (coagulation and fibrinolytic systems) can develop in response to the release of anti-clotting chemicals from the retained dead fetus. This can adversely affect maternal health.

Calling your health care provider

Call your health care provider if vaginal bleeding with or without cramping occurs during pregnancy.

Call your health care provider if you are pregnant and notice tissue or clot-like material passed vaginally (any such material should be collected and brought in for examination).


Many of the spontaneous abortions that are caused by maternal disease can be prevented through early (prior to conception) detection and treatment of the disease.

Reduced risk of spontaneous abortions has been attributed to early, comprehensive prenatal care and avoidance of environmental hazards (such as X-rays and infectious diseases).

Spontaneous abortion naturally occurs after fetal death. The dead tissue is discarded from the uterus and the woman resumes her normal menstrual cycle within a few weeks (usually). Note: It is frequently possible to become pregnant immediately after a spontaneous abortion. However, it is recommended that a woman wait for one or two normal menstrual cycles before attempting another pregnancy.

On occasion, the uterus does not expel all of the fetal tissue, in which case it is considered an incomplete abortion. Incomplete spontaneous abortions may require surgical removal of the retained tissue.

Pregnancy loss at any gestational age may not be accompanied by prompt expulsion of the dead tissue. Signs of pregnancy decrease, the uterus begins shrinking to its original size, and a brownish or reddish vaginal discharge is often experienced. If spontaneous abortion does not occur in a reasonable amount of time (about 4 weeks), a D and C , or D and E will have to be performed, or labor induced to remove the dead fetus.

When a mother's body is having difficulty sustaining a pregnancy, signs (such as slight vaginal bleeding ) may occur. This is a threatened abortion , which means there is a possibility of abortion, but it is not inevitable. A pregnant woman who develops any signs or symptoms of threatened miscarriage should contact her prenatal provider immediately.

Update Date: 1/27/2002

Dominic Marchiano, M.D., Department of Obstetrics & Gynecology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT