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 naturally occurring events, not elective or therapeutic abortion procedures.

Other 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)
• infected abortion

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, hormonal 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 diseases such as diabetes or thyroid problems, and women with a history of three or more prior spontaneous abortions.

• Low-back pain or abdominal pain that is dull, sharp, or cramping
• Vaginal bleeding, with or without abdominal cramps
• Tissue or clot-like material that passes from the vagina

However, about 20% of pregnant women have some vaginal bleeding during the first trimester. Approximately half of these women have a spontaneous abortion.

During a pelvic exam, your healthcare provider may see moderate thinning of your cervix (effacement), increased cervical dilation, and evidence of ruptured membranes.

The following tests may be performed:

• HCG (qualitative urine) or HCG (qualitative blood serum) to confirm pregnancy
• HCG (quantitative) values drawn at intervals of days to weeks
• CBC to determine the degree of blood loss
• WBC and differential to rule out 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

The treatment for a threatened abortion varies from restricting some forms of exercise to complete bed rest. Abstaining from intercourse is usually recommended until the warning signs have disappeared.

If a spontaneous abortion occurs, the signs of pregnancy decrease, the uterus begins shrinking to its original size, and a brownish or reddish vaginal discharge is often experienced. The tissue passed from the vagina should be examined to determine the source (fetal vs. hydatidiform mole). It is also important to determine whether any fetal tissue remains in the uterus. This is called an incomplete spontaneous abortion.

If remaining tissue is not naturally aborted in a reasonable amount of time (about 4 weeks), surgery (D and C or D and E) or medication will be required to complete the abortion. Medications include mifepristone, methotrexate, misoprostol, or a combination of these medications. Most women who use these medications do so because of a desire to avoid anesthesia and surgery if at all possible.

Side effects of the medication may include nausea, vomiting, diarrhea, warmth or chills, headache, more visits to the doctor’s office, prolonged vaginal bleeding, and being more aware of cramping than with surgical abortion. With medication, passage of the products of conception most likely will occur at home, but some women may still require surgical evacuation (D and E) to complete the abortion. The success rate has been shown to be around 95%.

Once the tissue is removed, the woman usually resumes her normal menstrual cycle within a few weeks. Any further vaginal bleeding should be carefully monitored. It is often possible to become pregnant immediately, but the woman should usually wait for 1 or 2 normal menstrual cycles before trying to become pregnant again.

• Retained fetal tissue (an incomplete abortion) may cause an infection and must be removed surgically.
• An infection also may occur after a complete abortion.

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 spontaneous abortions that are caused by systemic diseases can be prevented by detecting and treating the disease before becoming pregnant.

Spontaneous abortions are less likely with early, comprehensive prenatal care and by avoiding environmental hazards (such as x-rays and infectious diseases).

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.