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Spontaneous Abortion



Antonette T. Dulay

, MD, Main Line Health System

Last full review/revision Oct 2020| Content last modified Oct 2020
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Spontaneous abortion is noninduced embryonic or fetal death or passage of products of conception before 20 weeks gestation. Threatened abortion is vaginal bleeding without cervical dilation occurring during this time frame and indicating that spontaneous abortion may occur in a woman with a confirmed viable intrauterine pregnancy. Diagnosis is by clinical criteria and ultrasonography. Treatment is usually expectant observation for threatened abortion and, if spontaneous abortion has occurred or appears unavoidable, observation or uterine evacuation.

Spontaneous abortion, by definition, is death of the fetus; it may increase the risk of spontaneous abortion in subsequent pregnancies.

Fetal death and early delivery are classified as follows:

  • Abortion: Death of the fetus or passage of products of conception (fetus and placenta) before 20 weeks gestation

  • Fetal demise (stillbirth): Fetal death after 20 weeks

  • Preterm delivery: Passage of a live fetus between 20 weeks and 36 weeks/6 days

Abortions may be classified as follows (see table Classification of Abortion):

  • Early or late

  • Spontaneous or induced for therapeutic or elective reasons

  • Threatened or inevitable

  • Incomplete or complete

  • Recurrent (also called recurrent pregnancy loss)

  • Missed


Classification of Abortion




Abortion before 12 weeks gestation


Abortion between 12 and 20 weeks gestation


Noninduced abortion


Termination of pregnancy for medical or elective reasons


Termination of pregnancy because the woman’s life or health is endangered or because the fetus is dead or has malformations incompatible with life


Vaginal bleeding occurring before 20 weeks gestation without cervical dilation and indicating that spontaneous abortion may occur


Vaginal bleeding or rupture of the membranes accompanied by dilation of the cervix


Expulsion of some products of conception


Expulsion of all products of conception

Recurrent or habitual

≥ 2 to 3 consecutive spontaneous abortions


Undetected death of an embryo or a fetus that is not expelled and that causes no bleeding (also called blighted ovum, anembryonic pregnancy, or intrauterine embryonic demise)


Serious infection of the uterine contents during or shortly before or after an abortion

About 20 to 30% of women with confirmed pregnancies bleed during the first 20 weeks of pregnancy; half of these women spontaneously abort. Thus, incidence of spontaneous abortion is up to about 20% in confirmed pregnancies. Incidence in all pregnancies is probably higher because some very early abortions are mistaken for a late menstrual period.


Isolated spontaneous abortions may result from certain viruses—most notably cytomegalovirus, herpesvirus, parvovirus, and rubella virus—or from disorders that can cause sporadic abortions or recurrent pregnancy loss (eg, chromosomal or mendelian abnormalities, luteal phase defects). Other causes include immunologic abnormalities, major trauma, and uterine abnormalities (eg, fibroids, adhesions). Most often, the cause is unknown.

Risk factors for spontaneous abortion include

Subclinical thyroid disorders, a retroverted uterus, and minor trauma have not been shown to cause spontaneous abortions.

Symptoms and Signs

Symptoms of spontaneous abortion include crampy pelvic pain, bleeding, and eventually expulsion of tissue. Late spontaneous abortion may begin with a gush of fluid when the membranes rupture. Hemorrhage is rarely massive. A dilated cervix indicates that abortion is inevitable.

If products of conception remain in the uterus after spontaneous abortion, vaginal bleeding may occur, sometimes after a delay of hours to days. Infection may also develop, causing fever, pain, and sometimes sepsis (called septic abortion).


  • Clinical criteria

  • Usually ultrasonography and quantitative beta subunit of human chorionic gonadotropin (beta-hCG)

Diagnosis of threatened, inevitable, incomplete, or complete abortion is often possible based on clinical criteria (see table Characteristic Symptoms and Signs in Spontaneous Abortions) and a positive urine pregnancy test.

Ultrasonography and quantitative measurement of serum beta-hCG are usually also done to exclude ectopic pregnancy and to determine whether products of conception remain in the uterus (suggesting that abortion is incomplete rather than complete). However, results may be inconclusive, particularly during early pregnancy.


Characteristic Symptoms and Signs in Spontaneous Abortions

Type of Abortion

Vaginal Bleeding

Cervical Dilation*

Passage of Products of Conception†















Y or N



Y or N



* Internal cervical os is open enough to admit a fingertip during digital examination.

† Products of conception may be visible in the vagina. Tissue examination is sometimes required to differentiate blood clots from tissue products of conception. Before the evaluation, products of conception may have been expelled without the patient recognizing them.

Missed abortion is suspected if the uterus does not progressively enlarge or if quantitative beta-hCG is low for gestational age or does not double within 48 to 72 hours. Missed abortion is confirmed if ultrasonography shows any of the following:

  • Disappearance of previously detected embryonic cardiac activity

  • Absence of such activity when the fetal crown-rump length is > 7 mm

  • Absence of a fetal pole (determined by transvaginal ultrasonography) when the mean sac diameter (average of diameters measured in 3 orthogonal planes) is > 25 mm

For recurrent pregnancy loss, testing to determine the cause of abortion is necessary.


  • Observation for threatened abortion

  • Uterine evacuation for inevitable, incomplete, or missed abortions

  • Emotional support

For threatened abortion, treatment is observation. No evidence suggests that bed rest decreases risk of subsequent completed abortion.

For inevitable, incomplete, or missed abortions, treatment is uterine evacuation or waiting for spontaneous passage of the products of conception. Evacuation usually involves suction curettage at < 12 weeks, dilation and evacuation at 12 to 23 weeks, or medical induction at > 16 to 23 weeks (eg, with misoprostol). The later the uterus is evacuated, the greater the likelihood of placental bleeding, uterine perforation by long bones of the fetus, and difficulty dilating the cervix. These complications are reduced by preoperative use of osmotic cervical dilators (eg, laminaria), misoprostol, or mifepristone (RU 486).

If complete abortion is suspected, uterine evacuation need not be done routinely. Uterine evacuation can be done if bleeding occurs and/or if other signs indicate that products of conception may be retained.

After an induced or spontaneous abortion, parents may feel grief and guilt. They should be given emotional support and, in most cases of spontaneous abortions, reassured that their actions were not the cause. Formal counseling is rarely indicated but should be made available.

Key Points

  • Spontaneous abortion probably occurs in about 10 to 15% of pregnancies.

  • The cause of an isolated spontaneous abortion is usually unknown.

  • A dilated cervix means that abortion is inevitable.

  • Confirm spontaneous abortion and determine its type based on clinical criteria, ultrasonography, and quantitative beta-hCG.

  • Uterine evacuation is eventually necessary for inevitable, incomplete, or missed abortions.

  • Often, uterine evacuation is not needed for threatened and complete abortions.

  • After spontaneous abortion, provide emotional support to the parents.

Recurrent Pregnancy Loss

(Recurrent or Habitual Abortion)

Recurrent pregnancy loss is 2 to 3 consecutive spontaneous abortions. Determining the cause may require extensive evaluation of both parents. Some causes can be treated.


Causes of recurrent pregnancy loss may be maternal, fetal, or placental.

Common maternal causes include

  • Uterine or cervical abnormalities (eg, polyps, myomas, adhesions, cervical insufficiency)

  • Maternal (or paternal) chromosomal abnormalities (eg, balanced translocations)

  • Overt and poorly controlled chronic disorders (eg, hypothyroidism, hyperthyroidism, diabetes mellitus, hypertension)

  • Chronic renal disorders

Acquired thrombotic disorders (eg, related to antiphospholipid antibody syndrome with lupus anticoagulant, anticardiolipin [IgG or IgM], or anti-beta2 glycoprotein I [IgG or IgM]) are associated with recurrent losses after 10 weeks. The association with hereditary thrombotic disorders is less clear but does not appear to be strong, except for possibly factor V Leiden mutation.

Placental causes include preexisting chronic disorders that are poorly controlled (eg, systemic lupus erythematosus [SLE], chronic hypertension).

Fetal causes are usually

  • Chromosomal or genetic abnormalities

  • Anatomic malformations

Chromosomal abnormalities may cause 50% of recurrent pregnancy losses; losses due to chromosomal abnormalities are more common during early pregnancy. Aneuploidy is involved in up to 80% of all spontaneous abortions occurring at < 10 weeks gestation but in < 15% of those occurring at ≥ 20 weeks.

Whether a history of recurrent pregnancy loss increases risk of fetal growth restriction and premature delivery in subsequent pregnancies depends on the cause of the losses.


  • Clinical evaluation

  • Tests to identify the cause

The diagnosis of recurrent pregnancy loss is clinical.

Evaluation for recurrent pregnancy loss should include the following to help determine the cause:

  • Genetic evaluation (karyotyping) of both parents and any products of conception as clinically indicated to exclude possible genetic causes

  • Screening for acquired thrombotic disorders: Anticardiolipin antibodies (IgG and IgM), anti-beta2 glycoprotein I (IgG and IgM), and lupus anticoagulant

  • Thyroid-stimulating hormone

  • Diabetes testing

  • Hysterosalpingography or sonohysterography to check for structural uterine abnormalities

Cause cannot be determined in up to 50% of women. Screening for hereditary thrombotic disorders is no longer routinely recommended unless supervised by a maternal-fetal medicine specialist.


  • Treatment of the cause if possible

Some causes of recurrent pregnancy loss can be treated. If the cause cannot be identified, the chance of a live birth in the next pregnancy is 35 to 85%.

Key Points

  • Causes of recurrent pregnancy loss may be maternal, fetal, or placental.

  • Chromosomal abnormalities (particularly aneuploidy) may cause 50% of recurrent pregnancy losses.

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