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Spontaneous Abortion

(Miscarriage; Pregnancy Loss)

By

Aparna Sridhar

, MD, UCLA Health

Reviewed/Revised Oct 2023
View PATIENT EDUCATION
Topic Resources

Spontaneous abortion is pregnancy loss before 20 weeks gestation. Diagnosis is by pelvic examination, measurement of beta subunit of human chorionic gonadotropin, and ultrasonography. Treatment may be expectant management or with medication or procedural uterine evacuation.

The American College of Obstetricians and Gynecologists defines a first-trimester pregnancy loss as a nonviable, intrauterine pregnancy with either an empty gestational sac or a gestational sac containing an embryo or fetus without fetal heart activity within the first 12 6/7 weeks of gestation (3 General references Spontaneous abortion is pregnancy loss before 20 weeks gestation. Diagnosis is by pelvic examination, measurement of beta subunit of human chorionic gonadotropin, and ultrasonography. Treatment... read more ).

Terminology for abortion varies based on several factors. Definitions specify the stage of development, embryonic (≤ 10 weeks of gestation) or fetal (≥ 11 weeks). For spontaneous abortion, descriptions are based on the location of the fetus and other products of conception and whether there is cervical dilation (see table ).

Table

General references

Etiology of Spontaneous Abortion

Early spontaneous abortion is often caused by a chromosomal abnormality Overview of Chromosomal Abnormalities Chromosomal abnormalities cause various disorders. Abnormalities that affect autosomes (the 22 paired chromosomes that are alike in males and females) are more common than those that affect... read more . Maternal reproductive tract abnormalities (eg, bicornuate uterus, fibroids, adhesions) may also cause pregnancy loss through 20 weeks gestation. Isolated spontaneous abortions may result from certain viral infections—most notably cytomegalovirus, herpesvirus, parvovirus, and rubella virus. Other causes include immunologic abnormalities and major physical trauma. Most often, the cause is unknown.

Risk factors for spontaneous abortion include

In a national database study, the risks of miscarriage across maternal age groups were as follows: < 20 years (17%); 20 to 24 (11%); 25 to 29 (10%); 30 to 34 (11%); 35 to 39 (17%); 40 to 44 (33%); > 45 (57%) (1 Etiology reference Spontaneous abortion is pregnancy loss before 20 weeks gestation. Diagnosis is by pelvic examination, measurement of beta subunit of human chorionic gonadotropin, and ultrasonography. Treatment... read more ).

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

Etiology reference

Symptoms and Signs of Spontaneous Abortion

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, uterine bleeding may occur, sometimes after a delay of hours to days. Infection may also develop, causing fever, pain, and sometimes sepsis (called septic abortion Septic Abortion Septic abortion is serious uterine infection during or shortly before or after a spontaneous or an induced abortion. Septic abortion is a gynecologic emergency. Septic abortions usually result... read more ).

Symptoms and signs reference

  • 1. Hasan R, Baird DD, Herring AH, et al: Patterns and predictors of vaginal bleeding in the first trimester of pregnancy. Ann Epidemiol 20(7):524-531, 2010. doi:10.1016/j.annepidem.2010.02.006

Diagnosis of Spontaneous Abortion

  • Transvaginal ultrasonography

  • Quantitative beta subunit of human chorionic gonadotropin (beta-hCG)

  • Pelvic examination

Pregnancy is diagnosed with a urine or serum beta-hCG test. Transvaginal ultrasonography is the main method used to evaluate for spontaneous abortion. If ultrasonography is not available, hCG results may be informative. There is no single hCG level that is diagnostic of spontaneous abortion; serial beta-hCG levels that decrease across several measurements are consistent with a failed pregnancy.

Transvaginal ultrasonography is performed to confirm intrauterine pregnancy and check for fetal cardiac activity, which is usually detectable after 5.5 to 6 weeks gestation. However, gestational age is often somewhat uncertain, and serial ultrasonography is often required. If cardiac activity is absent and had been detected previously during the current pregnancy, fetal demise is diagnosed.

In early pregnancy, for patients with suspected spontaneous abortion, transvaginal ultrasound findings diagnostic of pregnancy failure are one or more of the following (1 Diagnosis reference Spontaneous abortion is pregnancy loss before 20 weeks gestation. Diagnosis is by pelvic examination, measurement of beta subunit of human chorionic gonadotropin, and ultrasonography. Treatment... read more ):

  • Crown-rump length ≥ 7 mm and no heartbeat

  • Mean sac diameter ≥ 25 mm and no embryo

  • Absence of an embryo with a heartbeat, after a previous scan in current pregnancy: ≥ 2 weeks earlier that showed a gestational sac without a yolk sac OR ≥ 11 days earlier in the current pregnancy that showed a gestational sac with a yolk sac

There are many ultrasound findings that raise suspicion for but are not diagnostic of pregnancy failure, including characteristics of the gestational or yolk sac, absence of embryo or heartbeat, and crown-rump length. If these findings are present, serial evaluation is required to confirm whether a pregnancy is viable.

Traditionally, the status of the abortion process is classified as follows:

  • Threatened abortion: Patients have uterine bleeding and it is too early to assess whether the fetus is alive and viable and the cervix is closed. Potentially, the pregnancy may continue without complications.

  • Inevitable abortion: The cervix is dilated. If the cervix is dilated, the volume of bleeding should be evaluated because it is sometimes significant.

  • Incomplete abortion: The products of conception are partially expelled.

  • Complete abortion: The products of conception have passed and the cervix is closed (see table ).

  • Missed abortion: Death of an embryo or a fetus is confirmed, but there is no bleeding or cervical dilation and the products of conception have not been expelled.

Table

An anembryonic pregnancy (formerly blight ovum) refers to a nonviable pregnancy with a gestational sac, but with no yolk sac or embryo visualized on transvaginal ultrasonography.

Differential diagnosis

Table
Table

Diagnosis reference

Treatment of Spontaneous Abortion

  • For threatened abortion, observation

  • For inevitable, incomplete, or missed abortions, observation or surgical or medical uterine evacuation

  • If the mother is Rh-negative, Rho(D) immune globulin

  • Pain medication as needed

  • Emotional support

For threatened abortion, treatment is observation, but clinicians may periodically evaluate the woman's symptoms or do ultrasonography to check fetal status. No evidence suggests that bed rest decreases risk of subsequent completed abortion.

For inevitable, incomplete, or missed abortions, treatment is waiting for spontaneous passage of products of conception, management with medications, or uterine evacuation.

In the first trimester, expectant management is an option, but this approach is not recommended during the second trimester due to limited safety studies and risk of hemorrhage (1 Treatment references Spontaneous abortion is pregnancy loss before 20 weeks gestation. Diagnosis is by pelvic examination, measurement of beta subunit of human chorionic gonadotropin, and ultrasonography. Treatment... read more ). Expectant management has an 80% success rate for complete expulsion within 8 weeks, with symptomatic women having better outcomes than asymptomatic women. Bleeding and cramping may occur, and patients should be counseled about when to return to the healthcare facility if symptoms are severe or to confirm passage of gestational tissue. Ultrasound and reported symptoms are used to confirm passage of gestational tissue; in a patient with a previous ultrasound that showed a gestational sac, a follow-up ultrasound with no gestational sac is the most common criterion for complete expulsion. For patients who cannot return for ultrasound confirmation, triaging via telemedicine and/or home urine pregnancy tests may be useful. If complete expulsion is not achieved within a reasonable time, medical management or surgery may be necessary.

Until 10 to 12 weeks gestation, medical management may be used if spontaneous expulsion does not occur or if a patient prefers use of medications to allow a more predictable process. A common medication regimen is 800 mcg of misoprostol vaginally; a repeat dose may be necessary. Administering 200 mg of mifepristone orally 24 hours before the misoprostol can significantly improve treatment success, if mifepristone is available (1 Treatment references Spontaneous abortion is pregnancy loss before 20 weeks gestation. Diagnosis is by pelvic examination, measurement of beta subunit of human chorionic gonadotropin, and ultrasonography. Treatment... read more ).

Spontaneous abortions that are not completely expelled with expectant management or medications require surgical uterine evacuation. Also, some women may prefer surgical evacuation due to more immediate completion and less need for follow-up care. Traditionally, uterine evacuation was performed with sharp curettage alone. However, suction curettage Instrumental evacuation In the United States, about half of pregnancies are unintended. About 40% of unintended pregnancies end in induced abortion; 90% of procedures are done during the 1st trimester. In the United... read more is now favored due to superior outcomes and can be completed in an office setting with local anesthesia and/or sedation in first trimester loss patients.

Urgent surgical evacuation may be needed in cases of hemorrhage, hemodynamic instability, or infection.

If complete abortion seem likely based on symptoms and/or ultrasound, further management with medications or uterine evacuation is typically not required. Uterine evacuation may be needed if bleeding occurs and/or if other signs indicate that products of conception may be retained.

After a spontaneous abortion, parents may feel grief or guilt. They should be given emotional support and, in most cases of spontaneous abortions, reassured that their actions were not the cause. Formal counseling or support groups may be made available if appropriate.

Treatment references

Key Points

  • Spontaneous abortion is pregnancy loss before 20 weeks gestation; it occurs in approximately 10 to 15% of confirmed pregnancies.

  • Spontaneous abortion is often caused by chromosomal abnormalities or maternal reproductive tract abnormalities (eg, bicornuate uterus, fibroids), but etiology in an individual case is usually not confirmed.

  • Confirm spontaneous abortion and determine pregnancy status with quantitative beta-hCG, ultrasonography, and pelvic examination; a dilated cervix means that abortion is inevitable.

  • Treat with expectant management (observe for passage of products of conception) or surgical or medication (with misoprostol or sometimes mifepristone) uterine evacuation.

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

  • Provide emotional support to the parents.

Drugs Mentioned In This Article

Drug Name Select Trade
Novarel, Ovidrel, Pregnyl
GOPRELTO, NUMBRINO
Cytotec
Korlym, Mifeprex
View PATIENT EDUCATION
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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