Spontaneous abortion
Approximately 10 to 15% of confirmed pregnancies spontaneously abort, and over 80% of spontaneous abortions occur in the first trimester (1).
Fetal death and early delivery are classified as follows (2, 3):
Spontaneous abortion: Pregnancy loss before 20 weeks gestation
Fetal death (stillbirth): Fetal death at ≥ 20 weeks
Preterm delivery: Delivery of a live fetus between 20 weeks and 36 weeks/6 days
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).
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 Classification of Abortion).
Classification of Abortion
Type | Definition |
|---|---|
Early | Abortion before 12 weeks gestation |
Late | Abortion between 12 and 20 weeks gestation |
Spontaneous | Pregnancy loss at < 20 weeks gestation |
| Vaginal bleeding occurring before 20 weeks gestation without cervical dilation |
| Vaginal bleeding or rupture of the membranes before 20 weeks gestation accompanied by advanced dilation of the cervix |
| Dilation of cervix and expulsion of some products of conception |
| Closed cervix after expulsion of all products of conception |
| 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 |
| Nonviable pregnancy with a gestational sac, but with no yolk sac or embryo visualized on transvaginal ultrasonography |
| ≥ 2 to 3 spontaneous abortions |
Induced | Interruption of pregnancy with medications or a procedure |
Septic | Serious infection of the uterine contents during or shortly before or after an abortion |
General references
1. Magnus MC, Wilcox AJ, Morken NH, et al: Role of maternal age and pregnancy history in risk of miscarriage: Prospective register based study. BMJ 364:l869, 2019. doi: 10.1136/bmj.l869
2. First- and Second-Trimester Pregnancy Loss. In: Cunningham F, Leveno KJ, Dashe JS, Hoffman BL, Spong CY, Casey BM, eds. Williams Obstetrics, 26e. McGraw Hill; 2022. Accessed August 28, 2023.
3. American College of Obstetricians and Gynecologists (ACOG): ACOG Practice Bulletin No. 200 Summary: Early Pregnancy Loss. Obstet Gynecol 132(5):1311-1313, 2018. doi:10.1097/AOG.0000000000002900
Etiology of Spontaneous Abortion
Early spontaneous abortion is often caused by a chromosomal abnormality. 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
Extremes of maternal age
History of spontaneous abortion
Cigarette smoking
Use of certain substances (eg, , alcohol)
A poorly controlled chronic disease (eg, diabetes, hypertension, overt thyroid disorders) in the mother
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).
Subclinical thyroid disorders, a retroverted uterus, and minor trauma have not been shown to cause spontaneous abortions.
Etiology reference
1. Magnus MC, Wilcox AJ, Morken NH, et al: Role of maternal age and pregnancy history in risk of miscarriage: Prospective register based study. BMJ 364:l869, 2019. doi: 10.1136/bmj.l869
Symptoms and Signs of Spontaneous Abortion
Symptoms of spontaneous abortion include crampy pelvic pain, uterine bleeding, and eventually expulsion of tissue.
Bleeding in early pregnancy is common; in one study of over 4500 women, bleeding occurred in approximately 25% of first-trimester pregnancies, and 12% of pregnancies with bleeding resulted in pregnancy loss (1).
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).
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
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):
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 Characteristic Symptoms and Signs in Spontaneous Abortions).
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.
Characteristic Symptoms and Signs in Spontaneous Abortions
Type of Abortion | Vaginal Bleeding | Cervical Dilation* | Passage of Products of Conception† |
|---|---|---|---|
Threatened | Y | N | N |
Inevitable | Y | Y | N |
Incomplete | Y | Y | Y† |
Complete | Y | Y or N | Y |
Missed | Y or N | N | 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. | |||
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.
For recurrent pregnancy loss, typically testing is done to determine the cause of abortion.
Differential diagnosis
Bleeding is common in early pregnancy (for differential diagnosis, see table Some Causes of Vaginal Bleeding During Early Pregnancy).
Some Causes of Vaginal Bleeding During Early Pregnancy
Cause | Suggestive Findings | Diagnostic Approach* |
|---|---|---|
Obstetric disorders | ||
Vaginal bleeding with or without abdominal or pelvic pain (often sudden, localized, and constant, not crampy) Closed cervical os No fetal heart sounds Possible hemodynamic instability if ectopic pregnancy is ruptured Sometimes, a palpable adnexal mass | Quantitative beta-hCG measurement, repeated every 2 days if diagnosis is uncertain Complete blood count Pelvic ultrasonography Sometimes, endometrial sampling Laparoscopy or, if the patient is hemodynamically unstable, laparotomy | |
Threatened abortion | Vaginal bleeding with or without crampy abdominal pain Closed cervical os | Fetal heart rate auscultation Quantitative beta-hCG measurement Complete blood count Pelvic ultrasonography |
Inevitable abortion | Vaginal bleeding with crampy abdominal pain Open cervical os (dilated cervix) | Evaluation as for threatened abortion |
Incomplete abortion | Vaginal bleeding with crampy abdominal pain Open or closed cervical os Products of conception often seen or felt through os | Evaluation as for threatened abortion |
Complete abortion | Mild vaginal bleeding at presentation but usually a history of significant vaginal bleeding immediately preceding visit; sometimes, with mild, crampy abdominal pain Closed cervical os; uterus is nonpregnant size | Evaluation as for threatened abortion |
Usually, history of recent induced or spontaneous abortion (risk is higher if induced abortion is performed without appropriately trained clinicians and equipment or if self-induced) Fever, chills, constant abdominal or pelvic pain Vaginal bleeding and/or purulent vaginal discharge Uterine tenderness Open cervical os | Evaluation as for threatened abortion plus evaluation for STIs and vaginitis | |
Gestational trophoblastic disease (hydatidiform mole) | Vaginal bleeding, with or without crampy abdominal pain Larger-than-expected uterine size, often elevated blood pressure, severe vomiting If more advanced, sometimes passage of grapelike tissue from the vagina | Evaluation as for threatened abortion plus thyroid tests, creatinine, liver tests, chest x-ray |
Ruptured corpus luteum cyst | Localized abdominal pain, vaginal bleeding, sometimes nausea and vomiting Sudden onset of symptoms | Evaluation as for ectopic pregnancy |
Gynecologic or other disorders | ||
Trauma | History or suspicion of physical trauma (eg, motor vehicle accident, laceration of the cervix or vagina due to instrumentation or sexual assault, sometimes a complication of chorionic villus sampling or amniocentesis) | Complete blood count Pelvic ultrasonography (to evaluate fetus) Other imaging studies (to evaluate for injury or internal bleeding) Questions about possible intimate partner violence or sexual assault, if suspected |
Spotting or scant bleeding with vaginal discharge Sometimes, dyspareunia | Evaluation for vaginitis and STIs | |
Mucopurulent cervical discharge Sometimes, scant vaginal bleeding Sometimes, cervical motion tenderness, abdominal pain, or both | Evaluation for STIs and vaginitis | |
Scant vaginal bleeding, no pain Polypoid mass protruding from cervix | Pelvic examination Histology of specimen after biopsy or removal | |
Beta-hCG = | ||
* Evaluation of concerning symptoms in all pregnant patients should include assessment of maternal vital signs, physical examination, and evaluation of fetal status with fetal heart rate monitoring or ultrasonography. | ||
Pelvic pain or pressure is also a common pregnancy symptom (see table Some Causes of Pelvic Pain During Early Pregnancy for differential diagnosis).
Some Causes of Pelvic Pain During Early Pregnancy
Cause | Suggestive Findings | Diagnostic Approach* |
|---|---|---|
Obstetric disorders | ||
Normal changes of pregnancy, including those due to stretching and growth of the uterus and surrounding connective tissues | Crampy sensation or pressure in the lower abdomen, pelvis, lower back, or a combination Sometimes, with movement, sudden sharp pain (round ligament pain) | Routine prenatal evaluation with maternal vital signs, abdominal examination, sometimes pelvic examination, and fetal heart rate auscultation (depending on gestational age) Sometimes, pelvic ultrasonography Evaluation for ectopic pregnancy or other conditions, if suspected |
Abdominal or pelvic pain, which is often sudden, localized, and constant (not crampy), usually with vaginal bleeding Closed cervical os No fetal heart sounds Possibly hemodynamic instability if ectopic pregnancy has ruptured Sometimes, a palpable adnexal mass | Quantitative beta-hCG measurement, repeated every 2 days if diagnosis is uncertain Complete blood count Pelvic ultrasonography Sometimes, endometrial sampling Laparoscopy or, if the patient is hemodynamically unstable, laparotomy | |
Spontaneous abortion (threatened, inevitable, incomplete, complete, missed) | Crampy, diffuse, lower abdominal pain, often with vaginal bleeding Open or closed cervical os depending on the type of abortion (see table Some Causes of Vaginal Bleeding) | Fetal heart rate auscultation Quantitative beta-hCG measurement, repeated every 2 days if diagnosis is uncertain Complete blood count Pelvic ultrasonography |
Usually, history of recent induced or spontaneous abortion (risk is higher if induced abortion is performed without appropriately trained clinicians and equipment or if self-induced) Fever, chills, constant abdominal or pelvic pain Vaginal bleeding and/or purulent vaginal discharge Uterine tenderness Open cervical os | Evaluation as for spontaneous abortion plus evaluation for STIs and vaginitis | |
Gynecologic disorders | ||
Uterine fibroid degeneration | Sudden onset of pelvic pain, dull or sharp, usually severe, often with nausea, vomiting, and fever Sometimes, vaginal bleeding Uterine tenderness | Ultrasonography MRI (used only if diagnosis is uncertain) |
Sudden onset of localized pelvic pain, which may be severe and intermittent (if torsion spontaneously resolves) Often, nausea, vomiting | Doppler ultrasonography | |
Ruptured corpus luteum cyst | Localized abdominal or pelvic pain Sometimes, vaginal bleeding Usually, sudden onset | Ultrasonography Complete blood count |
Pelvic inflammatory disease (uncommon during pregnancy) | Purulent cervicovaginal discharge Significant cervical motion, uterine, and/or adnexal tenderness Often, fever and/or abnormal vaginal bleeding | Evaluation for STIs and vaginitis White blood cell count |
Benign or malignant ovarian tumor | Dull abdominal pain or pressure Sometimes, weight loss Sometimes, abdominal distension and ascites Sometimes, ovarian cancer risk factors | Ultrasonography Tumor markers Sometimes, diagnostic laparoscopy |
Ovarian hyperstimulation syndrome | Use of fertility medications for current pregnancy Dull abdominal pain or pressure If moderate or severe, weight gain, abdominal distension and ascites, acute kidney disease, pleural effusion, or disseminated intravascular coagulation | Ultrasonography Complete blood count Comprehensive metabolic panel |
Nongynecologic disorders | ||
Usually, continuous diffuse or localized abdominal pain, tenderness Possibly atypical location (eg, right upper quadrant) or qualities (milder, crampy, no peritoneal signs) compared with pain in nonpregnant patients; appendix may be in a different position due to enlarged uterus Sometimes, peritoneal signs Sometimes, nausea, vomiting, or loss of appetite | Pelvic/abdominal ultrasonography, followed by MRI if ultrasonography is inconclusive; consideration of CT if MRI is not readily available White blood cell count or C-reactive protein | |
Suprapubic discomfort, often with bladder symptoms (eg, burning, frequency, urgency) Sometimes, fever, chills, and/or flank pain (risk of pyelonephritis is increased in pregnancy) | Urinalysis and culture | |
Variable pains (crampy or constant) in no consistent location, often with diarrhea and sometimes with mucus or blood Sometimes, fever Usually, a known history of IBD | Sometimes, fecal calprotectin Sometimes, endoscopy | |
Acute nausea and vomiting, usually in patients who have had abdominal surgery, have an intraabdominal malignancy, or sometimes an incarcerated hernia detected during examination Colicky pain, vomiting, no bowel movements or flatus Distended, tympanitic abdomen Usually, history of abdominal surgery (causing adhesions), have an intraadominal malignancy, or sometimes an incarcerated hernia detected during examination May be caused by or occur in patients with appendicitis | Evaluation as for ectopic pregnancy Abdominal imaging with flat and upright x-rays, ultrasonography, and possibly CT (if x-ray and ultrasonography results are equivocal) | |
Usually, vomiting, diarrhea No peritoneal signs | Sometimes, stool tests (if bacterial or parasitic infection is suspected) | |
Beta-hCG = beta subunit of human chorionic gonadotropin; STIs = sexually transmitted infections. | ||
* Evaluation of concerning symptoms in all pregnant patients should include assessment of maternal vital signs, physical examination, and evaluation of fetal status with fetal heart rate monitoring or ultrasonography. | ||
Diagnosis reference
1. Doubilet PM, Benson CB, Bourne T, et al: Diagnostic criteria for nonviable pregnancy early in the first trimester. N Engl J Med 369(15):1443-1451, 2013. doi:10.1056/NEJMra1302417
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). 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.
1).
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 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.
Pain medications should be given, as appropriate. Rho(D) immune globulin is given if the pregnant patient is Rh-negative.
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
1. American College of Obstetricians and Gynecologists (ACOG): ACOG Practice Bulletin No. 200: Early pregnancy loss. Obstet Gynecol 132(5):e197–e207, 2018. doi:10.1097/AOG.0000000000002899
2. Zhang J, Gilles JM, Barnhart K, et al: A comparison of medical management with misoprostol and surgical management for early pregnancy failure. N Engl J Med 353(8):761-769, 2005. doi:10.1056/NEJMoa044064
3. Schreiber CA, Creinin MD, Atrio J, et al: Mifepristone pretreatment for the medical management of early pregnancy loss. N Engl J Med 378(23):2161-2170, 2018. doi:10.1056/NEJMoa1715726
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.
Often, uterine evacuation is not needed for complete abortions.
Provide emotional support to the parents.
