Spontaneous abortion, by definition, is death of the fetus. 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.
Fetal death and early delivery are classified as follows:
Spontaneous abortion: Death of the fetus, sometimes with passage of products of conception (fetus and placenta), before 20 weeks gestation
Preterm delivery Preterm Labor Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more : Delivery of a live fetus between 20 weeks and 36 weeks/6 days
Abortions may be classified as follows (see table Classification of Abortion Classification of Abortion ):
Early or late
Threatened or inevitable
Incomplete or complete
About 10 to 15% of confirmed pregnancies spontaneously abort (1 Reference Spontaneous abortion is pregnancy loss before 20 weeks gestation. Threatened abortion is vaginal bleeding without cervical dilation before 20 weeks in a confirmed viable intrauterine pregnancy... read more ). As many as 25% of all pregnancies end in a spontaneous abortion during the first 12 weeks of pregnancy. Incidence in all pregnancies is probably higher because some very early abortions are mistaken for a late menstrual period.
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
Etiology of Spontaneous Abortion
Early spontaneous abortion is often caused by chromosomal abnormalities Overview of Chromosomal Anomalies Chromosomal anomalies cause various disorders. Anomalies that affect autosomes (the 22 paired chromosomes that are alike in males and females) are more common than those that affect sex chromosomes... 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 viruses—most notably cytomegalovirus, herpesvirus, parvovirus, and rubella virus. Other causes include immunologic abnormalities and major trauma. Most often, the cause is unknown.
Risk factors for spontaneous abortion include
Age > 35
History of spontaneous abortion
Use of certain drugs (eg, cocaine Social and Illicit Drugs During Pregnancy , alcohol) Social and Illicit Drugs During Pregnancy
A poorly controlled chronic disorder (eg, diabetes Diabetes Mellitus in Pregnancy Pregnancy aggravates preexisting type 1 (insulin-dependent) and type 2 (non–insulin-dependent) diabetes but does not appear to exacerbate diabetic retinopathy, nephropathy, or neuropathy ( 1)... read more , hypertension Hypertension in Pregnancy Recommendations regarding classification, diagnosis, and management of hypertensive disorders (including preeclampsia) are available from the American College of Obstetricians and Gynecologists... read more , overt thyroid disorders Thyroid Disorders in Pregnancy Thyroid disorders may predate or develop during pregnancy. Pregnancy does not change the symptoms of hypothyroidism and hyperthyroidism. Fetal effects vary with the disorder and the drugs used... read more ) in the mother
Subclinical thyroid disorders, a retroverted uterus, and minor trauma have not been shown to cause spontaneous abortions.
Symptoms and Signs of Spontaneous Abortion
Symptoms of spontaneous abortion include crampy pelvic pain, uterine 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, 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 abortions usually result from use of nonsterile techniques for uterine... read more ).
Diagnosis of Spontaneous Abortion
Usually ultrasonography and quantitative beta subunit of human chorionic gonadotropin (beta-hCG)
Pregnancy is diagnosed with a urine or blood beta-hCG test. Ultrasonography is done 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 may be required. If cardiac activity is absent and had been detected previously during this pregnancy, fetal death is diagnosed. Alternatively, serial beta-hCG levels that decrease across ≤ 3 measurements are consistent with a failed pregnancy.
Assessment is also done to determine the status of the abortion process 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 Characteristic Symptoms and Signs in Spontaneous Abortions ).
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
An anembryonic pregnancy refers to a gestational sac with no yolk sac or embryo, seen on ultrasound, in a nonviable pregnancy.
For recurrent pregnancy loss Recurrent Pregnancy Loss Recurrent pregnancy loss is ≥ 2 to 3 spontaneous abortions. Determining the cause may require extensive evaluation of both parents. Some causes can be treated. Causes of recurrent pregnancy... read more , testing to determine the cause of abortion is necessary.
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
Sometimes pain medication
For threatened abortion, treatment is observation, but health care practitioners may periodically evaluate the woman's symptoms or do ultrasonography. 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. For patients managed expectantly, evacuation is done if excessive bleeding or infection occur or if the products of conception do not pass after about 2 to 4 weeks.
At < 12 weeks, evacuation may be done with suction curettage Instrumental evacuation In the US, 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 US, abortion of... read more or medical management. For medical evacuation, misoprostol (800 mcg intravaginally) is given; if there is no response to the first dose, one additional dose may be given at least 3 hours after first dose and typically within 7 days (1 Treatment reference Spontaneous abortion is pregnancy loss before 20 weeks gestation. Threatened abortion is vaginal bleeding without cervical dilation before 20 weeks in a confirmed viable intrauterine pregnancy... read more ). A dose of mifepristone (200 mg orally) 24 hours before misoprostol administration should be considered if available.
Evacuation is typically done with dilation and evacuation Instrumental evacuation at 12 to 23 weeks or medication induction Induced Abortion In the US, 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 US, abortion of... read more at > 16 to 23 weeks (eg, with misoprostol or mifepristone). For dilation and evacuation, the later the gestational age, 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) or by medical induction.
If complete abortion is suspected, uterine evacuation is not done routinely. Uterine evacuation can be done 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 Prevention Hemolytic disease of the fetus and neonate is hemolytic anemia in the fetus (or neonate, as erythroblastosis neonatorum) caused by transplacental transmission of maternal antibodies to fetal... read more is given if the mother 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.
1. American College of Obstetricians and Gynecologists (ACOG): ACOG Practice Bulletin No. 200: Early pregnancy loss. Obstet Gynecol 132(5):e197–e207, 2018.
Spontaneous abortion is pregnancy loss before 20 weeks gestation; it probably occurs in up to 20% of 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 threatened and complete abortions.
Provide emotional support to the parents.
Drugs Mentioned In This Article
|Drug Name||Select Trade|
human chorionic gonadotropin
|Novarel, Ovidrel, Pregnyl|