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
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 : Passage 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
Recurrent (also called recurrent pregnancy loss Recurrent Pregnancy Loss (Recurrent or Habitual Abortion) 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... read more )
Missed
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.
Etiology of Spontaneous Abortion
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 Recurrent Pregnancy Loss (Recurrent or Habitual Abortion) 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... read more (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
Age > 35
History of spontaneous abortion
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, 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 Septic Abortion Septic abortion is serious uterine infection during or shortly before or after an abortion. Septic abortions usually result from induced abortions done by untrained practitioners using nonsterile... read more ).
Diagnosis of Spontaneous 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 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.
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 Recurrent Pregnancy Loss (Recurrent or Habitual Abortion) 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... read more , testing to determine the cause of abortion is necessary.
Treatment of Spontaneous Abortion
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 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 at < 12 weeks, dilation and evacuation Instrumental evacuation at 12 to 23 weeks, or medical 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). 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)
Etiology of Recurrent Pregnancy Loss
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 Thromboembolic Disorders in Pregnancy In the US, thromboembolic disorders— deep venous thrombosis (DVT) or pulmonary embolism (PE)—are a leading cause of maternal mortality. During pregnancy, risk is increased because Venous capacitance... read more (eg, related to antiphospholipid antibody syndrome Antiphospholipid Antibody Syndrome (APS) Antiphospholipid antibody syndrome is an autoimmune disorder in which patients have autoantibodies to phospholipid-bound proteins. Venous or arterial thrombi may occur. The pathophysiology is... read more 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 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 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.
Diagnosis of Recurrent Pregnancy Loss
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 Genetic Evaluation Genetic evaluation is part of routine prenatal care and is ideally done before conception. The extent of genetic evaluation a woman chooses is related to how the woman weighs factors such as... read more
(karyotyping) of both parents and any products of conception as clinically indicated to exclude possible genetic causesScreening 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 Recurrent Pregnancy Loss
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.
