eMedicine Specialties > Emergency Medicine > Obstetrics & Gynecology
Abortion, Incomplete
Updated: May 30, 2006
Introduction
Background
The most common complication of pregnancy is spontaneous abortion, which occurs in an estimated 10-15% of pregnancies. Spontaneous abortions are categorized as threatened, inevitable, incomplete, complete, or missed. Spontaneous abortions can be classified further as sporadic or recurrent. By definition, an incomplete abortion is the partial expulsion of the products of conception before the 20th week of gestation.
Pathophysiology
The timing of miscarriage suggests the pathophysiology of a spontaneous abortion. Genetic anomalies (eg, trisomies); hormonal abnormalities; and infectious, immunologic, and environmental factors usually result in first-trimester pregnancy loss. Anatomic factors usually are associated with second-trimester pregnancy loss. Factor XIII deficiency and a complete or partial deficiency of fibrinogen are associated with recurrent spontaneous abortions.
Frequency
United States
Many pregnancies are not viable. According to estimates, 50% of pregnancies terminate spontaneously before the first missed menstrual period; these abortions usually are not clinically recognized. Spontaneous abortion typically is defined as a clinically recognized (ie, by blood test or ultrasound) pregnancy loss before 20 weeks' gestation.
Mortality/Morbidity
Surveillance data from 1987 through 1990 reveal a total of 1459 pregnancy-related deaths in the US. Spontaneous and induced abortions accounted for 5.6% of these deaths.
Race
Surveillance data for pregnancy-related deaths from 1987 through 1990 demonstrate more deaths due to ectopic pregnancy and spontaneous and induced abortion among African American women than among Caucasian women. Fourteen percent of pregnancy-related deaths among black women were due to ectopic pregnancies; 7% were due to abortions. Among white women, data show that 8% of pregnancy-related deaths were due to ectopic pregnancies; 4% were due to abortions.
Age
- Age and increased parity affect a woman's risk of miscarriage. In women younger than 20 years, miscarriage occurs in an estimated 12% of pregnancies. In women older than 20 years, miscarriage occurs in an estimated 26% of pregnancies.
- Age primarily affects the oocyte. When oocytes from young women are used to create embryos for transfer to older recipients, implantation and pregnancy rates mimic those seen in younger women. The number of miscarriages and chromosomal anomalies decreases, suggesting that the uterus is not responsible for poor outcomes in women of advanced reproductive age.
Clinical
History
Although classified as different entities, incomplete and inevitable miscarriages present in a similar clinical fashion and have similar treatment. An inevitable abortion involves continuous and progressive dilation of the cervix without expulsion of the products of conception before the 20th week of gestation.
- The patient history should include the following:
- Last menstrual period (LMP)
- Estimated length of gestation
- Ultrasound results, if previously performed
- Bleeding (eg, degree, duration, presence/passage of tissue): Bleeding may be quantified roughly by the number of pads soaked per hour or day. An average pad absorbs approximately 20-30 mL of blood.
Physical
- Vital signs should be within reference ranges unless infection is present or hemorrhage has caused hypovolemia.
- The abdomen usually is soft and nontender.
- On pelvic examination, products of conception may be partially present in the uterus, may protrude from the external os, or may be present in the vagina. Bleeding and cramping usually persist.
- The cervix appears dilated and effaced.
- Bimanual examination reveals an enlarged and soft uterus.
Causes
- Genetic factors
- Approximately 5% of spontaneous abortions occur because of genetic factors.
- Trisomy chromosomes commonly are encountered, with trisomy 16 accounting for approximately a third of chromosomal abnormalities in early pregnancy.
- Anatomic factors: Congenital or acquired anatomic factors are reported to occur in 10-15% of women who have recurrent spontaneous abortions.
- Congenital anatomic lesions include müllerian duct anomalies (eg, septate uterus, diethylstilbestrol [DES]-related anomalies). Müllerian duct lesions usually are found in second-trimester pregnancy loss.
- Anomalies of the uterine artery with compromised endometrial blood flow are congenital.
- Acquired lesions include intrauterine adhesions (ie, synechiae), leiomyoma, and endometriosis.
- Endocrine factors
- Endocrine factors potentially contribute to recurrent abortion in 10-20% of cases.
- Luteal phase insufficiency (ie, abnormal corpus luteum function with insufficient progesterone production) is implicated as the most common endocrine abnormality contributing to spontaneous abortion.
- Hypothyroidism, hypoprolactinemia, poor diabetic control, and polycystic ovarian syndrome are contributive factors in pregnancy loss.
- Infectious factors
- Presumed infectious etiology may be found in 5% of cases.
- Bacterial, viral, parasitic, fungal, and zoonotic infections are associated with recurrent spontaneous abortion.
- Immunologic factors
- Immunologic factors may contribute in up to 60% of recurrent spontaneous abortions.
- Both the developing embryo and the trophoblast may be considered immunologically foreign to the maternal immune system.
- Antiphospholipid antibody syndrome generally is responsible for more second-trimester pregnancy losses than first-trimester losses.
- Miscellaneous factors
- Miscellaneous factors may account for up to 3% of recurrent spontaneous abortions.
- Other contributing factors implicated in sporadic and recurrent spontaneous abortions include environment, drugs, placental abnormalities, medical illnesses, and male-related causes.
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References
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Further Reading
Keywords
miscarriage, spontaneous abortion, incomplete abortion, pregnancy loss, threatened abortion, inevitable abortion, complete abortion, missed abortion
