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Abortion, Missed
Updated: Jun 15, 2006
Introduction
Background
The most common complication of pregnancy is spontaneous abortion. Spontaneous abortion is categorized as threatened, inevitable, incomplete, complete, or missed. Abortion can be categorized further as sporadic or recurrent. By definition, a missed abortion is in utero death of the embryo or fetus before the 20th week of gestation with retained products of conception. Missed abortions also may be referred to as blighted ovum, anembryonic pregnancy, or fetal demise.
Pathophysiology
The timing of a spontaneous abortion suggests its pathophysiology. Genetic anomalies (trisomies); hormonal abnormalities; and infectious, immunologic, and environmental factors usually result in first-trimester loss. Anatomic factors usually are associated with second-trimester loss.
Frequency
United States
Many pregnancies are not viable, with an estimated loss of 50% before the first missed menstrual period. These pregnancies usually are not clinically recognized. Classic spontaneous abortion is defined as a clinically recognized (ie, by blood test, ultrasound) pregnancy loss before the 20th week of gestation. Estimates place frequency at 10-15% of pregnancies.
International
A report from the United Kingdom by Pandya utilizing ultrasound screening at 10-13 weeks of gestation revealed 2.8% of pregnancy failure with 62.5% missed abortions and 37.5% anembryonic pregnancies. The prevalence was higher in women with a history of vaginal bleeding.
Mortality/Morbidity
Surveillance data of pregnancy-related deaths from 1987 through 1990 revealed a total of 1459 deaths in the US. Of these deaths, spontaneous and induced abortions accounted for 5.6%.
Race
Surveillance data for pregnancy-related deaths (1987-1990) demonstrated more deaths followed 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 showed 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 rates 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
- The patient history should include the following:
- Last menstrual period (LMP)
- Estimated length of gestation
- Ultrasound results, if previously performed (especially presence of fetal cardiac activity)
- 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.
- The patient's pregnancy symptoms may regress. Pregnancy test results may become negative and fetal heartbeat may not be detected.
Physical
- Vital signs usually are within reference ranges. Rarely, ecchymosis is noted on the skin in cases of associated coagulation disorder.
- Abdominal examination may or may not reveal a palpable uterus. If palpable, the uterus usually is small for the presumed gestational age.
- Fetal heart tones are inaudible or unseen on ultrasound.
- The cervical os is closed upon pelvic examination. The uterus may feel soft and enlarged.
Causes
- Genetic factors account for approximately 5% of spontaneous abortions. Trisomies commonly are encountered, with trisomy 16 accounting for approximately a third of chromosomal abnormalities in early pregnancy.
- Anatomic: Congenital or acquired anatomic factors reportedly occur in 10-15% of women who have histories of recurrent spontaneous abortions.
- Congenital anatomic lesions include müllerian duct anomalies (eg, septate uterus, diethylstilbestrol [DES]-related). A septate uterus has been associated with some cases of missed abortion.
- Acquired lesions include intrauterine adhesions (synechiae), leiomyoma, and endometriosis.
- Endocrine factors potentially contribute to recurrent abortion in 10-20% of cases.
- Luteal phase insufficiency (abnormal corpus luteum function with insufficient progesterone production) is implicated as the most common etiologic factor in endocrine abnormalities contributing to spontaneous abortion.
- Hypothyroidism, hypoprolactinemia, poor diabetic control, and polycystic ovarian syndrome are recognized contributing factors to pregnancy loss.
- Infectious
- A presumed infectious etiology may be found in 5% of cases.
- Bacterial, viral, parasitic, fungal, and zoonotic infections are associated with recurrent spontaneous abortion.
- Immunologic
- Immunologic factors contribute in as many as 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
- Miscellaneous factors account for as many as 3% of recurrent spontaneous abortions.
- Many other contributing factors are implicated in sporadic and recurrent spontaneous abortions. Environment, drugs, placental abnormalities, medical illnesses, and male-related causes are noted.
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References
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Further Reading
Keywords
miscarriage, blighted ovum, anembryonic pregnancy, fetal demise, spontaneous abortion, missed abortion, threatened abortion, complete abortion, incomplete abortion, inevitable abortion, pregnancy loss, utero death of the embryo, utero death of the fetus, chromosomal anomalies, septate uterus, luteal phase insufficiency, hypothyroidism, hypoprolactinemia, polycystic ovarian syndrome, anembryonic pregnancy, subchorionic hematoma, subchorionic hemorrhage, subchorionic bleeding, endovaginal ultrasound, transabdominal ultrasound
