eMedicine Specialties > Emergency Medicine > Obstetrics & Gynecology
Abortion, Inevitable
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 abortion is categorized as threatened, inevitable, incomplete, complete, or missed. Spontaneous abortion can be further classified as sporadic or recurrent. Inevitable abortion is defined as bleeding of intrauterine origin with continuous and progressive dilation of the cervix but without expulsion of conception products before the 20th week of gestation.
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. Spontaneous abortion occurs in an estimated 10-15% of pregnancies.
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 that more black mothers died after ectopic pregnancies and abortions, both spontaneous (14%) and induced (7%), than white mothers (8% and 4%, respectively).
Age
- Age and increased parity affect the risk of a miscarriage. Twelve percent of pregnancies terminate in miscarriage in women younger than 20 years; frequency increases to 26% in women older than 20 years.
- 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, and the number of miscarriages and chromosomal anomalies decreases. This phenomenon suggests that the uterus is not responsible for poor outcomes in women of advanced reproductive age.
Clinical
History
- Inevitable and incomplete miscarriages present in a similar clinical fashion and have similar treatment. The patient history should include the following:
- Last menstrual period (LMP)
- Estimated length of gestation
- Ultrasound results, if previously performed
- Bleeding
- Degree
- Duration
- Presence or passage of tissue
- Bleeding may be roughly quantified by the number of pads soaked per hour or day. An average pad absorbs approximately 20-30 mL of blood.
- Previous spontaneous or elective abortions
Physical
- Vital signs should be within reference ranges unless infection is present or hemorrhage has caused hypovolemia. Preexisting anemia may make a patient more susceptible to hypovolemic shock.
- Uterine contractions may cause intermittent, progressive abdominal cramping that produces cervical effacement and dilation.
- The cervix is effaced and dilated on pelvic examination. The amniotic sac may be seen bulging through the cervix, or it may be ruptured. Amniotic fluid may be present in the vagina. The uterus is enlarged and soft on bimanual examination.
Causes
- Genetic factors account for approximately 5% of spontaneous abortions. One meta-analysis found that a chromosomal abnormality occurs in 49% of spontaneous abortions. Autosomal trisomy was the most commonly identified anomaly followed by polyploidy and monosomy X.
- Anatomic: Congenital or acquired anatomic factors are reported to occur in 10-15% of women with recurrent spontaneous abortion.
- Congenital anatomic lesions include müllerian duct anomalies (eg, septate uterus, diethylstilbestrol [DES]-related). 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 (synechiae), leiomyoma, and endometriosis.
- 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 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 may contribute to as many as 60% of recurrent spontaneous abortions.
- Both the developing embryo and trophoblast may be considered immunologically foreign to the maternal immune system.
- Antiphospholipid antibody syndrome generally is responsible for more second-trimester pregnancy loss than first-trimester loss.
- Miscellaneous
- Miscellaneous factors may 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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Further Reading
Keywords
miscarriage, spontaneous abortion, inevitable abortion, intrauterine bleeding
