Spontaneous abortion
Spontaneous abortion is loss of an intrauterine gestation before 20 weeks, classified by cervical os status and ultrasonographic findings into threatened, inevitable, incomplete, complete, missed, and septic subtypes. Diagnosis rests on transvaginal ultrasonography plus serial beta-hCG, and management ranges from expectant care to uterine evacuation, with septic abortion treated as a surgical and antibiotic emergency.
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What this article covers
- Overview
Definition: spontaneous abortion (miscarriage) is loss of an intrauterine gestation before 20 weeks gestation, or expulsion of an embryo/fetus weighing less than 500 g.
- Epidemiology
Overall frequency: spontaneous abortion is the most common complication of early pregnancy; more than 80% of cases occur in the first trimester.
- Risk factors
Advanced maternal age: older maternal age is associated with a higher rate of fetal chromosomal abnormality and therefore loss.
- Pathophysiology
Chromosomal abnormality drives early loss: most first-trimester losses follow a nonviable fetal karyotype, so the pregnancy fails before or shortly after implantation is confirmed.
- Clinical features
Vaginal bleeding with cramping is the presenting pattern for every symptomatic subtype: uterine bleeding with lower abdominal cramping before 20 weeks gestation is the complaint that prompts evaluation.
- Differential diagnosis
Ectopic pregnancy: pain and bleeding but no intrauterine gestational sac once beta-hCG exceeds the discriminatory range, and failure of beta-hCG to double every 48 hours, unlike a normally progressing intrauterine pregnancy.
- Diagnosis
Diagnosis rests on explicit nonviability criteria on transvaginal ultrasonography, supported by cervical exam: a nonviable pregnancy is confirmed when the gestational sac measures more than 25 mm in…
- Management
First, examine the cervical os and assess hemodynamic stability, since instability or infection signs bypass expectant options and go straight to emergent evacuation with antibiotics.
- Complications
Septic abortion progressing to septic shock: maternal mortality reaches 10-15% if infected retained tissue is not promptly evacuated and treated.
- Prognosis
Most threatened abortions continue to term: in the majority of cases, bleeding stops and the pregnancy remains viable.
- Prevention
Rho(D) immune globulin prevents alloimmunization: 50 mcg IM at or before 12 weeks, 300 mcg IM after 12 weeks, within 72 hours of any spontaneous or induced abortion in an Rh-negative, unsensitized patient.
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