summary
Miscarriage is the most common complication of early pregnancy, with causes ranging from chromosomal abnormalities to maternal and environmental factors. Diagnosis relies on clinical assessment and ultrasound. Management may be expectant, medical, or surgical, with comparable safety profiles but differing risks and benefits. Individualised care, emotional support, and appropriate follow-up are essential, alongside anti-D prophylaxis in Rh-negative women.
Definition and Epidemiology
A miscarriage, or spontaneous abortion, is defined as the spontaneous loss of a pregnancy before fetal viability. In the UK, this is considered at <24 weeks’ gestation, though many international definitions use <20 weeks or fetal weight <500g. Early miscarriage occurs in the first trimester (<12–13 weeks) and is more common than late miscarriage (13–24 weeks). Miscarriage affects 10–25% of clinically recognized pregnancies, with the majority occurring before 12 weeks. Approximately half of early pregnancy losses are due to chromosomal abnormalities.
Etiology and Risk Factors
The causes of miscarriage are multifactorial and include:
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Fetal/Placental: Chromosomal abnormalities (trisomies, monosomy X, polyploidy), congenital anomalies, anembryonic pregnancy.
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Maternal: Advanced maternal age (>30–35 years), uterine anomalies (e.g., septate uterus, fibroids, adhesions), cervical incompetence, endocrine disorders (diabetes, thyroid disease), systemic diseases (SLE, coagulopathies, antiphospholipid syndrome).
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Lifestyle/Environmental: Smoking, obesity, trauma, infection, toxins, and iatrogenic causes (e.g., invasive procedures).
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Other: Previous miscarriage, previous uterine surgery, maternal or paternal chromosomal rearrangements.
Clinical Presentation
The hallmark symptom is vaginal bleeding, often with passage of clots or tissue, accompanied by suprapubic cramping pain similar to dysmenorrhoea. Some cases are asymptomatic and diagnosed incidentally on ultrasound.
Severe bleeding may cause haemodynamic instability (tachycardia, hypotension, pallor, dizziness, shortness of breath).
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Examination findings:
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Speculum: products of conception (POC) or cervical bleeding.
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Bimanual: uterine tenderness, adnexal masses (exclude ectopic).
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Abdominal: tenderness, distension.
Differential Diagnosis
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Ectopic pregnancy
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Molar pregnancy (hydatidiform mole)
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Cervical/uterine malignancy
Investigations
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Ultrasound (TVUS is gold standard):
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Viability is confirmed by fetal cardiac activity (detectable at 5½–6 weeks).
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CRL ≥7 mm without heartbeat → non-viable pregnancy (confirmation with repeat scan in 7 days).
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MSD ≥25 mm without embryo → failed pregnancy.
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Laboratory tests:
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β-hCG (serial values useful in ectopic suspicion but not for diagnosing miscarriage).
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Full blood count, blood group & Rh status.
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CRP and swabs if infection is suspected.
Classification of Miscarriage
|
Type |
Clinical Features |
Ultrasound Findings |
Cervical Os |
Management |
|
Threatened |
Vaginal bleeding ± mild pain; pregnancy symptoms often persist |
Viable intrauterine pregnancy with fetal cardiac activity |
Closed |
Expectant management, reassurance; anti-D if >12 wks & Rh-negative |
|
Inevitable |
Heavy bleeding, cramping pain; passage of clots; haemodynamic risk |
Intrauterine pregnancy (fetal cardiac activity may or may not be) |
Open |
Admit/observe if heavy bleeding; expectant, medical, or surgical options |
|
Missed |
Often asymptomatic or light bleeding; pregnancy symptoms regress |
No fetal cardiac activity with CRL ≥7 mm or MSD ≥25 mm without embryo |
Closed |
Expectant, medical (misoprostol ± mifepristone), or surgical evacuation |
|
Incomplete |
Vaginal bleeding, abdominal pain; partial passage of tissue/POC |
Retained POC; thickened endometrium (>15 mm) |
Open |
Expectant, medical, or surgical evacuation; anti-D if >12 wks & Rh-negative |
|
Complete |
History of bleeding and tissue passage; pain and bleeding settle |
Empty uterus, thin endometrium (<15 mm), prior confirmed pregnancy |
Closed/closing |
No further treatment; discharge, follow-up with GP; anti-D if >12 wks |
|
Septic |
Fever, rigors, pelvic pain, foul discharge; systemic features of sepsis |
Retained/infected POC possible |
Open or variable |
IV antibiotics, fluids, surgical evacuation; anti-D if >12 wks |
Notes:
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POC = Products of conception.
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Rh(D)-negative women need anti-D prophylaxis if >12 weeks or after surgical management at any gestation.
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Threatened miscarriage may progress to complete or incomplete miscarriage but up to 50% continue to term.
Management
Choice of management depends on clinical stability, gestational age, patient preference, and complications. All Rh(D)-negative women require anti-D prophylaxis after 12 weeks’ gestation, and after surgical management at any gestation.
1. Expectant (Conservative)
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Natural passage of POC over days to weeks.
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Advantages: avoids intervention, can be managed at home.
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Disadvantages: unpredictable, risk of heavy bleeding or infection, may fail and require further treatment.
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Contraindications: haemodynamic instability, coagulopathy, infection.
2. Medical
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Vaginal misoprostol (± mifepristone pretreatment) induces uterine contractions.
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Advantages: avoids surgery, can be outpatient.
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Disadvantages: side effects (pain, bleeding, GI upset), possible need for surgical evacuation.
3. Surgical
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Vacuum aspiration (<12 weeks) or evacuation of retained products (ERPC).
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Indications: haemodynamic instability, infected tissue, trophoblastic disease, patient preference.
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Advantages: rapid, definitive.
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Risks: anaesthetic complications, uterine perforation, haemorrhage, intrauterine adhesions (Asherman’s syndrome).
Complications
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Haemorrhage
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Infection (septic miscarriage, endometritis)
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Retained products of conception
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Disseminated intravascular coagulation (rare, especially with prolonged missed miscarriage)
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Intrauterine adhesions (after surgical evacuation)
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