Clinical overview
Miscarriage — the spontaneous loss of a pregnancy before 24 weeks (UK/SA definition) or 20 weeks (US definition) — is the most common complication of early pregnancy. It affects approximately 15–20% of clinically recognised pregnancies; if biochemical losses are included, the figure rises to 30–40%. For the individual woman it is rarely "common" — it is loss, grief, and uncertainty. The registrar's job is therefore part medical (resuscitation when needed, accurate diagnosis, safe evacuation), part counselling (validating loss, navigating future fertility), and part systemic (recognising recurrent miscarriage that needs workup, distinguishing miscarriage from ectopic, knowing when to refer).
The chapter covers definitions, classification by type, assessment, ultrasound diagnostic criteria, the three management options (expectant, medical, surgical), counselling, anti-D in Rh-negative women, and indications for recurrent miscarriage workup. The South African context — limited early pregnancy unit access in some districts, anti-D supply considerations, integration with the Choice on Termination of Pregnancy Act services — is woven through.
Core knowledge
Definitions and classification
Classification turns on cervical status, viability, retained tissue, and whether products have passed.
- Threatened miscarriage: vaginal bleeding before 24 weeks with a closed cervix; viable pregnancy on ultrasound.
- Inevitable miscarriage: bleeding + cramping with open cervix; pregnancy not yet expelled.
- Incomplete miscarriage: some products passed, some retained; open cervix; ongoing bleeding.
- Complete miscarriage: all products passed; closed cervix; uterus empty on ultrasound.
- Missed (delayed) miscarriage: non-viable pregnancy retained in utero without symptoms; diagnosed on ultrasound.
- Septic miscarriage: any of the above complicated by infection; usually associated with unsafe termination, retained products, or instrumentation.
- Recurrent miscarriage: ≥3 consecutive losses (UK historical) or ≥2 losses (newer ESHRE/ASRM definitions, especially with maternal age ≥35).
- Biochemical pregnancy: β-hCG positive but pregnancy never visualised on ultrasound.
Aetiology
The cause is most often identified only in recurrent loss; for single losses ~50–60% are due to chromosomal abnormalities of the conceptus (especially trisomy 16). Other causes:
- Chromosomal — trisomies (16 most common), monosomy X (45,X — usually first trimester loss), triploidy, structural abnormalities, parental balanced translocations.
- Maternal anatomical — septate uterus, fibroids (submucosal especially), intrauterine adhesions (Asherman's), cervical insufficiency (more common in second trimester loss).
- Endocrine — uncontrolled diabetes (especially in first trimester), thyroid disease, prolactinoma, severe PCOS.
- Thrombophilic — antiphospholipid syndrome (most evidence-based; lupus anticoagulant, anticardiolipin antibodies, anti-β2-glycoprotein I); inherited thrombophilias less consistently associated.
- Infectious — uncommonly causal in sporadic loss; syphilis, parvovirus B19, TORCH; bacterial vaginosis associated with second trimester loss.
- Immunological — beyond APS, evidence weak.
- Environmental — smoking, heavy alcohol, cocaine, lead, mercury.
- Maternal age — major risk factor. Loss rate ~10% at age 20, rising to ~50% at age 40+, ~80% at age 45+.