Miscarriage — Causes, Symptoms, Diagnosis & Management Guide — Symptoms, Causes & Treatment | MyMedicPlus

Miscarriage (spontaneous abortion) is the unintentional loss of a pregnancy before 20 weeks gestation. It occurs in 10-20% of recognized pregnancies and up to 50% including unrecognized chemical pregnancies. Over 80% occur in the first trimester. It is the most common complication of early pregnancy and affects women of all ages and backgrounds. Miscarriage (spontaneous abortion) is defined as the unintentional loss of an intrauterine pregnancy before 24 weeks gestation (UK), or before 20 weeks gestation (USA). It is the most common complication of early pregnancy, occurring in approximately 10-15% of clinically recognised pregnancies and up to 30-50% of all conceptions including unrecognised biochemical pregnancies. The vast majority (over 80%) of miscarriages occur in the first trimester (before 13 weeks), predominantly in the embryonic period (before 10 weeks). Miscarriage classification includes: threatened miscarriage (bleeding with viable pregnancy on ultrasound), inevitable miscarriage (cervical dilation with pregnancy no longer viable), incomplete miscarriage (partial expulsion with retained products), complete miscarriage (all products expelled), missed miscarriage (embryonic death without symptoms — discovered on ultrasound), and septic miscarriage (infection of retained products of conception). Recurrent pregnancy loss (RPL) is defined as two or more consecutive pregnancy losses and affects 1-2% of couples.

Chromosomal abnormalities in the embryo account for 50-60% of first trimester miscarriages. Other causes include advanced maternal age (risk rises to 40% after age 40), uterine abnormalities (fibroids, septum), antiphospholipid syndrome, thrombophilia, poorly controlled diabetes or thyroid disease, infections, and smoking. Most cases in otherwise healthy women have no identifiable correctable cause. Chromosomal abnormalities of the embryo account for 50-75% of first trimester miscarriages — specifically trisomies (most common — trisomy 16 alone accounts for 30% of chromosomal miscarriages), monosomy X (45X), and polyploidy. These chromosomal errors occur as random de novo mutations during gametogenesis — increasing with advancing maternal age (risk of chromosomal miscarriage rises from 10% at age 30 to over 50% at age 42). Uterine anatomical abnormalities contributing to recurrent miscarriage include: uterine septum (most common, associated with 60-70% first and second trimester miscarriage rate), fibroids (submucous fibroids within the endometrial cavity most significant), and Asherman's syndrome (intrauterine adhesions from previous curettage). Antiphospholipid syndrome (APS) — the most important treatable cause of recurrent miscarriage — causes placental thrombosis and inflammation; diagnosed by persistent anticardiolipin antibodies, anti-beta2-glycoprotein I antibodies, or lupus anticoagulant on two occasions 12 weeks apart.

Vaginal bleeding (ranging from light spotting to heavy bleeding), lower abdominal cramping or pain, passage of tissue or clots, and sudden resolution of pregnancy symptoms (nausea, breast tenderness). Some miscarriages are discovered on routine ultrasound with no symptoms (missed miscarriage). Ectopic pregnancy presents similarly but requires urgent exclusion. Threatened miscarriage presents with vaginal bleeding (ranging from light spotting to moderate bleeding) often with or without mild cramping, in the context of a viable-appearing pregnancy on ultrasound — 50% of threatened miscarriages resolve with the pregnancy continuing to term. Inevitable or incomplete miscarriage causes heavier bleeding, moderate-to-severe lower abdominal cramping, and passage of tissue or clots with or without visible fetal parts. Sudden resolution of pregnancy symptoms (nausea, breast tenderness) may accompany miscarriage but is an unreliable indicator alone. Septic miscarriage — from ascending infection of retained products — causes fever above 38°C, purulent or offensive vaginal discharge, uterine tenderness, and signs of systemic sepsis. Ectopic pregnancy must be excluded in any woman of reproductive age with bleeding and pain before 10 weeks gestation — symptoms include unilateral pelvic pain, shoulder-tip pain (diaphragmatic irritation from haemoperitoneum — suggesting rupture), and haemodynamic instability.

Transvaginal ultrasound is the gold standard, assessing fetal cardiac activity and gestational sac integrity. Serial serum beta-hCG measurements every 48 hours track pregnancy viability — failing to double suggests pregnancy failure. Complete blood count detects anemia from blood loss. Blood group and Rhesus type determine the need for anti-D immunoglobulin in Rh-negative women. Transvaginal ultrasound (TVUS) is the gold-standard investigation: findings include embryonic demise (CRL above 7 mm without cardiac activity — called missed or blighted ovum), empty gestational sac (MSD above 25 mm without yolk sac or embryo), or incomplete miscarriage with retained products of conception (echogenic material within the uterine cavity). Serial serum beta-hCG measurements every 48 hours confirm viability — in a normal viable intrauterine pregnancy, beta-hCG doubles approximately every 48 hours in early pregnancy; failure to double by less than 66% suggests impending pregnancy failure or ectopic pregnancy. Beta-hCG alone cannot differentiate ectopic from intrauterine pregnancy — ultrasound is essential. Blood group and Rh(D) testing determines anti-D immunoglobulin need in Rh(D)-negative women. Full blood count identifies anaemia from blood loss.

Three management options are offered. Expectant management: await natural completion (complete in 2-6 weeks in 80% of cases). Medical management: misoprostol (prostaglandin) administered vaginally or sublingually accelerates expulsion, completing in 1-2 weeks in 80-90%. Surgical management: manual vacuum aspiration (MVA) or electric vacuum aspiration (ERPC) provides definitive treatment within hours. All options are equally safe; choice depends on patient preference and clinical circumstances. Expectant management — awaiting spontaneous expulsion — is appropriate for incomplete or missed miscarriage: complete miscarriage occurs in 80% within 2 weeks; requires follow-up ultrasound to confirm completion. Medical management with misoprostol 800 mcg vaginally (or 400 mcg sublingually) achieves complete expulsion in 80-90% within 1-2 weeks; a second dose may be given if incomplete at 48 hours. Surgical management — manual vacuum aspiration (MVA) under local or general anaesthesia, or electric vacuum aspiration (ERPC — evacuation of retained products of conception) — achieves complete evacuation in a single procedure and is preferred when there is heavy bleeding, infection, failed medical management, or patient preference. Anti-D immunoglobulin 250 IU IM should be given to all Rh(D)-negative women who miscarry after 12 weeks gestation (or any gestation after invasive procedure) within 72 hours. Psychological support and bereavement counselling are important components of care — many women experience significant grief, guilt, and anxiety after miscarriage.

Incomplete miscarriage with retained products of conception can cause infection (septic miscarriage) requiring urgent surgical evacuation and antibiotics. Heavy bleeding may require blood transfusion. Recurrent miscarriage (3+ consecutive losses) affects 1-2% of couples and warrants investigation for underlying causes including antiphospholipid syndrome and uterine abnormalities. Incomplete miscarriage with retained products of conception (RPOC) is the most common immediate complication — causing continued heavy bleeding and predisposing to endometritis. Septic miscarriage from ascending infection of retained products causes high fever, purulent discharge, and septicaemia — a medical emergency requiring broad-spectrum IV antibiotics (piperacillin-tazobactam or co-amoxiclav) and urgent surgical evacuation; delayed treatment risks septic shock and maternal death. Heavy haemorrhage from incomplete miscarriage — particularly with manual or failed medical management — may require blood transfusion, uterine tamponade, or surgical intervention including uterine artery embolisation. Cervical incompetence — discovered after second trimester losses — requires cervical cerclage placement in subsequent pregnancies. Rh(D) sensitisation occurs if anti-D immunoglobulin is not administered to Rh(D)-negative women, risking haemolytic disease of the newborn in subsequent pregnancies.

Many miscarriages cannot be prevented as chromosomal abnormalities are random. Optimize preconception health: manage diabetes and thyroid disease, take folic acid 400mcg daily, avoid smoking and alcohol, and achieve healthy BMI. Low-dose aspirin and heparin in antiphospholipid syndrome reduces recurrence. Progesterone supplementation in women with previous miscarriage and current bleeding may reduce risk (PRISM trial evidence). While chromosomal miscarriage is largely unpreventable, modifiable risk factors can be optimised before conception. Folic acid supplementation 400 mcg daily (5 mg daily in women with previous neural tube defect, diabetes, or anti-epileptic medication) from at least 1 month pre-conception through 12 weeks reduces neural tube defects and may marginally reduce miscarriage risk. Maintain healthy BMI (18.5-24.9) — both underweight and obesity increase miscarriage risk. Avoid smoking (miscarriage risk is dose-dependently increased by cigarette smoking), alcohol (any alcohol increases miscarriage risk — no safe level established), and illicit drugs. Optimise pre-existing conditions: tight glycaemic control in diabetes (HbA1c below 6.5% pre-conception reduces fetal loss significantly), thyroid function normalisation (TSH below 2.5 mIU/L), and treatment of antiphospholipid syndrome with low-dose aspirin 75 mg daily plus LMWH (enoxaparin 40 mg subcutaneously daily) reduces miscarriage risk by 50-60% in confirmed APS.

Go to A&E immediately for: very heavy vaginal bleeding (soaking through more than one pad per hour for 2 consecutive hours), severe pelvic pain not relieved by paracetamol, one-sided shoulder-tip pain (referred pain from diaphragmatic irritation — a warning sign of ectopic pregnancy rupture), fainting, dizziness, rapid heartbeat, or pale clammy skin (possible haemodynamic shock from ruptured ectopic pregnancy — a surgical emergency). Call your Early Pregnancy Unit (EPU) or GP for: any vaginal bleeding or cramping in pregnancy before 20 weeks — even light spotting warrants assessment; persistent severe nausea and vomiting preventing fluid intake; or if you are known to have a high-risk pregnancy. After a confirmed miscarriage, contact your GP or EPU if you develop fever, chills, or offensive-smelling vaginal discharge (signs of incomplete miscarriage with infection). Two or more consecutive miscarriages — request referral to a specialist recurrent miscarriage clinic for investigation and support. Emotional support is essential after miscarriage — ask your GP for referral to counselling or contact the Miscarriage Association.