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

Miscarriage (spontaneous abortion) is the spontaneous loss of a pregnancy before the fetus reaches viability — defined as 24 weeks' gestation in the UK and most high-income countries, below 20-22 weeks in many other countries. Miscarriage is the most common complication of pregnancy, affecting 10-20% of clinically recognised pregnancies. When all conceptions are considered (including those lost before a missed period), the true prevalence is estimated at 30-50% — the majority of these early losses are unrecognised or mistaken for a late period. First trimester miscarriage (before 12 weeks) accounts for approximately 80% of all cases; second trimester miscarriage (12-24 weeks) accounts for approximately 20%. Miscarriage causes significant psychological distress — grief, anxiety, depression, and guilt are common responses — that is often underestimated by healthcare providers and society. Recurrent miscarriage (RM) — defined as 3 or more consecutive pregnancy losses — affects approximately 1-2% of couples and warrants systematic investigation for treatable underlying causes. Biochemical pregnancy loss (a positive pregnancy test followed by loss before an ultrasound-confirmable intrauterine pregnancy is seen) is not conventionally counted as a miscarriage in UK practice but causes significant distress and may be included in recurrent miscarriage investigations.

Chromosomal abnormalities in the embryo are the most common cause of sporadic miscarriage, accounting for 50-60% of first trimester losses. The most common chromosomal abnormalities causing miscarriage are: autosomal trisomies (particularly trisomy 16 — the most common; trisomies 13, 18, 21, and others); monosomy X (Turner syndrome — 45XO — the most common chromosomal cause in second trimester losses); triploidy (3n — usually from dispermy or diploid sperm/egg); and tetraploidy. These arise from errors in meiosis (usually in the oocyte — increases dramatically with advancing maternal age) and are random events not due to parental chromosome abnormalities. Maternal age is the single most important risk factor for sporadic miscarriage: risk is approximately 10-12% at age 20-30; 25% at age 35; 35% at age 40; and 50%+ at age 45. Other causes of sporadic miscarriage: uterine structural abnormalities (submucous fibroids distorting the cavity; uterine septum — most common uterine anomaly causing recurrent miscarriage; bicornuate uterus; Asherman's syndrome — intrauterine adhesions); thyroid disease (hypothyroidism and hyperthyroidism both increase miscarriage risk — routine TSH screening before/early pregnancy recommended); poorly controlled type 1 or 2 diabetes (HbA1c above 86 mmol/mol in the first trimester — 3-fold increased miscarriage risk); thrombophilia (antiphospholipid syndrome/APS — the most important treatable cause of recurrent miscarriage; also inherited thrombophilias — Factor V Leiden, prothrombin gene mutation). Causes of recurrent miscarriage (RM): APS (antiphospholipid syndrome) — found in 15-20% of RM couples — requires treatment with low-dose aspirin and low-molecular-weight heparin (LMWH) throughout pregnancy; parental chromosomal abnormality (particularly balanced reciprocal or Robertsonian translocation — found in 3-5% of RM couples — warrants referral to clinical genetics); uterine anomaly (particularly uterine septum — surgical correction may improve outcomes); immunological factors; thrombophilias; and unexplained (accounts for 50-75% of RM after investigation). Lifestyle risk factors: smoking (increases risk by 50%); alcohol (more than 2 units/day — dose-dependent increase); caffeine above 200 mg/day; illicit drug use; BMI above 30 (obesity) and below 18.5 (underweight); and vaginal bleeding in early pregnancy.

Miscarriage presents across a clinical spectrum — from complete asymptomatic loss detected on routine scan to life-threatening haemorrhage. Types of miscarriage: Threatened miscarriage: vaginal bleeding (often light spotting or heavier) with or without pelvic cramping, but the cervical os is closed on examination; the fetus is still alive on ultrasound — up to 50% of threatened miscarriages proceed to viable pregnancy. Inevitable miscarriage: cervical os is open (dilated) on examination — miscarriage is imminent and cannot be prevented. Incomplete miscarriage: some products of conception remain in the uterus after partial expulsion — typically presents with heavy bleeding, cramping, and an open cervical os. Complete miscarriage: all products of conception have been expelled — the uterus is empty on ultrasound and bleeding settles. Missed (silent) miscarriage: the fetus has died but has not been expelled — typically discovered incidentally on ultrasound (no fetal heart seen, fetal pole present, or gestational sac empty — 'blighted ovum' or anembryonic pregnancy); often asymptomatic or minimal symptoms. Recurrent miscarriage: 3 or more consecutive losses. Symptoms of miscarriage: vaginal bleeding (ranging from light spotting to heavy with clots — heavier bleeding usually accompanies incomplete or inevitable miscarriage); lower abdominal cramping (uterine contractions); passage of tissue or clots per vagina; and loss of pregnancy symptoms (nausea, breast tenderness — these symptoms subside when the pregnancy fails). Septic miscarriage: miscarriage complicated by infection — fever, uterine tenderness, offensive discharge, systemically unwell — requires urgent antibiotics and evacuation of infected tissue.

Transvaginal ultrasound (TVS) is the gold standard for diagnosing miscarriage — more sensitive than transabdominal ultrasound in early pregnancy. Ultrasound findings: fetal heartbeat absent in an embryo with a crown-rump length (CRL) above 7mm (NICE recommends 7mm threshold — confirms miscarriage if no FH at CRL 7mm or above); empty gestational sac (mean sac diameter above 25mm without a visible embryo — anembryonic pregnancy); retained products of conception (incomplete miscarriage). Second scan at interval of 7-14 days: UK guidelines recommend a repeat scan if diagnosis is uncertain (CRL below 7mm without FH, MSD below 25mm) to definitively confirm miscarriage and avoid intervention in a viable pregnancy. Serum beta-hCG (human chorionic gonadotropin): normal intrauterine pregnancy: beta-hCG doubles every 48-72 hours in the first trimester; a rise of less than 50% in 48 hours or falling beta-hCG supports miscarriage or ectopic pregnancy; serial hCG is essential when ultrasound is inconclusive (gestational sac too small to visualise intrauterine pregnancy). Progesterone: a progesterone above 25 nmol/L is strongly reassuring of an ongoing pregnancy; below 16 nmol/L suggests a failing pregnancy. Blood tests: full blood count (assess degree of blood loss and anaemia); blood group and Rh factor (all Rh-negative women with miscarriage require anti-D immunoglobulin to prevent Rh sensitisation); coagulation screen (if heavy blood loss). Recurrent miscarriage investigation panel (after 3 losses or 2 with additional risk factors): antiphospholipid antibody screen (lupus anticoagulant, anticardiolipin IgG/IgM, anti-beta2-glycoprotein I — positive on 2 occasions at least 12 weeks apart); parental karyotype; pelvic ultrasound (uterine anomaly); thrombophilia screen (in selected cases — NICE 2023 recommends only if strong clinical suspicion); thyroid function and thyroid antibodies.

Management of miscarriage is offered across three approaches — expectant, medical, or surgical — with equal overall safety and efficacy. The woman's preference is central to management decisions. Expectant management: allowing the miscarriage to complete naturally — complete resolution occurs in 80% of incomplete miscarriages within 2 weeks, but in only 50% of missed miscarriages at 2 weeks and 80% by 4 weeks. Not suitable for heavy bleeding, infection, or when the woman requests definitive management. Medical management with misoprostol (a prostaglandin E1 analogue — 800 mcg vaginally or sublingually) — the most commonly used medical management: causes uterine contractions and expulsion of products within 24-48 hours; complete in approximately 80% at 2 weeks; may need repeat dose or surgical completion. Anti-emetics and strong analgesia (ibuprofen, co-codamol, opioids if needed) are prescribed alongside. Surgical management (ERPC — evacuation of retained products of conception, formerly called 'D&C'): either under general anaesthesia (surgical suction curettage — most complete and definitive) or manual vacuum aspiration (MVA) under local anaesthesia in an outpatient setting — success rate above 95%. Indicated for: haemodynamic instability from heavy bleeding; failed medical management; septic miscarriage (urgent); or patient preference. Rh immunisation prophylaxis: Anti-D immunoglobulin 250 iu IM to all Rh-negative women who have surgical or medical management of miscarriage at any gestation, or expectant management of miscarriage at or above 12 weeks. Recurrent miscarriage treatment: APS — low-dose aspirin 75mg daily + LMWH (enoxaparin 40mg daily) from positive pregnancy test — reduces miscarriage risk from 90% to approximately 25-30% in APS; uterine septum — surgical correction (hysteroscopic metroplasty) — reduces miscarriage risk in subsequent pregnancies; progesterone supplementation — PROMISE trial: vaginal progesterone 400mg twice daily from positive pregnancy test may benefit women with recurrent miscarriage and unexplained bleeding (modest but significant benefit); thyroid disease — optimise before conception (TSH below 2.5 mIU/L in first trimester). Psychological support: the emotional impact of miscarriage is significant and often underestimated — all women should be offered information about support services (Miscarriage Association UK, Tommy's National Centre); formal counselling or peer support for recurrent miscarriage.

Miscarriage causes both immediate medical and significant long-term psychological complications. Medical complications: haemorrhage (heavy vaginal bleeding) requiring blood transfusion occurs in approximately 1–2% of cases managed expectantly or medically, and may require emergency surgical evacuation; septic miscarriage (ascending uterine infection — Escherichia coli, Streptococcus, Staphylococcus) causes endometritis, pelvic inflammatory disease, and can progress to septic shock and multi-organ failure — a medical emergency requiring immediate IV broad-spectrum antibiotics and urgent surgical evacuation. Retained products of conception (RPOC) can complicate any management modality, causing persistent bleeding and infection; diagnosis is by ultrasound and treatment is surgical. Rh sensitisation: Rh-negative women who are not given anti-D immunoglobulin after miscarriage may develop antibodies causing haemolytic disease of the newborn in future Rh-positive pregnancies — anti-D is mandatory after surgical or medical management. Asherman's syndrome (intrauterine adhesions) — a rare but serious complication of repeated surgical evacuation — causes menstrual abnormalities, subfertility, and recurrent miscarriage; managed by hysteroscopic adhesiolysis. Gestational trophoblastic disease: a rare complication where abnormal trophoblastic cells proliferate after a hydatidiform molar pregnancy — requires surveillance with serial beta-hCG and in some cases chemotherapy. Psychological complications: grief, depression, anxiety, and PTSD are highly prevalent — approximately 30% of women experience significant psychological morbidity persisting for 6–12 months; recurrent miscarriage causes compounding distress and should prompt formal psychological support referral.

For most women, the first or second miscarriage is due to a random chromosomal error in the embryo and cannot be prevented — the majority of these women will have a successful subsequent pregnancy. Modifiable lifestyle factors that reduce miscarriage risk: achieving healthy weight before conception (BMI 18.5-25); smoking cessation (reduces miscarriage risk by approximately 50%); limiting alcohol to zero (abstinence is safest in pregnancy); reducing caffeine below 200 mg/day (2 cups of coffee); treatment of pre-existing medical conditions (diabetes control — aim HbA1c below 48 mmol/mol before conception; thyroid disease — normalise TSH; epilepsy medication review); and folic acid supplementation 400-5,000 mcg daily for at least 3 months before conception and throughout the first trimester. For recurrent miscarriage: investigate and treat treatable causes (APS — aspirin and LMWH; uterine septum — hysteroscopic resection; thyroid disease — optimise TSH). Progesterone supplementation (400mg vaginal twice daily from positive test until 16 weeks) should be discussed for women with a history of recurrent miscarriage and unexplained early pregnancy bleeding (PROMISE and PRISM trial evidence). Low-dose aspirin (75mg daily from pre-conception) for APS-associated recurrent miscarriage. Early pregnancy support clinics (EPU review from 6-8 weeks gestation — early scan for reassurance) may reduce anxiety in future pregnancies.

Go to an emergency department or early pregnancy unit immediately for: heavy vaginal bleeding (soaking more than one pad per hour for 2+ hours) — may indicate significant haemorrhage requiring urgent intervention; severe one-sided pelvic pain with bleeding in early pregnancy — this is the presentation of ectopic pregnancy (a potentially life-threatening condition) until proven otherwise; signs of infection (fever above 38°C, offensive vaginal discharge, severe uterine tenderness, rigors); feeling faint, dizzy, or collapsing with early pregnancy bleeding (haemodynamic compromise); and shoulder tip pain with bleeding (diaphragmatic irritation from intraperitoneal blood — ectopic pregnancy). Go to an early pregnancy unit (EPU) promptly within 24-48 hours for: any vaginal bleeding in early pregnancy for assessment (ultrasound + beta-hCG + Rh status); no fetal movement detected after a previously normal scan; or pregnancy symptoms that have suddenly stopped. After a confirmed miscarriage: seek GP or gynaecology review if bleeding has not settled within 2 weeks of treatment; if you develop fever or offensive discharge (infection — septic miscarriage); or if a pregnancy test remains positive 3 weeks after miscarriage (retained products or, rarely, gestational trophoblastic disease).