Causes of Miscarriages
The main causes of miscarriages include chromosomal abnormalities (accounting for approximately 70% of sporadic miscarriages), diminished ovarian reserve, blood coagulation disorders, uterine abnormalities, endocrine disorders, immunological factors, and environmental factors. 1, 2
Chromosomal Abnormalities
- Chromosomal defects are the leading cause of first-time miscarriages
- Can be either numerical (aneuploidy) or structural defects in either parents or fetus
- Risk increases with maternal age (particularly over 35 years) and paternal age (over 40 years) 3
Diminished Ovarian Reserve
- Associated with approximately 35% higher relative risk of miscarriage compared to normal ovarian reserve 4
- Impacts both quantity and quality of eggs, leading to increased embryo aneuploidy
- Measurable through:
- Low serum Anti-Müllerian Hormone (AMH) levels
- Low Antral Follicle Count (AFC) on ultrasound
- Risk is particularly significant in women over 35 years 5
- Women with low AMH (<0.7 ng/ml) have approximately 91% higher odds of miscarriage 5
Blood Coagulation Disorders
- Account for approximately 55% of recurrent miscarriages 6
- Major coagulation disorders associated with miscarriage:
- Antiphospholipid syndrome (67% of coagulation-related miscarriages)
- Sticky platelet syndrome (21%)
- Tissue plasminogen activator deficiency (9%)
- Factor V Leiden mutation (7%)
- Protein S deficiency (5%)
- Other thrombophilias 6
- These disorders cause thrombosis and infarction of placental vessels
Uterine Abnormalities
- Anatomical defects of the uterus contribute to approximately 10-15% of recurrent miscarriages 6
- Include congenital malformations, fibroids, and adhesions
Endocrine Disorders
- Account for approximately 15% of recurrent miscarriages 6
- Include:
- Thyroid dysfunction
- Polycystic ovary syndrome
- Luteal phase defects
- Diabetes mellitus
Immunological Factors
- Abnormal maternal immune response to the fetus
- Includes:
- Natural killer cell dysfunction
- Regulatory T cell abnormalities
- Abnormal cytokine production
- Tumour necrosis factor α imbalance 7
Environmental and Lifestyle Factors
- Smoking
- Alcohol consumption
- High stress levels
- Night shift work
- Air pollution
- Pesticide exposure
- Very low or very high body mass index 3
Epidemiology and Impact
- Approximately 23 million miscarriages occur worldwide annually (44 pregnancy losses per minute)
- Overall risk is 15.3% of all recognized pregnancies
- Population prevalence: 10.8% of women have had one miscarriage, 1.9% have had two, and 0.7% have had three or more 3
- Psychological consequences include increased risk of anxiety, depression, post-traumatic stress disorder, and suicide
- Miscarriage is a sentinel risk marker for future obstetric complications and long-term health problems 3
Risk Reduction
- For women with blood coagulation disorders, treatment with preconception aspirin (81 mg/day) and postconception heparin (5000 U every 12 hours) has shown >98% success rate in achieving normal term delivery 6
- Management of endocrine disorders, particularly thyroid dysfunction
- Avoidance of modifiable risk factors (smoking, alcohol, extreme BMI)
Understanding the specific cause of miscarriage is crucial for appropriate management and counseling regarding future pregnancies, though approximately 50% of recurrent miscarriages remain unexplained despite thorough evaluation 2, 7.