Risk Factors for Miscarriage
Advanced maternal age is the most significant risk factor for miscarriage, with women over 35 years having substantially higher risk compared to younger women. 1
Demographic Risk Factors
- Age: Women younger than 20 years and older than 35 years have increased risk, with risk progressively increasing after age 35 1
- Male partner age: Men older than 40 years contribute to increased miscarriage risk 1
- Body Mass Index (BMI): Both very low (≤20 kg/m²) and very high BMI (≥30 kg/m²) are associated with increased risk 1, 2
- Ethnicity: Black ethnicity is associated with higher miscarriage rates 1
Lifestyle and Environmental Factors
- Smoking: Active smoking increases miscarriage risk 1
- Alcohol consumption: Any alcohol intake during pregnancy increases risk 1
- Stress: Higher perceived stress levels correlate with increased miscarriage risk, supported by elevated corticotrophin-releasing hormone concentrations 2
- Working night shifts: Disruption of circadian rhythm increases risk 1
- Environmental exposures: Air pollution and pesticide exposure are associated with higher miscarriage rates 1
Medical and Obstetric History
- Previous miscarriages: History of prior pregnancy loss significantly increases risk for subsequent miscarriages 1
- Recurrent miscarriage: Women with history of three or more miscarriages (affecting 0.7% of women) have significantly higher risk in subsequent pregnancies 1
- Diminished ovarian reserve: Low anti-Müllerian hormone (AMH) levels are associated with approximately 35% increased relative risk of miscarriage 3
Hematologic and Immunologic Factors
- Antiphospholipid syndrome: Accounts for approximately 67% of recurrent miscarriages with procoagulant defects 4
- Sticky platelet syndrome: Responsible for about 21% of recurrent miscarriages with procoagulant defects 4
- Thrombophilias: Factor V Leiden (7%), protein S deficiency (5%), antithrombin deficiency (2%), and protein C deficiency (1%) contribute to recurrent pregnancy loss 4
- Fibrinolytic disorders: Tissue plasminogen activator deficiency (9%) and elevated plasminogen activator inhibitor-1 (6%) increase risk 4
Endocrine Disorders
- Poorly controlled diabetes: Uncontrolled blood glucose increases miscarriage risk 5
- Polycystic ovary syndrome (PCOS): Associated with higher miscarriage rates 5
- Hypothyroidism: Untreated or poorly controlled hypothyroidism increases risk 5
- Low progesterone levels: Serum progesterone concentrations ≤12 ng/ml are associated with higher miscarriage risk 2
- Reduced progesterone-induced blocking factor: Lower concentrations correlate with increased risk 2
Anatomical Factors
- Uterine malformations: Congenital anomalies of the uterus contribute to recurrent pregnancy loss 5
- Intrauterine adhesions: Scarring within the uterine cavity increases risk 5
Genetic Factors
- Chromosomal abnormalities: Account for approximately 7% of recurrent miscarriages 4
- Genetic polymorphisms: Various genetic variations are associated with recurrent pregnancy loss 5
Clinical Implications
- Miscarriage is a sentinel marker for future obstetric complications including preterm birth, fetal growth restriction, placental abruption, and stillbirth 1
- Women with history of recurrent miscarriage have increased long-term health risks including cardiovascular disease and venous thromboembolism 1
- Early pregnancy ultrasound findings that indicate poor prognosis include calcified yolk sac and expanded amnion sign (enlarged amniotic cavity relative to crown-rump length) 6
Risk Assessment
- First-trimester miscarriage risk is particularly elevated in women with multiple risk factors 2
- The highest risk period is between 4-7 weeks gestation, when risk factors have their strongest impact 2
- Women with diminished ovarian reserve may have approximately 7% absolute increase in miscarriage risk (e.g., from 20% to 27%) 3
Understanding these risk factors allows for appropriate preconception counseling and early pregnancy monitoring for women at increased risk of pregnancy loss.