Risk Factors for Silent Miscarriage
Women with diminished ovarian reserve, characterized by low anti-Müllerian hormone (AMH) levels, have approximately 35% increased relative risk of silent miscarriage compared to those with normal ovarian reserve. 1, 2
Biological and Physiological Factors
- Advanced maternal age significantly increases risk for pregnancy-related complications including silent miscarriage; nearly one-third of all pregnancy-related deaths occur in women aged 35 years or older 3
- Advanced paternal age is independently associated with increased risk of first trimester miscarriage 4
- Low pre-pregnancy body mass index is associated with higher risk of first trimester miscarriage 4
- Being either underweight or overweight increases the risk of miscarriage 5
Medical Conditions and History
- Pre-existing chronic conditions, particularly cardiovascular disease, increase the risk of pregnancy complications including miscarriage 1
- Hypertension and other conditions included in the obstetrical comorbidity index (OB-CMI) contribute to increased risk of adverse pregnancy outcomes including silent miscarriage 1
- History of previous miscarriage significantly increases risk of subsequent miscarriage 5, 4
- History of infertility and previous use of assisted reproductive technologies increases miscarriage risk 6, 4
- Low serum levels of progesterone or human chorionic gonadotrophin (hCG) are risk factors for miscarriage 7
Lifestyle and Environmental Factors
- Smoking and high alcohol consumption are associated with increased risk of miscarriage 5, 4
- Regular or high alcohol consumption shows a stronger association with miscarriage risk than moderate or occasional consumption 4
- Psychological stress, including exposure to stressful or traumatic events, shows a dose-response relationship with miscarriage risk 4
- Changing partners between pregnancies is associated with increased miscarriage risk 4
Protective Factors
- Previous live birth is associated with reduced risk of miscarriage 4
- Nausea during early pregnancy is associated with lower risk of miscarriage 8, 4
- Vitamin supplementation before and during early pregnancy reduces miscarriage risk 4
- Daily consumption of fresh fruits and vegetables is associated with reduced risk of miscarriage 4
Ultrasound and Clinical Findings
- Early pregnancy ultrasound findings such as calcified yolk sac and expanded amnion sign indicate poor prognosis 2
- Heavy bleeding in early pregnancy, particularly when soaking more than one sanitary pad per hour, indicates higher risk of pregnancy loss 5
- Empty gestational sac of >15-17 mm diameter is associated with increased risk of miscarriage 7
Special Considerations
- Women with diminished ovarian reserve may have approximately 7% absolute increase in miscarriage risk (e.g., from 20% to 27%) 2
- Women attending early pregnancy assessment units with threatened miscarriage (vaginal bleeding with or without abdominal cramps) represent a particularly vulnerable group with higher risk of progression to complete miscarriage 8
- Women undergoing assisted reproduction are at greater risk of miscarriage compared to those conceiving naturally, particularly at advanced maternal age 6