What are the risk factors for silent miscarriage?

Risk Factors for Silent Miscarriage

Silent miscarriage (also known as missed miscarriage) occurs when a fetus dies but remains in the uterus without symptoms. 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

Maternal Age and Reproductive History Factors

• Advanced maternal age is a significant risk factor for silent miscarriage, with risk increasing progressively after age 35 2
• Advanced paternal age also contributes to increased miscarriage risk 2
• Previous miscarriage significantly increases the risk of subsequent miscarriage 2
• History of infertility and previous assisted conception are associated with higher miscarriage rates 2
• Previous pregnancy termination is linked to increased risk of subsequent miscarriage 2
• Changing partners between pregnancies may increase miscarriage risk 2

Biological and Physiological Factors

• Diminished ovarian reserve, as measured by low AMH levels (<1.0 ng/ml), increases miscarriage risk by approximately 35% (OR 1.35; 95% CI, 1.10-1.66) 3, 1
• Low pre-pregnancy body mass index (being underweight) is associated with higher miscarriage risk 4, 2
• Being overweight or obese also increases miscarriage risk 4
• Low serum levels of progesterone or human chorionic gonadotrophin (hCG) are risk factors for miscarriage 5
• Absence of pregnancy symptoms, particularly nausea, is associated with increased miscarriage risk 2

Lifestyle and Environmental Factors

• Regular or high alcohol consumption significantly increases miscarriage risk 4, 2
• Smoking is associated with increased risk of pregnancy loss 4
• High levels of psychological stress and experiencing traumatic events during pregnancy increase miscarriage risk 6, 2
• Poor emotional wellbeing contributes to increased risk of miscarriage 6
• Lack of vitamin supplementation and inadequate consumption of fresh fruits and vegetables are associated with higher miscarriage risk 2

Ultrasound and Clinical Findings

• Early gestational age at presentation with symptoms increases risk of subsequent miscarriage 5
• Heavy vaginal bleeding is associated with higher risk of pregnancy loss 5
• Empty gestational sac of >15-17 mm diameter on ultrasound indicates poor prognosis 5

Medical Conditions

• Pre-existing medical conditions, particularly cardiovascular disease, can increase risk of pregnancy complications including miscarriage 3
• Chronic health conditions that are part of the obstetrical comorbidity index (OB-CMI) including hypertension contribute to increased risk of adverse pregnancy outcomes 3

Preventive Factors

• Previous live birth is associated with reduced risk of miscarriage 2
• Nausea during early pregnancy is linked to lower miscarriage risk 6, 2
• Daily consumption of fresh fruits and vegetables appears protective 2
• Vitamin supplementation during early pregnancy reduces miscarriage risk 2

Understanding these risk factors can help identify women at higher risk for silent miscarriage and potentially guide preventive strategies, though many cases remain unexplained despite known risk factors. Women with multiple risk factors may benefit from closer monitoring during early pregnancy.