Early Pregnancy Loss: Etiology

The etiology of early pregnancy loss is varied and often controversial. More than 1 etiologic factor is often present. The most common causes of recurrent miscarriages are as follows:

• Genetic causes
  • Mendelian disorders
  • Genetic translocations
  • Multifactorial disorders
  • Chromosomal inversions
  • Sex-chromosome aneuploidies
• Autoimmune causes
  • Immunologic causes
  • Alloimmune causes
• Anatomic causes
  • Uterine müllerian anomaly
    • Uterine septum (the anomaly most common associated with pregnancy loss)
    • Hemiuterus (unicornuate uterus)
    • Bicornuate uterus
  • Diethylstilbestrol-linked condition
  • Acquired defects (eg, Asherman syndrome)
  • Incompetent cervix
  • Leiomyomas
  • Uterine polyps
• Infectious causes
• Environmental causes
  • Smoking
  • Excessive alcohol consumption
• Endocrine factors
  • Diabetes mellitus
  • Antithyroid antibodies
  • Luteal-phase deficiency
• Hematologic disorders

The gestational age at the time of the SAB can provide clues about the cause. For instance, nearly 70% of SABs in the first 12 weeks are due to chromosomal anomalies. However, losses due to antiphospholipid syndrome (APS) and cervical incompetence tend to occur after the first trimester.