To determine the frequency of factors associated with habitual abortion in 197 couples. Prospective cohort study. The British Columbia Recurrent Pregnancy Loss Program, located in a tertiary care academic center. Diagnostic screening protocol. Genetic, endocrine, infectious, anatomical, and autoimmune factors associated with habitual abortion. A structural genetic factor was identified in 3.5% of the couples. An endocrine factor, including luteal phase deficiency and hypothyroidism, was identified in 20% and an infectious factor was identified in 0.5% of the couples. An anatomical factor, including various müllerian tract anomalies and severe intrauterine adhesions, was found in 16% and an autoimmune factor, including the antiphospholipid antibody syndrome and the undifferentiated connective tissue syndrome, was identified in 20% of the couples. Eighty-four couples who completed the diagnostic screening protocol were classified as having unexplained habitual abortion. Of these 84 couples, 65% were subclassified as primary, 27% were subclassified as secondary, and 7% had unclassified unexplained habitual abortion. This large-scale study identified genetic, endocrine, infectious, anatomical, or autoimmune factors in approximately 60% of couples with habitual abortion.
