Recurrent miscarriage is defined by the European Society for Human Reproduction and Embryology and the American Society for Reproductive Medicine as 2 or more failed clinical pregnancies (i.e., documented by ultrasound or histopathology).[1][2] It affects about 1% of all fertile couples trying to conceive, in comparison with sporadic nonconsecutive miscarriages, which occur in about 15% to 20% of all pregnancies.[3] A miscarriage includes any pregnancy that ends before the age of viability, which currently stands at 24 weeks' gestation. A miscarriage that occurs before 12 weeks' gestation is commonly termed an early or first-trimester miscarriage, and one that occurs between 13 and 24 weeks' gestation is known as a late or second-trimester miscarriage.
Evaluation can start after 2 or 3 consecutive miscarriages, as prevalence of causes is similar in those with 2, 3, or more miscarriages.[4] Despite a wide range of investigations, no apparent cause is found in >50% of cases of recurrent miscarriage.[5] About 70% of patients with no cause found will achieve a live birth in the subsequent pregnancy depending on the age of the woman and the number of previous miscarriages.[4] [5]
Definite associations of recurrent miscarriage include chromosomal abnormalities, antiphospholipid syndrome, certain structural uterine abnormalities such as septate uterus, and certain thrombophilias. However, a reduction in risk of miscarriage in a subsequent pregnancy following treatment has not been proven unequivocally for most of these conditions. Controversy surrounds the possible association of other conditions with recurrent miscarriage, including immunologic factors, other uterine abnormalities (e.g., cervical incompetence), infection, and male and endocrinologic factors. There is a need for high-quality and methodologically sound research to guide management of these patients.[6]
