Recurrent miscarriage is defined as the loss of 3 or more consecutive pregnancies and is a stressful condition for both patients and clinicians alike. It affects about 1% of all fertile couples trying to conceive, in comparison with sporadic non-consecutive miscarriages, which occur in about 15% to 20% of all pregnancies.  It includes all pregnancies that end before the age of viability, which currently stands at 24 weeks' gestation. Miscarriages that occur before 12 weeks' gestation are commonly termed early or first-trimester miscarriages, and those that occur between 13 and 24 weeks' gestation are known as late or second-trimester miscarriages.
Evaluation can start after 2 or 3 consecutive miscarriages, as prevalence of causes is similar in those with 2, 3, or more miscarriages.  Despite a wide range of investigations, no apparent cause is found in more than 50% of cases of recurrent miscarriage.  In spite of this, 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.   Created by the BMJ Group; data from Brigham SA, et al. Hum Reprod. 1999;14:2868-2871
Definite associations of recurrent miscarriage include chromosomal abnormalities, antiphospholipid syndrome, certain structural uterine abnormalities such as cervical incompetence, 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 also surrounds the possible association of other conditions with recurrent miscarriage, including immunological factors, other uterine abnormalities (e.g., bicornuate or septate uterus), and endocrinological factors. There is a need for high-quality and methodologically sound research to guide management of these patients.
Increasing maternal age reduces the chance of a successful live birth. Women aged 20 years with 2 previous miscarriages have a 92% chance of success in the next pregnancy compared with only a 60% chance of success in women aged 45 years. 
Paternal age also plays a part. Frequency of chromosomal anomalies in sperm appears to increase with age. Independent of maternal age, paternal age of more than 40 years carries 1:6 odds of miscarriage compared with paternal age of 25 to 29 years.  Older couples have the worst pregnancy rates and outcome. 
Primigravidas and patients who consistently have successful pregnancies have only about 5% risk of miscarriage, compared with 24% in patients who have previously miscarried.  Other studies similarly show a trend of miscarriage rate increasing with the number of previous miscarriages.   Therefore, the risk of miscarriage is directly related to the outcome of previous pregnancies.
Recurrent miscarriage is a stressful condition, so alongside medical investigations and appropriate treatment, patient education, counselling, and support should be provided.