Uterine anomalies are a common cause and are classified as congenital (from birth) or acquired (develop over time). An example of a congenital anomaly is a uterine septum, which is an area within the uterus which is felt to provide poor blood supply to a developing fetus. An example of an acquired anomaly is a tumor such as a polyp or fibroid. These anomalies are discussed in further detail here
Medical conditions that alter blood flow can be a cause of pregnancy loss as well and can be fully investigated at an appropriate laboratory. These abnormalities are usually treated by medication that prevent the blood clots that ultimately impair the blood flow.
Genetic conditions can be a cause of many miscarriages and can be random in nature. This random type of genetic abnormality is usually caused by a process called meiotic nondisjunction and is more common among females as they age. A different genetic condition, called a balanced reciprocal translocation, is present from birth in one or both of the parents. Unfortunately, a pregnancy that results under these conditions may have an abnormal number of chromosomes as a result of this translocation. Genetic testing of the parents' blood called a karyotype is recommended.
Unfortunately, in many cases, the cause of miscarriage is unknown. Fortunately, empirical supportive treatments over time will commonly lead to a successful delivery. A thorough discussion of testing and treatment strategies can be reviewed with patients prior to treatment decisions being made.