The classic definition of recurrent miscarriage is having three or more consecutive spontaneous abortions. However, in recent years, it has been recognized that one need not wait until the third miscarriage to start investigating the causes; investigation can begin after a second miscarriage. This approach has been widely accepted by obstetricians and gynecologists both domestically and internationally.
The incidence of early spontaneous abortion is relatively high, reported at 10% to 18%. With the clinical use of highly sensitive β-hCG tests, many cases have been identified where the result was positive before menstruation but then resulted in a miscarriage, known as a "subclinical" or "hidden" miscarriage. In these cases, the patient may experience a slightly delayed period with slightly heavier or normal menstrual flow, which is actually an unimplanted embryo miscarriage. If such cases are also counted as spontaneous abortions, the incidence of natural abortion could be as high as 50% to 60%. When a fertilized egg does not meet all the conditions for full development, the body's natural protective mechanism expels it early to terminate the pregnancy. However, if repeated early miscarriages occur, it is important to investigate the underlying causes. If the cause is correctable and treated appropriately, it is possible to have a healthy baby.