There are many factors which can contribute to miscarriage including the mother's age (risk increases as mothers age), hormonal issues, improper egg implantation, truama to the mother, and lifestyle. However, some miscarriages take place for no discernable reason.
Most miscarriages take place within the first 13 weekes of pregnancy.
More About Miscarriage
The is no way to completely prevent a miscarriage. Doctors advise expectant mothers to exercise, eat a healthy diet, manage their weight, avoid stress, eliminate smoking and alcohol, and take folic acid.