According to WebMD, the signs of a miscarriage include heavy or light vaginal bleeding that may be regular or irregular; pain in the pelvis, belly or lower back; and blood clots or clots of gray tissue. A miscarriage occurs over several days and includes any of the aforementioned symptoms.
WebMD explains that a woman's risk for miscarriage increases when she or her partner are over the age of 35. Alcohol, cigarette, cocaine and excessive caffeine use also increase the risk of miscarriage. Unpreventable medical conditions, such as polycystic ovary syndrome, blood-clotting disorders and bacterial or viral infections, may also cause a miscarriage.