Vaginal bleeding that does not result from a menstrual period can be considered abnormal, and there are several causes for this depending on a woman's current medical situation. According to WebMD, spotting can occur before a menstrual cycle, when pregnant and when periods cease at menopause.
If the woman knows for sure that she is not pregnant, then spotting between periods does not necessarily mean that something is medically wrong. According to WebMD, when a woman ovulates, it can cause bleeding between normal cycles, which is not a cause for alarm. If a woman is pregnant, spotting can be considered normal as long as the spotting does not turn into heavy bleeding. Any bleeding other than spotting can be signs of a miscarriage or an ectopic pregnancy, and a woman should seek medical care right away. A hormonal imbalance called polycystic ovary syndrome can interfere with normal menstrual cycles and cause abnormal bleeding. Birth control medicines can cause spotting, especially during the first few months of taking it or if the birth control medicine is not taken on a daily basis. An infection in the pelvic organs and many STDs can also cause abnormal bleeding. Aside from sexual activity, stress and exercise can also effect a woman's menstrual cycle and cause spotting. WebMD advises consulting with a doctor to find out the exact cause of spotting.