Pregnancy, miscarriage, ovulation, polycystic ovary syndrome, birth control or pelvic inflammatory disease can cause spotting before a period, explains WebMD. Most women experience abnormal bleeding, and it isn't always dangerous unless other symptoms are present.
Spotting before an expected period is a cause for concern if the bleeding is heavy or if it occurs during sex. WebMD explains that heavy bleeding accompanied by painful sexual intercourse may be a sign of a sexually transmitted infection.
WebMD says that some women experience light bleeding in the early weeks of pregnancy. The fertilized egg implanting into the uterine wall causes the bleeding.
Women on birth control, especially those who use an intrauterine device, are more likely to experience heavy spotting prior to their regular periods. WebMD states that hormonal birth control pills can cause intermittent bleeding due to the hormonal changes. Missing a birth control pill may cause a woman to bleed between periods as well.
While spotting isn't considered life threatening, there are serious complications that can cause spotting. For example, Web MD explains that heavy spotting may be caused by uterine fibroids, cancer, sexual abuse, structural problems, extreme stress, perimenopause or remnants of fetal material in the uterus after birth or an abortion.