Breakthrough bleeding, or bleeding in between periods, usually only lasts for one to three days, according to Everyday Health. Heavy bleeding or long periods of breakthrough bleeding should be investigated by a doctor.
Breakthrough bleeding, also known as spotting, is extremely common and is something that almost all women experience at some point. It is often the first sign of pregnancy, and it can occur during perimenopause, explains Everyday Health. Usually, the cause is an upset to a woman's normal cycle, such as stress or a change in birth control medications. Rarely, spotting can be a sign of a more serious problem, such as miscarriage, ectopic pregnancy, endometriosis or cancer of the cervix, uterus or endometrium.