Women who menstruate more often than every 21 days or less often than every 35 days need to be evaluated for a cause. Women are supposed to have two hormones, estrogen and progesterone. Estrogen stimulates the uterus to grow. Progesterone stops the stimulation. If a woman has estrogen without progesterone, her uterus is stimulated all the time which can lead to uncontrolled growth, which is cancer. If a woman lacks both estrogen and progesterone, she is at risk for breaking her bones. Structural abnormalities of the uterus and vagina can interfere with menstruation, but most of the time, irregular periods are caused by abnormal ovarian function.
There are four types of irregular periods. A woman could be pregnant or in the menopause. A blood test called chorionic gonadotropin can diagnose pregnancy and FSH can diagnose menopause. She could have a brain tumor called a prolactinoma, which can be cured by taking bromocriptine pills. She could not be eating enough food, which is common in athletes and curable by eating more food. She also could have a defect in the way that her brain produces hormones (GnRH) that start her menstrual cycle and she will have estrogen, but no progesterone. These women usually have eggs that ripen but do not pop into the uterus. Women who have these conditions start to menstruate when they are given the second female hormone, progesterone. The most common cause is polycystic ovary syndrome (PCO or PCOS), which also can cause acne and obesity and can be treated effectively with a diabetic diet and drugs to lower blood insulin levels. All women with irregular periods need to be checked by a gynecologist and most need to be treated.