12. The normal and abnormal menstrual cycle

The regulation of the menstrual cycle in women is an intricate interplay between the hypothalamic, pituitary and gonadal hormones. Immediately following menarche most menstrual cycles are anovulatory and hence the interval between menstruations is slightly irregular. After 2–4 years most girls will have regular periods. However, a small number will continue to have irregular or even absent menses. Other women will develop irregular cycles later on in life as they gain weight. In others the disappearance of menses might be associated with other disturbing symptoms. Anovulatory cycles are classified as having central, peripheral or combined causes. Apart from subfertility, anovulation is also associated with other short-term as well as long-term health issues such as hirsutism, obesity, metabolic syndrome, cardiovascular disease, osteoporosis and type 2 diabetes mellitus. Therefore, women with irregular menstrual cycles deserve proper medical attention, appropriate care and sufficient follow-up during their whole lifespan in order to prevent and timely treat some of the disturbing symptoms and health sequelae later on in life.