Interpretation of elevated FSH in the regular menstrual cycle

In reproductive medicine, abnormal elevation of serum follicle stimulating hormone (FSH) concentrations during the luteofollicular transition is associated with low response in infertility treatment. Increasing levels of serum FSH in the early follicular phase is a characteristic of reproductive ageing and has become very popular for the determination of diminished ovarian oocyte reserve. In the case of elevated FSH in premenopausal women, many more (patho)physiological mechanisms other than ageing may be responsible and should be considered also. FSH concentrations may vary considerably due to a number of factors. Next to intra-, inter- and between different assays variation there is hourly-, cycle day dependent-, intercycle and life time variation. Furthermore, physiological conditions such as during puberty, in hereditary dizygotic twinning, after use of oral contraceptives and during lactation also elevated FSH levels can be found. Pathological conditions associated with significant increases in FSH are after unilateral ovariectomy, during recovery from hypothalamic amenorrhea and with excessive smoking. It should be kept in mind, that with the interpretation of an abnormal high FSH value, just as with any other abnormal laboratory result, one should be aware, that there may be a variety of underlying causes other than the one where was aimed at.