If you have gone to your doctor for a preconception checkup or even have sought fertility treatments one of the first tests which may be done to assess your fertility level is to check your level of follicle stimulating hormone (FSH). This hormone is a method of seeing how responsive your ovaries are to the chemical signals which result in egg production. The higher your FSH level is the less responsive your ovaries are and the less likely a pregnancy will occur. Doctors often use FSH as a way of determining if you are close to menopause, or close to menopause.
A woman's fertility is often ‘graded’ according to her FSH level with levels under 7 being considered fertile, levels around 21 considered pre-menopausal and levels over 45 postmenopausal. Although “age and reproductive stage are the most important determinants of FSH levels in US women using a woman's levels of follicle-stimulating hormone (FSH) appears to be a poor guide to her menopausal status, research suggests. (Janet Henrich et al. , Yale University School of Medicine, New Haven, Connecticut, USA)
They looked at the fertility of women between 35 and 60 years of age. They did find that FSH level increased significantly with age and that reproductive stage was associated with FSH levels however they also found that the three stages, fertility, pre-menopause and menopause showed a wide overlap in FSH levels. For example, doctors often use an FSH level of 13 as a cutoff point where women who have FSH levels greater than 13 are considered pre-menopausal and women with FSH under 13 are still considered fertile. What the researchers found however, was that some women (23%) who were fertile had FSH levels higher than 13 while some women who were pre-menopausal could have levels which were less than 13. So, using a value of 13 as a cut off was not always accurate.
Similarly, they found that using the cutoff of 45 to distinguish between menopausal and postmenopausal stages was correct 73% of the time but 27% of women would be incorrectly diagnosed as postmenopausal with this cut off point.
It is important to note that although FSH is a useful tool to get an indication of fertility it is not an absolute and is subject to fluctuations from cycle to cycle and also has some margin of error in it's ability to predict your fertility.
Reference: Menopause 2006; 13: 171-7
Pat Antliff B. A. M. Ed
Pat is a professional fertility coach and owner of http://www.fertilityover40.com