"The information provides a roadmap as to how fast women are progressing through the different elements of their reproductive life," said MaryFran Sowers, professor in the U-M School of Public Health Department of Epidemiology.
The researchers examined the naturally occurring changes in three different biomarkers over the reproductive life of more than 600 women: follicle-stimulating hormone (FSH), anti-Mullerian hormone (AMH) and inhibin B.
They found that the biomarker AMH declined to a very low or non-measurable level five years prior to the final menstrual period.
This decline pinpoints a critical juncture in which a woman probably has so few follicles (eggs) that her fertility becomes increasingly questionable, Sowers said.
They found that the changes in AMH and inhibin B concentrations were predictive of the time to menopause.
The research team also saw changes in FSH, and used the information to identify different reproductive stages
Based on a woman's age and the level of FSH in the blood, researchers were able to describe four different stages that occur for women from their late reproductive period to the time of their final menstrual period.
"People really want information about how long do I have and when will I have my final menstrual period," Sowers said.
"Now we are beginning to say, 'If you have a specific FSH level combined with your age, this is the likelihood that you are in this reproductive stage.'
"We finally have numbers from enough women evaluated over a long time period to describe the reproductive aging process. It begins to give women and clinicians an expanded way to look at menses and endocrine events in terms of reproductive progression," she added.