Study leader MaryFran Sowers of the University of Michigan School of Public Health and colleagues examined the naturally occurring changes in three biomarkers over the reproductive life of more than 600 women: follicle-stimulating hormone, or FSH; anti-Mullerian hormone, or AMH; and inhibin B.

"In the end, this information can change the way we do business," Sowers said in a statement. "The information provides a road map as to how fast women are progressing through the different elements of their reproductive life."

The researchers 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 fertility becomes increasingly questionable, Sowers said.

The team found that the changes in AMH and inhibin B concentrations were predictive of the time to menopause.

The findings is available online at the Journal of Clinical Endocrinology and Metabolism.