Researchers at the University of Michigan say soon it will be possible to predict when women are likely to begin menopause.
The scientists say they have found new information about hormonal biomarkers that can indicate the beginning of the menopause to within a year.
This is significant because for many women, including the growing number who choose to start families later in life, predicting their biological clock's relation to the timing of their menopause and infertility is critically important.
Professor MaryFran Sowers from from the Department of Epidemiology says the information provides a roadmap as to how fast women are progressing through the different elements of their reproductive life and could change the way women behave.
A research team led by Sowers 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 discovered that the biomarker AMH declined to a very low or non-measurable level five years prior to the final menstrual period, a decline which signals a critical stage in which a woman probably has so few follicles (eggs) that her fertility becomes increasingly questionable.
Professor Sowers says the changes in AMH and inhibin B concentrations were found to be predictive of the time to menopause.
The research team also measured and reported the rates of change 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, the 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.