No one knows for sure when a woman's biological clock will stop ticking, but eventually, it does.
It's an alarming thought for some women who've put off having children in favor of a career or other life pursuits.
Now a new study suggests it may soon be possible for women to predict when they'll go through menopause, then calculate when they'll likely run out of eggs, since that happens about 15 years before menopause hits.
In the current study, doctors in Iran took blood samples from 266 women then measured their levels of a hormone that can show how many eggs are left in the ovaries.
Researchers said the test was able to predict when menopause would set in within a four month window.
Whether the test will be as accurate in future studies remains to be seen.
Some fertility experts are skeptical about using it in clinical practice.
"Since only 2% of people have what we call premature menopause before 40, is it worth testing everyone to find out which 2% are gonna be in pre-menopause?" asks Dr. William Hurd of Cleveland's UH Case Medical Center.
Experts say the majority of women follow the same biological timeline, with fertility decreasing after age 35, making pregnancy difficult after age 40 and menopause finally hitting by age 55.
If the test is perfected it might allow women a little extra time for their childbearing years or encourage them to start a family before it's too late.