(WUSA) -- A new study from the University of St. Andrews and Edinburgh University estimates the human ovarian reserve.
British researchers say the average woman starts out with 300,000 potentially viable eggs. She steadily loses that reserve. By age 30, nearly 90 percent have been lost. And by age 40, only 3 percent are left, with a higher proportion of abnormal eggs.
Endocrinologist Dr. Robert Stillman with Shady Grove Fertility in Rockville says the new research is a wake-up call.
Dr. Stillman says, "The study emphasizes that there is a loss for reproductive potential, an earlier loss of eggs, than we had thought."
"The new information is that the decline may occur earlier, and that their family planning needs to be considered earlier. Women need to be empowered by that information, and make valid choices based upon it."
But some of the women 9NEWS NOW spoke with were shocked, and even skeptical of the sense of urgency this new analysis conveys.
Cindy Fitzenmaier says, "I know I still want to be a mom... and I think it is totally possible."
Christine Steward adds, "I think a lot of us want to delay that as long as possible, and achieve what we want career-wise and socially."
And then there are women who said other considerations temper the ticking of that biological clock.
"I'm in my thirties. And finding a man you can raise children with is the most important thing, and I haven't found that person yet. If that comes along, then I will be blessed to have children. But if not, there's adoption," explains Melissa Whitworth.
And Dr. Stillman says this study should not be taken to mean fertility drops off dramatically at age 30. It is a gradual decline, and many couples still conceive without problem. But he says women need to realize biology doesn't offer an endless window for childbearing, so they aren't painfully disappointed years later.