'A prognostic test would be helpful. Women want to know this. It's very important information. If you are planning your career, you need to know when to stop and come out and have kids.'

In a study presented Tuesday at a European fertility conference, scientists reported some women who find it easy to conceive after age 45 have a special genetic profile.

Scientists always suspected genes must help those rare "superbreeders" to defy the odds and get pregnant over and over again late in life, but this is the first time it has been proven, said Dr. Hans Evers, former chairman of the European Society of Human Reproduction and Embryology.

Evers, who wasn't involved in the research, said the findings could help women avoid the disappointment of discovering too late that they have become infertile.

The Right Profile

"It doesn't work if you tell all the women in the country that they should have their babies in time because they don't feel it pertains to them. But if you can say with a test, 'You personally are at high risk of infertility by 35,' then that would work," said Evers, a professor at Academic University in the Netherlands.

Similarly, he said, test results indicated the right profile could reassure the rare woman who can afford to stretch the timeline a few years.

For most women, fertility gradually declines until age 37, after which it plummets.

In the study, Dr. Neri Laufer from Haddassah University Hospital in Jerusalem, selected from a group of 250 Ashkenazi Jewish women who gave birth after age 45.

Most of the women already had at least six children and rarely suffered miscarriages, which the researchers felt indicated they might have a natural ability to escape the aging of the ovaries.

The researchers looked for differences in the genes between eight women who had conceived after 45 and six women of the same age who had their last baby by age 30.

They found blood samples from all eight women who became pregnant after 45 had a unique genetic profile that did not exist in the other women. Less than 50 genes were responsible for the difference. They all tended to protect against DNA damage and early cell death, which both age the ovaries.

Laufer said he found the same genetic fingerprint in a similar study that he later conducted on Bedouin women. He did not present details of those results.

More Eggs to Start With

Pregnancy after 45 is rare because the number and quality of eggs depletes. Girls develop their lifetime supply of eggs by the age of 7 months and throughout their lives the eggs mature and die.

Bill Ledger, professor of reproductive and developmental medicine at the University of Sheffield in England, said it makes sense that the genetic pattern seen in the Israeli study might slow the aging process in the ovaries, thereby making pregnancy possible at later ages.

"What would be happening in these women is that they have more eggs to start with as children so they work through their lifetime supply more slowly. And if these women have a slower rate of loss, they are going to carry on longer," he said.

"A prognostic test would be helpful," if the research findings are shown to apply to women everywhere, Ledger added. "Women want to know this. It's very important information. If you are planning your career, you need to know when to stop and come out and have kids."

Tests that can tell women vaguely how long they have until menopause are already on the horizon. They are imperfect, but adding a genetic test would allow doctors to guess more accurately, Ledger said.

"Right around the corner is hormone testing that gives you some idea of how many eggs you've got left. Do that when you're 30, again when you're 32 and again when you're 34. Plot your individual graph and if it's declining you need to stop doing what you're doing and have your family," he said.

"On the other hand, you may push it a bit longer if your levels are nice and high, but not too long."