A genetic advantage allows some women to give birth over the age of 45, say researchers.
According to Israeli researchers, the reason some 45-year-olds easily have a baby while much younger women have difficulty conceiving could all be in their genes.
Although naturally conceiving a child past the age of 45 is rare, a genetic advantage appears to allow some women to do so, and Dr Neri Laufer of the Hadassah University Hospital in Jerusalem has discovered that some of those older mothers have a distinct genetic profile.
At meeting of the European Society of Human Reproduction and Embryology in Copenhagen this week, Laufer said his team had found a select group of genes that were significantly different.
Using gene chip technology, he and his team compared the genetic profiles of eight women chosen from 250 who had had children past the age of 45 with profiles of six others who had finished their families by the age of 30.
According to Laufer these women appear to differ from the normal population due to a unique genetic predisposition that protects them from the DNA damage and cellular ageing that helps age the ovary.
Conceiving naturally past the age of 45 is rare because a woman's supply of eggs diminishes as she ages and approaches the menopause, which normally occurs around the age of 50.
The women in the study were Ashkenazi Jews, who are descended from the Jewish communities of central and eastern Europe, most had had six or more children, did not use contraception and had a low miscarriage rate.