Researchers have discovered a clue as to why older women experience more difficulties when conceiving.
An increased risk of infertility, miscarriage and birth defects are widely acknowledged for women who want to have children later in life.
However, scientists at Newcastle University claim to have come closer to explaining why this is.
Abnormalities are frequently down to the fact that the eggs of older women contain the wrong number of chromosomes.
Now the scientists have discovered that declining levels of proteins called cohesins are responsible for this.
The research published in Current Biology found that cohesins are essential for chromosomes to split evenly when cells divide, hence explaining why the eggs of older women can prove problematic.
Dr Mary Herbert, reader in reproductive biology at the Institute of Ageing and Health, based at Newcastle's Centre for Life, said: "The aged mice we used are equivalent to a woman in her early forties.
"Cohesin levels were very much reduced in eggs from older mice and the chromosomes underwent a very messy division resulting in the wrong number of chromosomes being retained in the egg."