Women find it difficult to have children later in life because they are all but out of eggs, scientists have discovered. Though women are born with an average of 300,000 eggs, their ovarian reserve declines far faster than previously thought, according to the study from the University of St. Andrews and Edinburgh University. By age 30, a woman has only 12% of her eggs left; by 40, that dwindles to just 3%.
Though those women are still producing eggs, that dramatic decline has a major effect on their fertility, the doctors said. The research also revealed that the size of any given woman’s reserve can vary greatly; some had more than 2 million eggs, others as few as 35,000.