Clinical evidence shows that above the age of 40 years, the risk of having a spontaneous miscarriage may exceed 50%!
You are born with the eggs that you have. The numbers deplete with time and obviously due to the aging process, the risk of abnormalities in these eggs increases with time. Therefore, as age increases, the number of eggs reduce, the quality of remaining eggs reduce and the risk of these remaining eggs having abnormalities increases. All this contributes to grossly reduced fertility and if pregnancy occurs, increases the risk of either miscarriage or abnormalities in the pregnancy.