Why does fertility decline with increasing age?

Egg quality: As a woman ages, her eggs decline in number and quality. There are changes in the chromosomes and dna that result in more abnormal embryos, infertility, and miscarriage.

Female fertility: A girl is born with every oocyte she'll ever have . Unlike men who produce new sperm regularly, females lose eggs from birth on; by ovulation, eggs getting 'old, ' and programmed cell death. Besides losing eggs each year, it is believed oocytes lost or used earlier in life are healthier or more fit for conception than the older ones. Thus both egg number and quality drops every year.