Older eggs are more prone to forming embryos with either too many or too few chromosomes. This is the reason why older women have a greater rate for infertility, miscarriages and babies with chromosomal birth defects

https://www.ivf1.com/age-birth-defects/

SMV for a woman is partly based on fertility.

Women ages 35-39 will deliver 1 to 4 additional cases of congenital heart defects per 1000 births. In age 40 and over, that number jumps to 30.