How are newborns with down syndrome produced?

Oocytes that are released from ovaries during the last few months nearing the age of menopause at 40 – 50 years old have lesser ability of division as it has diminished till now. Owing to this, they could not complete proper meiotic division. Now, if these oocytes are fertilized, the newborns created from them may have some abnormalities such as Down’s syndrome.