Even when you exclude women using fertility treatments, women who become pregnant in their late 30’s and 40’s are more likely to have twins when compared with women in their 20’s and early 30’s.

Why?

It has to do with the changes in hormone levels as you age. When a woman gets older, their FSH (follicle stimulating hormone) levels increase. Since this hormone is responsible for getting the eggs ready for ovulation, this increase leads to a greater chance of having twins.