On average it’s in the 40’s, and fertility for most women is very low at 45 and older with their own eggs. There are many individual factors however – we see women in their 20’s who can’t conceive naturally, and there are healthy pregnancies in 47 year olds, and everything in between. Using egg donation there may be no biological upper limit but risks are higher in the 50’s: women 55 and older should not try to conceive.