Once you conceive, and you get past the first trimester miscarriages.

http://www.babycenter.com/404_what-are-the-risks-of-having-a-baby-if-im-35-or-older_3127.bc

Once you conceive, and you get past the first trimester miscarriages, you face a higher risk of conceiving a baby with a chromosomal problem. This risk goes up every year.