I'll source -- http://www.pewsocialtrends.org/2015/05/07/childlessness/

15% of women ages 40-44 in the USA have never given birth, from which we can pull 85% of women ages 40-44 have given birth, as of 2014.

Wow, I got it right to a percentage point? I didn't realize it was 40-44, so maybe it moves teensy bit with IVF past 44. Thanks a lot for the cite.