It's certainly not what I would have expected before seeing the data but we know that the TFR is highest for the least educated (no HS diploma) across all population groups.  This can be considered roughly equivalent to lowest IQ.  

The hypothesis I subscribe to is that most people can understand "I shouldn't have unprotected sex because I might get pregnant" but if you give them an out, people will think "Don't worry, I can get an abortion later" but the least intelligent will be less able to plan and execute that legal abortion and will suddenly find themselves 9 months later giving birth and wondering how this happened to them.

With the differing median IQs, Blacks had a proportion far enough on the left tail of the IQ bell curve to (temporarily) raise their TFR.  It had been falling prior to Roe vs Wade and eventually dipped below where it had been before. 

 Super insightful.

Thank you!