I think you are thinking of IV Sent d. 31, in the exposition, where it is stated that "they who procure drugs of sterility are not spouses, but fornicators. This sin may be exceedingly grave, and to be reckoned among wickednesses, and against nature ... however it is less than homicide". This is hardly a license to abort.
I never said that St. Thomas in any way condoned abortion. I just said he was mistaken on when life begins.