I honestly wouldn’t know where to start looking for data on that. But I didn’t make the claim that this was definitely going to happen, just that it was the likely outcome, based on the common sense assumption that if abortion access wasn’t easy, safe, and anonymous, and involved a significant risk of injury or death for the mother, more women would likely find it less risky to carry their pregnancy to term and give up the baby for adoption if they haven’t changed their mind on it by then.
Also, they may simply choose to use birth control more often, and/or insist on their partners wearing a condom.
From my point of view, I find the claim that making abortion illegal would not prevent even a single one from occurring far more incredulous and therefore requiring a higher level of proof.