@Joseph
I would not support such an amendment. I do not believe that the legislature should violate separation of powers by passing legislation to overrule decisions if the court.
This is probably not the reason you thought would govern my opinion. The Court changes over time and state decisis is not absolute; Dred Scott, Plessey v. Ferguson are two glaring examples. If the country truly swings to oppose non-medically required abortion the court will react over time.
#2 It is very easy to get a doctor to say something is medically necessary and sidestep your proposed amendment.
I know many people whose doctors were happy to sign handicapped parking permit applications or excuses from gym class