I can imagine several paths - criminal, civil, or administrative - for the GA definition to get to the supreme court.
And then, taking the definitions in from O.C.G.A. 1-2-1 as posted by YAV, and plugging into the 14th as posted by Sentinel: "All human beings including an unborn child born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside."
All it would take is one case from one GA resident appealing an IRS criminal or administrative sanction for claiming their fetus on a federal tax return. Or a child support case involving a fetus impregnated in GA and the mother moving to another state.
The SC can't change the wording of the 14th, but the court could certainly affix additional definitions or interpretations to specific words in the 14th.