Using fetus outside of a conversation between doctors and/or nurses in a medical facility obscures the issue. No one else talks about their pregnancy like that. This was a reasonable change.
I can't think of a single instance when I or anyone I know have used the term unborn child. It's a loaded political term. They knew exactly what they were doing. It's also not reasonable at all when the actual text of the amendment uses the term fetus (you know, the language that would actually be adopted into the state constitution if passed). It's a medical procedure. The summary distorts and omits important information. There's no reason why they couldn't have put the full text of the amendment on the ballot other than the fact that those with the power to do so wanted to tilt the playing field to their side.
I've heard non-political ads for pills warning against pregnant women taking that pill because "it may cause harm or death to an unborn baby". That ad certainly wasn't intended to convey a message about abortion. Most people don't actually call it a fetus, instead a baby.
That's because in this context those women intend to carry the pregnancy to term. It's not the same thing.