Not at all. A comatose man is a person who previously demonstrated human consciousness. A fetus is an entity that has never demonstrated human consciousness. The comatose man has a human EEG and a fetus less than around 30 weeks, I think, doesn't have one.
The comatose man already demonstrated his humanity, so we ordinarily have reason to treat him as someone who may do so again. The unborn have never demonstrated that humanity, though I myself grasp why viability and the emergence of a human EEG are significant markers.
I hope it's not lost on you how transparently arbitrary your determination here is.
To summarize: What's important is conscious awareness, perception, and communication. Except... OK... a comatose man who has none of these things gets grandfathered in, because he at one time had conscious awareness, perception, and communication, even though he lacks them now. And the fact that a fetus will imminently develop all of these things doesn't count because... well... it just doesn't. But of course a baby who has developed a nervous system after 30 weeks
does count as a human being, because despite never having experienced conscious awareness, perception, and communication, his/her having developed a nervous system overrides this fact.
In conclusion, this definitely all makes sense and isn't contrived so that we can insist the killing of unborn babies under 30 weeks old is morally acceptable despite admitting that killing comatose men and unborn babies 30 weeks or older is a terrible moral wrong.
Which is why it is not fit to be a person yet. Even a premie doesn't violate the rights or threaten the well being of any person, but an embryo/fetus can - if the woman didn't consent to pregnancy in advance.
Hence, 'A fetus "is not fit to be a person" because it can't control where it gestates.' is your argument?
Where in any extant law--moral, ethical, or civil--does an individual's ability to select his/her location or situation in life determine his/her "fitness to be a person"? (Excepting abortion, of course, since it's what's being debated.)
The answer is: Nowhere. The notion was blessedly thrown out with the idea that people of certain races are unfit for personhood, that people of lesser intelligence are unfit for personhood, that people of lesser status are unfit for personhood, etc.
A moral society does not determine the value of a human life based on its relative fitness, and
especially not fitness based on factors completely beyond an individual's ability to control.