So an adult has a toddler stage. That does not make a toddler into an adult.
You really ought to learn to read for comprehension. You are trying to assert that the foetus is a person. Saying of course, does not make it so. Describing the legislative councils of the developed world, numerous public and private organisations, health systems, judges etc as mentally retarded, doesn't make them so.
A foetus is not an independent individual. It is an adjunct of someone else, dependent on them to the point of parasitism.
Sentience is entirely relevant. You ask why I do not consider a foetus to be a person, then wave your hand at my answer as if that is somehow dealing with it. Sentience is how we define a person. If AI develops to the point of sentience, the AI will be a person. We accept fictional beings as persons based on their sentience. Sentience is vital. The foetus is at best pre-sentient, but for most of the time is ill-equipped to sense anything, let alone make sense of it. You wave away sentience, yet accept wholly fictitious concepts such as moral absolutes or unalienable rights.