There is no known case of any mammal that does not breath being conscious. Motion and reactions observed in sleeping human beings (totally unconscious) are much more sophisticated than anything detected in the unborn at any stage. Reactions and movement, in themselves, are not indicators or consciousness. There is absolutely no reason to suppose the unborn have any level of consciousness at all until they, "wake up," that is, begin to breath.
Actually, sentience and cognition are recognized responses in pre-born humans. This page [
Human Sentience Before Birth] gives an extensive look into this area (showing that consciousness may exist at rather young ages, even as young as 10 weeks [
Anatomical and physiological development of the unborn child]).
As for the fetal respiration (breathing), it starts when the umbilical cord exchanges O2 with CO2 between the fetus and mother. The mechanism's different (umbilical cord instead of lungs), but it's the same general process: Breathing (respiration).
-The Hajman-
consciousness may exist at rather young ages ... Well, anything is possible, but this much is certain, it is absolutely impossible to objectively know, not only if the unborn are conscious, but if any living creature in the world is. Consciousness in others is assumed on the basis of their testimony (but a very clever machine that appeared to be human could be made to make the same claim). In animals, it is presumed, because their behavior is what we would expect if they were conscious. As for evidence of the consciousness itself, since in all creatures it is a subective experience, their is no evidence. The only consciousness you will ever know is your own.
It is bad science to attribute behavior to something when all that behavior can be explained without that attribution, and the thing it is being attributed to can never be known.
Of course, scientists with an agenda, often are less rigorous than they ought to be.
Hank