OMG this is my favorite subject.
Could we get anywhere by asking when a developing human becomes conscious? That would occasion a lot of fights, but surely the frozen bundles of cells recently dropped in Alabama were (are?) not conscious, nor were they conscious before being frozen. (Ruling out panpsychism. If everything is conscious then nothing is conscious.)
But would anyone doubt that the baby that emerges from the womb is conscious? Only an extreme blank-slater maybe.
Along the way *something* happens. Not all at once, probably. But recalling my own children when they were in the womb, they began to indicate that they were aware of things going on around them, responding to music, that sort of thing. And music is uniquely human, unless you count the howling of canines* as a form of music. Some dog owners of my acquaintance say their dogs respond to music.
But something happens, and it seems to correspond to the developing baby beginning to *interact* with its world.
So we have, if I am not mistaken, arrived at Heidegger. Consciousness has to be *of* something; has to be embodied, interacting with its world.

* Someone is sure to mention whale song, so there, I just did.