Well, there's no causal chain from what the pregnant woman thinks to what the child remembers, or at least, no chain of the kind that we associate with future selves. Who knows, maybe in the future there will be a memory enhancing modification, without which our natural memories would seem fairly distant from continuation.

What basis have you for expecting to perceive waking up as the copy in the future?

I'd expect the same as if I were to e.g. somehow reset my memories to what they were 10 hours ago. I would definitely not expect subjective continuity with my current self in the case of memory reset - I wouldn't think it'd be such a big deal though.

There are other possible explanations than causal chain, e.g. persistence of computation,

It seems to me that something like that could break down once when we try to define what we mean by persistence of computation, or indeed, by computation.