I haven't written a novel, but I've written fic and a doctoral thesis and managed a project or two I was proud of. And I've had two babies, and... having a baby isn't ANYTHING like any of those things. Having a baby is hard work, sure, and really cool, but... largely instinctual in a lot of ways. (I mean, I didn't really think too hard about my body working to grow the embryo. It really kind of just did it itself.) Writing (for example) is a much more conscious crafting sort of thing.

I'm a little more okay with the idea of parenting as a metaphor, at least in terms of conscious and continuing interesting effort -- except that, of course, the child is its own autonomous entity rather more than my thesis was.