I've had dwarves give birth... while shooting at goblins. Seriously, there is something wrong with that.
But more on topic, I once had a dwarf give birth, cancel task to find her baby, pick up her baby (i guess when they give birth, they just sort of plop out onto the floor or something), and then be seized by a fey mood.
The story continues. The fey mood required a metal that did not exist in my stocks or map (to my knowledge). Baby and mother waited around in the forge for a while. Eventually mother goes insane, drops baby, and flings self into magma. Father is both despondent and ecstatic, due to a satisfying recent acquisition (decadent drink probably helped too). Baby sort of lies there for a while hungry and thirsty... it crawls around. Medic dwarf brings it a bucket of water. Baby continues to crawl around miserable, until it manages to find itself into a room, where i 'euthanize' it.
Another time, same general story, except mother goes berserk, beats baby, and then is killed by marksdwarf and war dog. Baby has red wounds and dies shortly thereafter. Talk about a bad day for that baby.
A nursery would be nice for de facto orphans... although I feel it's worth noting that, as it is, you can assign a bedroom to a baby... it will try to make it's way there where it will basically function as a resting/injured dwarf. I don't know if they can still grow to child/adulthood that way... as I said, I eventually euthanized the baby i got into a bed room (via assigning) since it was just always despondent and tying up medics and such (by euthanize, I mean I locked the door and waited =p)