I was jokingly calling him/her "the zygote" for a while, as in "the zygote and I are STARVING." My husband works in medicine and he can be such an anatomy geek, so we thought this was hilarious.
Then he pointed out that now it's really a fetus, but I didn't like calling my baby "the fetus" because it sounded creepy, plus let's face it, "zygote" is a much funnier word than "fetus."
Lately I've been catching myself calling it "the kid" but more and more also by the boy name that's our current #1 pick. Somehow with each passing day, referring to the baby as him or by the boy name feels increasingly right.