Michiko’s suggestion to use “Do you know if it's a boy or girl yet?” is very good — We actually use “it” as a dummy subject (the pronoun “it” has no antecedent, so it doesn’t really refer to anyone or anything) in reference to anyone and anything that has not yet been identified. Once the baby has been identified, we should use the correct pronoun if the gender is known. Otherwise, it used to be common to refer to a baby of unknown gender as “it” (this goes back to Old English grammar), and you may still occasionlly hear that today, especially in American English. Nowadays, however, it sounds better to use singular “they”, as Michiko recommends.

No, I don't. I say "they" or "the baby." Example: What room are they going to sleep in? Example: What room is the baby going to sleep in? Sometimes I hear people combine the two. Example: Have you picked out a name for him or her? With certain questions, people will say "it." Example: Do you know if it's a boy or girl yet?

I will ask the parents. Sometimes though they don’t know the sex yet, they like to have a nickname by saying she or he. But for me personally, I’ll use they/them as neutral pronoun.