When I received my I600A (approval from immigration), the form said I was approved for a girl. But actually I'm leaving that up to fate -- I couldn't have chosen boy or girl if I got pregnant, so I'm not going to choose now.
At first I was worried that it was going to be a big deal to get it changed, or slow things down. But one phone call to USCIS in Texas, a return phone a week later asking me to fax a copy of my approved home study, and then one week after that it arrived. Yesterday in the mail was my newly amended I600A for "either male or female."
Hooray for speedy government agencies. How often can you say that?!