The duchess of Cambridge's comments came Sunday as she handed out sprigs of shamrock to members of the Irish Guards at an annual St. Patrick's Day ceremony in Aldershot, People reported.
Sgt. Thomas Laven, who received a long service medal, said he congratulated Middleton on her pregnancy.
"I congratulated her on the impending birth and said you've got sleepless nights to come," Laven said. "She said she was prepared for it."
Lee Wheeler, another guardsman who spoke with the duchess at the event, said: "I asked her do you know if it's a girl or a boy and she said not yet. She said, 'I'd like to have a boy and William would like a girl.' I asked her if she had any names and she said no."