The 'Someone Like You' singer is said to have kept her pregnancy secret long before making an official announcement on June 29.
"Adele has barely left the house in recent months, so she could keep this to herself for as long as possible," an insider told Heat.
"She stopped exercising a few months ago, and since then it's been all about the baby."
It has been claimed this week that Adele is already working on her third studio album, but may put off its release for a few years so she can be "a normal mum".
"The last thing she wants is for her kid to become a celebrity baby or media commodity," a source said.
"Being a good mum is a lot more important to her than selling records and she's made it clear her priorities have changed now she's pregnant."
Adele has also apparently recorded a CD of nursery rhymes that she plays to her unborn child.
Watch the video for Adele's 'Rolling In The Deep' below: