Adele is reportedly due to give birth in September.
The Someone Like You singer is seven months pregnant by boyfriend Simon Konecki, but has hidden her bump from the public by keeping a low profile and wearing baggy clothes.
A source close to the singer says that the couple wanted to keep their happy news a secret for as long as possible to avoid attention.
A source told heat magazine: "'Adele has barely left the house in recent months, so she could keep this to herself for as long as possible.
"She stopped exercising a few months ago, and since then it's been all about the baby."
Other friends say 36-year-old Konecki — who has a five-year-old daughter from a previous marriage — and Adele (24) have been keen to have children since they started dating last year.
Another source told LOOK magazine: "Family is very important to them and they've been talking about kids and getting married since they met last September. I think Adele's still quite surprised at how quickly it happened, though.
"She's clearly got the usual nerves of an expectant mum, but Simon's been amazingly reassuring, they're both so happy."
It has also been rumoured the couple could have married in secret, after Konecki was seen wearing what looked like a wedding ring when he attended the Ivor Novello awards with Adele earlier this year.
Adele revealed her pregnancy to her fans on her website in June, writing: "I'm delighted to announce that Simon and I are expecting our first child together.
"I wanted you to hear the news direct from me, obviously we're over the moon. Yours always, Adele."