The 27-year-old has alleged Gaga is covering herself up these days the way only pregnant women do, reported Sun online.
"I think she is pregnant because she has been covering up this part of her body recently and I have been noticing that a lot," Osbourne said.
"And her style has changed and you can't bleach your hair blonde when you are pregnant," she added.
Gaga is currently dating 'Vampire Diaries' star Taylor Kinney.