21 was famously based on the singer's break-up from her ex-boyfriend, but the new LP is said to reflect her excitement about becoming a new mother.
An insider told Us Weekly: "It will be lighter than her last ode to [a] break-up. The pregnancy has had a big impact on her songwriting."
The source added: "She is lying low and focusing on becoming a mum. The baby is healthy and she's so excited."
The 24-year-old has enjoyed unprecedented success since the release of her previous album, in the process breaking seven world records for US and UK digital sales.
The singer is rumoured to currently be recording the Bond theme for the upcoming Skyfall at Abbey Road Studios.