The 17-year-old actress checked into hospital this morning, where she was joined by close family and fiance CASEY ALDRIDGE, 19.
According to People magazine, the couple have named the tot Maddie Briann.
A source said: "Just the family were there.
"Everyone is healthy and happy."
Britney flew back to Jamie Lynn’s hometown of Kentwood, Louisiana, yesterday to make sure she didn’t miss her sister's big day.
She was accompanied by her dad, JAMIE, and brother BRYAN.
Source: TheSun, Picture: Splash