But past year, on "Ellen", Simpson said, "We got an IUD, nothing's gonna get in that uterus".
The newest addition is a girl, she added.
Earlier this year, Simpson admitted that she had "baby fever" and that she and her hubby "always practice".More news: Champions League: Messi hat-trick fires Barca to victory over PSV
Jessica has been subject to baby rumors for the past few years.
In a second Instagram post, pink balloons were revealed with her kids celebrating in their backyard. Says Simpson, "This little baby girl will make us a family of five". You know that kid is going to be so cute!
Simpson told Ellen DeGeneres previous year that she and Johnson weren't planning to expand their brood.
She said: 'Being a mother is the best opportunity and challenge I've ever been blessed with in life.