"What an amazing year you've had!" the organization Tweeted following the Fashion Star judge's announcement on Tuesday.
Simpson – who lost more than 50 lbs. with Weight Watchers – "will not be following the program during the pregnancy while her weight and well-being are monitored by her obstetrician, as is recommended for any woman during pregnancy," Weight Watchers says in a statement.
The statement adds: "After she gives birth, Jessica and her doctor will decide when she may resume following the Weight Watchers program."
The organization also released a new television advertisement on Wednesday with Simpson sharing the news of her second pregnancy with viewers.
In the spot, the 32-year-old, who gave birth to daughter Maxwell seven months ago, reveals her new body.
"This year is all about new beginnings for me. I lost over 50 pounds on Weight Watchers and did not have to be perfect to do it. Being healthy has become a part of who I am, which is great timing because I'm having another baby," she says. "I feel like I'm on top of the world!"
In a statement released Wednesday, Weight Watchers' Senior Vice President of Marketing Cheryl Callan praised Simpson's efforts.
"We've seen first-hand that Jessica has a refreshed outlook on food, activity and the importance of developing healthy habits, which we hope will guide her through this next pregnancy and beyond," she said. "She has come a long way and we know her story and success will continue to inspire others."