But the the weight-loss company said in a statement that the pregnant star will continue to be their spokesperson, reported Ace Showbiz.
"The singer 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," a company representative said.
"After she gives birth, Jessica and her doctor will decide when she may resume following the Weight Watchers program.
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," it added.
Simpson gave birth to her first child with Eric Johnson, a baby girl named Maxwell, in May this year.