On Christmas Day, the 32-year-old star confirmed her pregnancy after she posted a picture of seven-month-old daughter Maxwell sitting on sand above the words 'big sis'.
Simpson, who is currently on holiday in Hawaii for the festive period, has since posted an image of her bare stomach with the caption: "Bumpin' and Proud!".
Although she did not disclose how many months gone she is, Simpson appears to be in the later stages of her pregnancy.
The Dukes of Hazzard star and former NFL star fiancé Eric Johnson began dating in May 2010.
The pair got engaged in November the same year following Johnson's divorce from ex-wife Keri Johnson.
Simpson, who is the face of Weight Watchers in the US, faced family problems this year when her parents filed for divorce.
Father Joe Simpson has since denied rumours that he is gay.