The 21-year-old revealed that she felt pressured when filming the scenes in question because there are such high expectations for the encounter between Stewart's Bella and Robert Pattinson's Edward.
"In the end, I didn't feel like we had filmed a sex scene, because we were both so uncomfortable and insecure, and because it's something very subjective," Stewart said, according to Mexican magazine 15 a 20.
"There's times when there's weird close-ups, and everybody has such high expectations for these scenes."
Stewart recently claimed that Edward sees his unborn child with Bella as "Satan's spawn" in The Twilight Saga: Breaking Dawn - Part 1.
Earlier this month, the actress vowed to work hard at keeping the details of her personal life private, confessing that she is frustrated at being the constant target of prying media.
> Twilight: Breaking Dawn releases new wedding, honeymoon pictures
The Twilight Saga: Breaking Dawn - Part 1 is due out in cinemas on November 18, followed by Breaking Dawn - Part 2 on November 16, 2012.