Todd Williamson / Invision/AP 1 / 18
Todd Williamson / Invision/AP 1 / 18

The last time Megan Fox appeared on "The Tonight Show With Jay Leno" in February, the 26-year-old actress was hiding a small baby bump.

"I was about two months pregnant. I was really sick," the star of "This Is 40" said when she returned for the Dec. 18 episode of the NBC talk show. "I was very nauseous. I had really bad morning sickness."

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Fox continued, "It was so bad for me. ... I was convinced that I was, like, maybe birthing a vampire baby like the one in 'Twilight' -- you know what happens to Bella, where she's in cold sweats all the time -- and I felt like that was happening because I had no vitamins and nutrients, and I was just nauseous."

"Something not human was happening!" she added.

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Luckily, Brian Austin Green's wife of two-and-a-half years didn't suffer for long. "The first trimester was really rough, and then I got to about 12 weeks and then it was fine," the actress said. "It was really a perfect pregnancy after that."

Fox -- already stepmom to Green's son Kassius, 10, from his previous relationship with actress Vanessa Marcil -- also opened up about giving birth on Sept. 27 at Cedars-Sinai Medical Center in Los Angeles. (Coincidentally, Reese Witherspoon and Jim Toth welcomed a son, Tennessee, at the same hospital that same day.)

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"I thought I was going to be tough and the nurses would be like, 'She's a warrior princess! She doesn't need an epidural! She's amazing! We're such big fans!'" Fox admitted. "As soon as I got out of the car, I was already crying for an epidural. I was asking the security guard for an epidural!"

"This Is 40" is in theaters Friday, Dec. 21. "The Tonight Show With Jay Leno" airs weeknights at 11:35 p.m. on NBC.

This article originally appeared on Usmagazine.com: Megan Fox: Why I Thought My Son Noah Might Be a "Vampire Baby"

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