Serena Williams talks about sleeping while pregnant with Self Magazine.

Williams, who represents Tempur-Pedic (she says she has used their mattresses for almost 10 years), knows the importance of a good night’s rest. Quality sleep has been essential for her tennis career, she tells SELF, but it’s taken on a whole new meaning as of late. “Now that I’m in this pivotal part of my life, becoming a mom, sleep is even more important. I’m reading all these different blogs and articles and comments and these pregnant women are like, ‘I can’t sleep, I can’t sleep,’ and I totally understand what they mean,” she says, adding that when she travels, she sometimes even sleeps in a chair because being away from her usual mattress feels so uncomfortable.

Although Williams is typically one of those unicorns who can function on four to five hours of sleep a night (the National Sleep Foundation recommends adults get between seven and nine hours of sleep every day), pregnancy has Williams spending a lot more QT with her bed. “Now that I’m an expecting mother, I go to bed around 9:30 or 10 P.M., and I wake up around 6, 7 A.M. So I’m getting a lot lot more sleep,” she says.