She also reveals even more in the interview, saying pregnancy wasn't really on her mind when she found out she and husband Jordan Bratman were to become first-time parents.
"We were planning on starting to try after the [Nov. 2006-May 2007 Back to Basics] tour. And so, I had gone off the Pill to prepare my body, because I didn't know how much time it would take," the Grammy winner, 26, tells the magazine.
"You've heard it takes some time – except with Power Egg and Super Sperm here," she reveals, "I'm like, Oh, my God, can you believe it just happened?"
Aguilera believes the moment of conception occurred when Bratman – a music executive whom the singer married two years ago – visited Georgetown during a tour stop, when she had one month of physically challenging concerts still left to perform. (Her Washington, D.C. concert took place in early April – which could conceivably mean the baby's due in January.)
Physically ChallengingBesides hanging from a circus pinwheel during the tour, Aguilera also sported mega heels onstage.
"I was paranoid," she admits. "There are so many things that could go wrong – somebody could slip, somebody could fall, I could fall. There was no way in hell I was going to jeopardize my baby for my show."
Her solution was to wear a carefully hidden heart monitor that she kept secret from concert crowds. "I didn't want to make the audience uncomfortable, like, 'Pregnant lady onstage! Is she going to be okay?' But I had to announce it to my band and my dancers, because I wanted to make sure they had my back."
Paris Hilton's SpoilerHaving kept mum about her pregnancy, until she confirmed her condition to Glamour magazine (which reported it earlier this month), Aguilera is also asked if she was upset when, at an MTV Video Music Awards party in September, Paris Hilton publicly introduced her as "the most beautiful pregnant woman in the world."
With a shrug, Aguilera says, "Because I hadn't said anything, people thought I was trying to keep it this big, bad secret, and that's not the case at all. I just wasn't commenting. I'm not being like, 'Hey, everybody, I'm pregnant!' I'm not that girl."
Confrontational SexualityNow that the secret's out, Aguilera says she favors having a large family, though she doesn't have a specific size in mind.
Asked too how her "confrontational sexuality" might come into play with her parenting, Aguilera responds: "We're so labeled. If you're too sexual, you're slutty. If you're not sexual enough, you're a prude. I like to put it out there as a topic of conversation. Why does it bother you? What's your problem with it? Am I really hurting you? Let's get to the root of it."
When it comes to herself, she adds, "I have more than one side of me that likes to get out on a stage and sing. Sometimes I want to be aggressive, sometimes I want to feel empowered in my sexuality and my vulnerability. I want to put all that out there."