Jessica Simpson stopped by "The Tonight Show" not only to promote her hosting gig on NBC's "Fashion Star," but also to open up about impending motherhood.

"It doesn't feel like I have a lot of time," she replied when Jay Leno asked when she expects to give birth. "Labor is really going to hurt. I have so much respect for my mom and all the women across the world.

This is a tough thing here, and I'm wearing six-inch heels today. It's a lot of weight to carry on six inches."

While Simpson was already engaged to fiancé Eric Johnson, she was still pretty surprised to find out she was going to be a mom.

"I was [surprised to find out I was pregnant]. We weren't trying, but we were practicing, and not safely practicing. I freaked out I was so excited," she recalled. "Eric ... was completely shocked. He had no idea I was taking a pregnancy test. He cried."

The pregnancy means that their wedding won't happen for a while longer.

"I want him to be my husband so bad. I do still want to wear the pretty gown and everything, and I have to wait till after the baby. Now she'll just be in the wedding," she said.

The conversation, of course, did turn to Simpson's nude Elle magazine cover, which paid homage to Demi Moore's similar shot for Vanity Fair in 1991. "I shot that a couple months ago. I don't quite look like that right now," the extremely pregnant singer said with a laugh. "I'm glad I did that a couple months ago. ... I can't believe [the Moore cover] was 20 years ago. I don't think I saw it when I was ten-ish, but I think through the years I saw the iconic pregnant shot. I wanted to do it. Elle didn't even ask me if I wanted to do it. I just always had the idea in my mind that I would do it.

"I don't think [my dad] would have recommended it. No, it was a private set," she continued. "I don't even know if I told him. Maybe my publicist did, but my pub is one of my really, really good friends. I just said I wanted to do it and we don't have to tell anybody about it so everybody's pretty shocked about it. I haven't had a conversation with him about it. He is backstage so it makes for an awkward conversation afterwards."