"Don't worry, Dave, it's not yours," the singer joked.on Tuesday

"Oh. Well, I think that's good news for both of us," Letterman responded.

"So, we've established now that you are, in fact, pregnant, is that right?" asked Letterman.

"Yes sir," Spears replied.

Spears insists she would never neglect her children because of work.

She says, "I genuinely love to sing and dance. When I get in a creative mood, I can't shut up. It's the craziest thing.

"At one point I was thinking of being a home mom, but when my son sees me dance he lights up. Then I know what I'm supposed to be doing - if Mom's happy, baby's happy!

"I've been meeting with different people to work on the album and looking at different (movie) scripts.

But I've mainly been concentrating on my son."

Spears wed Federline in September 2004, and the pair began talking about starting a family soon after. "I can see myself as a mom. Next year at 23, I am so there," she told PEOPLE shortly after the wedding. Just four days short of the couple's first wedding anniversary, she had accomplished that goal.