Actress-turned-math wiz Danica McKellar and her husband, Mike Verta, are "bursting" to tell people that they are expecting their first child later this fall.

The former 'Wonder Years' star tells PEOPLE she's nearing the end of her first trimester and is "so excited" about being a mom. She initially put off finding out about the pregnancy because she was busy finishing writing her upcoming book 'Hot X: Algebra Exposed,' which comes out in August.

"I wanted to put off the [pregnancy] test because I didn't want any distractions. That only lasted a day -- I couldn't stop thinking about it and I caved! You can't try to put that off."