Carrie Underwood has revealed she often sings to her unborn son..

The 31-year-old singer and former "American Idol" winner revealed as much Monday on "The Tonight Show." Underwood may be a six-time Grammy winner, but the country star told host Jimmy Fallon she feels pressure to sing well when serenading her baby bump.

"He hears me singing whether he would like that or not," she related. "I mean, that's what I do, he doesn't have a choice. I do feel like I have to sing good all the time. Like, if I'm just in my car driving, I feel like I have to make it good because he's listening. He's always in there."

Underwood and NHL star Mike Fisher married in July 2010, and announced they are expecting in September. Fallon welcomed his second child, daughter Frances Cole, with wife Nancy Juvonen on Dec. 3, and shared the first photos of the newborn earlier in the episode.

Underwood released her fourth studio album, Blown Away, in May 2012. The record debuted at No. 1 on the Billboard 200, and includes the singles "Good Girl" and "See You Again."

The singer will release compilation album Greatest Hits: Decade #1 on Dec. 9.