Carrie Underwood gave birth to her first child just three months ago, but she has managed to successfully lose weight and get her pre-pregnancy body back.

The former "American Idol" winner and her husband, NHL player Mike Fisher, welcomed their son Isaiah Michael Fisher into the world February 27.

Erin Oprea, the Grammy award-winning country music star's personal trainer, revealed Underwood's full workout regime: "We do lots of lunges, squats, plyometrics, stairs, pull-ups along with weight training. The key to the success is keeping all of this at your level and not to do too much too soon. Listen to your body," she said in an interview with E! Online.

As for Underwood's flat and toned stomach, Oprea said: "Core exercises are great to help tone the body, but a slimmer midsection is truly made in the kitchen. Eating clean is the fastest way to get flatter."

The singer herself revealed another secret to her workout regime: her own fitness clothing line Calia.

"I created Calia to make it easier for me and all other women to work in working out," she wrote on Calia's official website.