'Skinny Mom' Sarah Stage Debuts Insanely Toned Abs a Week After Giving Birth

— -- Super fit model Sarah Stage spent nine months showing off her insanely toned pregnancy body on Instagram. Less than a week after giving birth, pictures show she’s already bouncing back.

“4 days post baby, total pregnancy weight gain was 28 pounds. I'm excited to resume my workouts in 5 weeks!” the California woman wrote next to an Instagram picture of herself in lingerie just four days after giving birth. Her abs, especially, looked sculpted and defined.

Her 1.3 million Instagram followers are amazed.

“Sara let me tell you have my full respect!!! You have showed the world that you can still be fit while pregnant…” one follower wrote.

“People should learn from u,” another wrote.

Stage did not immediately respond to ABC News' request for comment.

Dr. Jennifer Ashton, ABC News medical contributor and a practicing obstetrician and gynecologist, said she predicted Stage’s body would snap back into shape very quickly.

“She was in excellent shape to start,” Ashton said. “She exercised before her pregnancy and all throughout her pregnancy and she ate well.”

At 8 pounds, 7 ounces, Stage’s son, James Hunter, was no lightweight. But Ashton said because Stage had gained the appropriate amount of weight, she could see her belly would flatten out quickly. It also helped that she is still young and this is her first baby, Ashton added.

And should Stage choose to have another baby, Ashton said she saw no reason why she won’t look just as good the second time around.

“If she does things the way she’s doing them now, there’s an excellent chance things will turn out exactly the same way,” Ashton said.