Fitness expert shows how moms can flatten the stomach post-pregnancy

— -- New mothers are turning to an exercise method to help beat the so-called "mummy tummy," the stubborn post-pregnancy stomach bulge that is often the result of a medical condition.

"What's causing the bulge is the pressure from your internal abdominal cavity, so whenever you strain or do certain positions you would see bulging through," Dr. Fahimeh Sasan, an obstetrician-gynecologist at Mount Sinai Hospital in New York, told ABC News of the common postpartum phenomenon.

During pregnancy, the growing uterus stretches out of the abdomen, which can cause the vertical bands of muscle that meet in the middle to separate from each other. For many women, this stretching in their post-pregnancy belly is actually a medical condition called diastatis recti, commonly referred to as abdominal separation.

Sasan said one possible way to prevent abdominal separation is "being active prior to becoming pregnant ... which we recommend for pregnancy anyway."

"Doing some sort of exercise, particularly core-strengthening exercises, before getting pregnant could be a good way to prevent this," Sasan added.

Fitness expert Leah Keller has developed her own technique, called the Dia Method, specifically to help new mothers afflicted with abdominal separation after giving birth.

Keller described diastatis recti as when "your six-pack muscles physically stretch sideways."

Keller told ABC News that a simple way to tell if you have diastasis recti is to lie flat on your back with your knees bent, then put your fingers right above your belly button and press down gently. Next, lift your head up about an inch while keeping your shoulders on the ground. If you have diastasis recti, you will be able to feel a gap between the muscles in your abs that is wider than an inch.

To develop the Dia Method, Keller teamed up with a doctor at Weill Cornell Medical College and observed 63 women with abdominal separation doing her workout routine for ten minutes a day over the course of 12 weeks. Keller says all of the women showed significant improvement in combating the post-pregnancy belly bulge. Despite her results, many experts say more research needs to be done, but agree that these exercises can give women a head start on losing stubborn belly fat.

Here are Keller's top exercises to help flatten the post-pregnancy mummy tummy:

1. Waist cinchers

This move works the transverse abdominis, your natural corset, and the entire length of the rectus abdominis, or your six-pack muscles, according to Keller. Lie on your back with your knees bent and put one hand behind your head and the other rested right on top of your belly button. Slowly nod your head, neck, and upper body up, using your abdominal muscles, and then return to resting, and repeat.

2. Alternating leg lifts

This exercise works the lower abdominal muscles as well as the inner thigh muscles when performed with a turnout move. Keller describe it as "the alternative to the double leg lift," saying, the "double leg lift is just too much of a workload to ... manage with safe activation." To do this exercise lie on your back and bend one knee while having the other leg extended straight out in front of you. Slowly raise the straight leg off of the ground.

3. Modified cobra

This move gently lengthens the rectus abdominis muscles without separating the abs, according to Keller. Roll onto your stomach and come up onto your elbows. Let your hips anchor you into the floor and dig your elbows into the floor, then pull yourself forward and up slightly without opening your upper abs.

"It is a much smaller move than a full cobra, and it's a very conscious, very targeted, gentle lengthening of the abdominal muscles," Keller said of the modified cobra.