Dan Steinberg, Associated Press
Molly Sims and daughter Scarlett May Stuber attend Tom's of Maine ‘Baby & Me’ yoga class in Los Angeles on Sunday, June 28, 2015. Sims and Stuber participated along with other new moms in a gentle flow class, led by Zooga Yoga, designed to help parents maintain a healthy lifestyle with a new baby in the home.

It's a postpartum nightmare for women: being asked when the baby is due after you've delivered.

But the "mummy tummy" that one-third of women have months after giving birth may not be a sign that they're eating too much. It could be diastasis recti, a separation of the abdominal muscles that can occur during pregnancy.

As Michaeleen Doucleff of NPR recently reported, the condition is a common side effect of pregnancy caused when the growing baby pushes against the rectus abdominus, a flat sheath of muscle that runs from the pelvis to the sternum.

"These are the muscles that give you a 'six pack,'" Dr. Linda Brubaker of the University of California, San Diego, told Doucleff. "People think these muscles go horizontal across the belly. But they actually go vertical from head to toe."

Before pregnancy, a cross-section view of this muscle would show a pair of muscles on either side of the belly, meeting in the middle at tissue known as the linea alba. After pregnancy, however, in some women, there's often an inches-wide split, which can be felt by palpitating the area around the belly button with your fingers.

The gap can close on its own, but if it doesn't, organs and tissue can protrude, causing a woman to still look pregnant even if her baby is already eating solid food.

This is not just a cosmetic issue, Doucleff wrote. Women can start to experience lower back pain and in some cases, a hernia can develop.

"If there's a defect in a layer of tissue called the linea alba, then the bowel can poke through. That's going to be more dangerous," Dr. Geeta Sharma of Weill Cornell Medical Center-New York Presbyterian Hospital told NPR. (Women who have been pregnant may remember having "linea nigra," a dark line that ran down their stomach; the linea alba is just under this line.)

Women with diastasis recti may also suffer from incontinence, and the condition may affect performance in athletes, according to K. Aleisha Fetters, writing in U.S. News & World Report.

"I regularly see firsthand the effects of (diastasis recti) on a woman's ability to function, whether it be leaking urine while she lifts weights in the gym or struggling with daily tasks like lifting her toddler or running to catch a cab," Karen Weeks, a physical therapist with the Northwestern Medicine Integrated Pelvic Health Program in Chicago, said in U.S. News & World Report.

Are you at risk?

Research published last year in the British Journal of Sports Medicine said about 60 percent of 300 new mothers studied in Norway had abdominal separation six weeks after giving birth. The percentage of women affected declined to 45.4 percent at six months postpartum, and 32.6 percent one year after giving birth.

That study involved first-time mothers, however, and diastasis recti is more prevalent in women who give birth to large babies or twins. You're also more likely to have it if you've been pregnant multiple times, or are older than 35. And, "most women who have a gap eight weeks following pregnancy still have it a year later," Fetters wrote in U.S. World News & Report.

While your doctor can diagnosis the condition, you may be able to tell if you have diastasis recti by doing a simple examination yourself.

According to NPR, the best way to do this is to lie flat with your knees bent, press into your stomach just above your naval, and lift up your head about an inch while keeping your shoulders down. "If you have diastasis recti, you will feel a gap between the muscles that is wider than an inch," the NPR report said.

If you have it, don't rush for the phone to call a plastic surgeon. Exercise may help. But some exercises, like some types of crunches, may also make the condition worse, so don't rush into a fitness program designed for non-lactating warriors.

To try to correct her own abdominal separation, NPR's Doucleff signed up for a class taught by Leah Keller, a personal trainer in San Francisco who specializes in fitness after childbirth.

Doucleff, and the other mothers in her class, saw improvement they attributed to one exercise done for 10 minutes a day.

How it's done

The exercise, developed by Keller and Sharma, was initially tested in a group of 63 women, some of whom did the exercise while pregnant, others after giving birth. All the women in the study showed improvement in abdominal separation, Keller and Sharma said in a study published in the peer-reviewed journal Obstetrics & Gynecology in 2014.

In the study, the women did the exercise for 10 minutes each day for 12 weeks.

The exercise involves extending the belly while inhaling, then contracting it while you exhale. Doucleff described it this way:

"And then as we exhale, we suck in our belly muscles — as far back as they'll go, toward the spine. … Then we take tiny breaths. With each exhale, we push our stomachs back further and further."

While it can be done in several different positions — cross-legged, standing with knees slightly bent, or lying on your side in the fetal position — two things are important: First, that your back is flat, not curved, and that your fingers are on your belly button, to ensure that it's not bulging forward, Doucleff wrote.

Does it work?

Doucleff, who has a Ph.D. in biophysics, said she did the exercise for 10 minutes daily for the four weeks of her class, and then for an additional three weeks after the class ended. During that time, her abdominal separation decreased from 1.2 to 0.6 inches, and she said she lost an inch from the circumference of her waist. Other women in the class completely closed up their abdominal separation and lost several inches around the waist, she said.

Doucleff's experience, of course, is anecdotal; she was not part of a study. And Sharma, the ob-gyn at Weill Cornell Medical Center-New York Presbyterian Hospital, acknowledged the dearth of research on the subject, and noted that her own study was small.

There are other exercise programs that are designed to correct diastasis recti, even some commercial programs that promise results but cost about $100.

Comment on this story

The American College of Obstetricians and Gynecologists does not suggest any specific exercise to restore abdominal tone, but recommends that women get 150 minutes of moderate aerobic activity (like brisk walking or riding a bike) each week after having a baby. ACOG also recommends Kegel exercises to strengthen the pelvic floor.

Of course, for many moms, having a different body after childbirth is a badge of honor, not cause for shame or embarrassment. But women who are experiencing lower back pain after childbirth, or those who plan to have more children, might want to invest a few minutes a day in the exercise.

"My abs are definitely firmer. And regularly doing this exercise brought a bonus benefit: My lower back pain has almost completely gone away," Doucleff wrote.