This model is about to hit the 9-month mark. So how are these abs possible? A prenatal fitness expert and ob-gyn weigh in
Sarah Stage Instagram

If it's hard for you to believe that the woman in this photo is eight-and-a-half months pregnant, you're not alone. The Internet has been going crazy ever since 30-year-old lingerie model Sarah Stage announced her pregnancy on Instagram last month with a photo showing off her defined abs and a barely-there baby bump.

Admittedly, we were curious too. So we asked an ob-gyn to break it down. Bottom line? "There's no obvious explanation. This is not what normal pregnancy looks like at 34-weeks," says Alyssa Dweck, M.D., and co-author of V Is for Vagina. But that doesn't necessarily mean it's unhealthy, she says. In fact, there are plenty of reasons to explain her surprising appearance.

"Some women don't show. The rectus muscles might be so well defined that they're masking her growing uterus," Dweck says. Not to mention, a lot of the way someone's belly looks during pregnancy depends on how they are shaped on the inside. Different pelvic bone structures may predispose you to looking different on the outside, she explains. Other variables include the way the baby is facing, the size of the baby, and the amount of fluid around the baby. Plus, Dweck adds, "when you have your first baby, your muscles will remain tighter and more defined until you deliver and until the rectus muscles have the chance to separate."

Pre- and post-natal fitness expert, Sara Haley agrees. "I actually don't think she looks unhealthy at all. If you look at a picture before she was pregnant, she was teeny tiny. She's definitely gained at least 20 pounds, which is what doctors recommend." And based on the look of her oblique muscles, she's clearly working out, Haley says. "The muscles I'm seeing on her are the ones that help support your growing baby, so that's not a bad thing. That's amazing, that's going to help her bounce back."

When it comes to exercising while pregnant, naysayers will probably always feel the need to weigh in, but as we've reported in the past (remember the nine-months pregnant woman who stirred up controversy for her CrossFit pics?), the two can go hand in hand, as long as you proceed with caution. "In general, exercise is definitely recommended if you were used to exercise beforehand. We usually tell people to moderate the intensity-75 percent to 80 percent of what they were doing beforehand," Dweck says.

She also recommends hydrating well, and keeping your pulse rate below 140 beats per minute, as well as engaging in activities you would normally engage in pre-pregnancy-i.e. don't decide to run a marathon for the first time! Haley also recommends avoiding putting too much pressure on the core, which can lead to ab separation or diastasis recti.

At the end of the day, only Stage's doc can know whether she's healthy or not. But as far as these experts are concerned, it's nothing to be alarmed about. "Props to her for being able to figure out how to be pregnant and still do what she loves to do," Haley says.