There's no question Kylie Jenner's body is back and better than ever. Less than two months after giving birth to daughter Stormi Webster, the 20-year-old is already rocking a bikini! But just how did she drop the pregnancy pounds so quickly? She revealed her answer on Monday, March 19, by posting a pic of herself wearing a Waist Gang Society waist trainer, and some people aren't pleased. Check out the video above to see the pic — and what a certified OBGYN has to say!

"My girl @premadonna87 hooked me up with the @waistgangsociety snap back package. #ad waistgang has the BEST quality snap back products," the makeup mogul wrote in her caption. "Make sure you get your package & follow @waistgangsociety to join & keep up the journey together. Tag us in photos, and head over to www.whatsawaist.com NOW! Use code (Kylie) for an exclusive discount & I can keep up with your progress!!"

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back at it again

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But, is a waist trainer safe for a woman who just gave birth to use? Turns out, probably not. "A waist trainer is a very tight garment that can be clinched tighter and tighter to pull in the floating rib and anatomically compress," Dr. Cynthia Robbins explained to Us Weekly. "After the delivery of a baby, the body has had ligaments and cartilage softened by a hormone named Relaxin. This hormone has been produced at the end of pregnancy to allow for structure shifting as the baby moves through the birth canal."

She continued: "I advise patients to wear a support wrap or belly wrap postpartum to stabilize the patient’s pelvis so that it is held in place and no longer shifts. This allows for early resumption of exercise and for earlier return to normal function and pre-pregnancy shape. This is a healthy way to quicken recovery."

Kylie gave birth to Stormi back on Feb. 1, and she's gradually made her return to social media after hiding her pregnancy for nine months. She recently has been posting some crazy adorable pics of baby Stormi, as well as some fierce selfies that show off her post-baby body. Maybe the reality star will turn to a more natural way of slimming her waistline after hearing about the negative effects of the waist trainer she's choosing to wear.