Part of postpartum recovery is being patient with our midsections. After all, they’ve stretched out to accommodate a growing human, so our abs deserve to be babied a bit. That’s just easier said than done, right? But now the experts say that—while it’s tempting do crunches ASAP—the wrong postpartum ab exercises could do more harm than good.

For many moms, the postpartum tummy isn’t just a little fluffier than the pre-baby version: A third of us have diastasis recti, a separation of the abdominal muscles.

During pregnancy, the muscles move and a gap forms along the center of the abdomen. When the baby comes, the gap doesn’t close instantly. This commonly causes a bit of a tummy pooch as well as lower back pain.

Crunching your core may seem like the solution. But despite what online workout guides suggest, some common exercises will actually make diastasis recti worse.

“You have to be very careful,” personal trainer Leah Keller told NPR this week about her concerns with popular postpartum ab routines floating around the internet. “For example, please don’t ever again in your life do crossover crunches or bicycle crunches. They splay your abs apart in so many ways.”

Although the American College of Obstetricians and Gynecologists recommends abdominal exercises for the perinatal period, it doesn’t give moms any direction on which routines we should be doing after giving birth.

For now, what not to do is a bit clearer—although a small study suggested the Dia Method used by Keller did successfully help 63 mothers heal from diastasis recti in three months by adhering to the daily 10-minute exercise program.

That sounds like a promising option (for a small price), but there are alternatives: For one, talk to your healthcare provider after your baby comes and let her know if you plan to exercise with a focus on your abs. She may be able to recommend a physical therapist, personal trainer or simply a few exercise moves she feels are safe for you. There are also workout classes specializing in diastasis recti repair popping up around the country, which a lot of moms have anecdotally found to be helpful.

Whatever you do, be kind to your body. Pregnancy changes a body in a lot of ways, and it’s unrealistic to expect that “mommy tummy” to be flat before your baby is even sleeping through the night.

This post was originally published on August 8, 2017. It has been updated.