Surfer Bethany Hamilton is hanging 10 at 26 weeks. The one-armed wave runner, who is six months pregnant, is defending her right to ride with a protruding belly. "Giving birth may be one of the most physical events a woman goes through, so being active and keeping muscles alive and ready is what I believe we need to do," she toldFitBump360.com. But Hamilton, who lost her left arm in a 2003 shark attack and had her story turned into a movie, should pick a different workout while she’s expecting. "Surfers have a chance of falling in the water, and hitting big waves can cause trauma to the abdomen," says Dr. Daniel Roshan, an ob-gyn with NYU Langone Medical Center. Moms-to-be can still exercise — even up until delivery — but should keep things light, he said. The American Congress of Obstetricians and Gynecologists agrees, ruling that pregnant women should avoid "activities with a high risk of falling or those with a high risk of abdominal trauma." They're cautious for good reason: Excessive prenatal exercise can have devastating consequences, like bleeding, premature labor, ruptured membranes, and problems with the placenta and cervix. PreviousNext EnlargeBETHANY HAMILTON VIA YOUTUBE Bethany Hamilton and Adam Dirks announced they are expecting on Feb. 8. Hamilton did say she modified her usually intense moves — beach sprints, explosive squats, stair-climbing — when she got pregnant. But she's still on the spin bike, and gets counsel from a holistic health pro. And the surfer — who announced her pregnancy in a video last month with husband Adam Dirks — says she has every intention to stay up on the board "as long as I can." "Once the belly's pretty big, maybe (I'll) just mellow it out and spend more time swimming and enjoying the ocean," she added. Preferably not too much time though: Pregnant women should only work out for 30 minutes a day, Roshan said. "You don't want to exhaust yourself (so) more blood will go to the baby," Roshan said. She's not the only one making waves for her pregnancy habits. Last week, model Sarah Stage came under fire for flaunting her baby belly, hidden behind some serious six-pack abs.