Pro-surfer Bethany Hamilton went skateboarding at 9 months pregnant and people are concerned

Pro-surfer Bethany Hamilton, who gained international fame at age 13 after a shark attack caused the loss of her arm, just celebrated her birthday while nine months pregnant with her second child. She marked the occasion by going skateboarding.

In an Instagram video, Hamilton can be seen effortlessly carving up a road on her skateboard with her baby bump on full display. “My birthday skate session! Cement waves,” she wrote in the caption. While plenty of people remarked in the comments at how impressive it was — and how amazing she looked doing it — others pointed out that skateboarding isn’t really recommended when you’re pregnant.

“You’re not supposed to do that when you’re pregnant,” one person wrote. “I know you are an expert but … this still scared me a little,” another said. “Be careful girl, baby on board,” another chimed in.

Pregnant women who are healthy are generally advised to get 150 minutes of exercise a week by the American College of Obstetricians and Gynecologists, the ruling body for ob-gyns. But not all exercise is created equal.

ACOG specifically lists out exercises that are considered safe, including walking, swimming, stationary biking, yoga, and racquet sports. It’s also safe to run, jog, or do strength training if you regularly did it before you became pregnant, the organization says.

But there are plenty of exercises that fall under ACOG’s list of activities to avoid, including contact sports, scuba diving, hot yoga and Pilates, and exercises “with a high risk of falling” like surfing, skiing, gymnastics, and horseback riding.

Hamilton is likely aware of the surfing warning. She said in a December Instagram post that she hasn’t been surfing, which she called the “hardest” part of her pregnancy. “I’m taking a lil break, but it’s soooo worth it!” she wrote. “Grow baby grow.”

ACOG doesn’t specifically call out skateboarding, but it definitely falls under the category of exercises to avoid, women’s health expert Jennifer Wider, MD, tells Yahoo Lifestyle. “The walls of the uterus are strong, thick muscles, designed to keep a growing baby safe,” she explains. “But if you have a hard enough fall, one worry is that the fall can put you into labor, or trigger an early delivery, especially if you fall in the third trimester.”

The simple act of falling can also injure you and your baby, Christine Greves, MD, a board-certified ob-gyn at the Winnie Palmer Hospital for Women and Babies, tells Yahoo Lifestyle. Your placenta, which supplies oxygen and nutrients to the baby, is also at risk of being injured in a fall in something known as placental abruption, Greves says. And if the placenta is harmed, it can deprive the baby of oxygen and cause a life-threatening situation, she says.

Unfortunately, the risk of falling exists, even if you’re an expert skateboarder like Hamilton. When you’re pregnant, your stability and balance is thrown off, making it more likely that you’ll fall in situations where you wouldn’t otherwise, Greves says.

While it seems like Hamilton made it through her skate session safely (and she clearly had a blast doing it), Wider says it’s really best to avoid this kind of exercise until after you give birth. “Take a pass,” she says. “Regardless of your athletic ability, pregnancy is not the time to engage in any high-risk or extreme sports.”

Read more from Yahoo Lifestyle:

• What 11 Olympians do in the morning to start their days off right

• How I lost 150 pounds: ‘My dream of becoming a mother kept me motivated’

• Why 20-year-old Kylie Jenner’s pregnancy is beautiful—but an exception

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