By Evin Billington

Serena Williams sent the Internet into a frenzy last month after revealing that she was two months pregnant when she won her 23rd grand slam title at the Australian Open in January. Working out with a baby on board might seem potentially dangerous, but doctors say that it’s generally fine for pregnant women to maintain their normal level of activity.

Williams isn’t the only athlete to compete while expecting. Here’s a list of the most amazing sports feats by moms-to-be—proving once and for all that there’s no limit to what pregnant women can achieve.

Dana Vollmer

In April, four-time Olympic gold medalist Vollmer swam the 50-meter freestyle at the Arena Pro Swim Series while she was six months pregnant. The self-dubbed “momma on a mission” wore a green suit (instead of pink) over her bowling ball–size bump during the race as a way to reveal her baby’s gender—a boy!

RELATED: What Pregnancy Does to Your Health

Kerri Walsh Jennings

The beach volleyball champ was 5 weeks pregnant during the 2012 London Olympics, where she scored her third Olympic gold. The most amazing part? Though she knew she felt different going into the competition, Walsh Jennings wasn’t sure she had actually conceived. “When I was throwing my body around fearlessly, and going for gold for our country, I was pregnant,” she told TODAY.

Alysia Montaño

In 2014, the track star ran an 800-meter race at the USA Track & Field Outdoor Championships. Montano was an incredible 34 weeks at that point, and she later said she trained and competed throughout her pregnancy because she felt it was good for her and her baby.

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Catriona Matthew

Scottish golfer Matthew won the 2009 HSBC LPGA Brazil Cup while she was 5 months pregnant with her second child. After the tournament, she told Golf that being an expecting mom didn’t impact her performance. “When you play well you don’t feel tired. Maybe tomorrow I will feel it a bit.”