Water aerobics classes can help pregnant women avoid some common side-effects of heat â?? feeling tired and being less active.

"I have to be healthy. The babies have to be healthy," said Rachel Mulder, who hadn't gone to exercise classes before she conceived twins.

"I don't want to go on bed rest," Mulder explained. "I don't want them to be premature. It was really important to me."

Marybeth Winstead, with Healthy Moms, teaches a toned-down water aerobics at the Golds Gym in North Hills.

"The goal is not to get in any better shape but to continue with the fitness level that they are currently at," Winstead said.

Doing that will help the women have a more successful labor and get their old, slimmer body back quicker.

Taking brisk walks was getting hard for Melanie Seamster, but in the water, walking's a breeze, she said.

"You don't feel the weight of your body, and your joints are much, much better off," Seamster said.

"(It) takes the pressure off my back, and I leave feeling so good," agreed Mulder.

Water resistance helps pregnant women get a thorough workout in a shorter amount of time than they would on land.

"Getting in the water makes mom feel buoyant, ... moms tell us they love the fact that they feel like they don't weigh a thing," Winstead said.

"The number one thing they say," she added, "is they wish they could just stay in the water the whole pregnancy."

If you're pregnant and want to join a water aerobics class, doctors recommend finding an instructor who is trained and certified in pre-natal fitness.