We've heard the story a million times: A woman is going through pregnancy complications—especially if she's having twins—and the doctor prescribes bed rest. When you're retaining water, having hot flashes and are breathing so heavily that you could be mistaken for a crank caller, it sounds like a dream come true. It's basically doctor-imposed relaxation. Cue the dream sequence of you at the spa for weeks on end. Not bad, right?

Reese Witherspoon was placed on bed rest with her third child, Tennessee; Marcia Cross missed the Golden Globes because of it when she was pregnant with her twins, Eden, and Savannah; Pilates devotee Julia Roberts had to give up her fitness classes in favor of bedside games of Scrabble with hubby Danny Moder when she was pregnant with twins Phinneaus and Hazel.

Singer and American Idol judge Mariah Carey had a super-complicated pregnancy with twins Monroe and Morocco—she developed gestational diabetes, then oedema, which is when fluid develops under your skin. It usually only happens in women's feet and ankles, but Mariah's condition started to spread up her body. All of that combined lead to several false labors and emergency trips to the hospital that she was finally placed on bed rest. "I had a really tough pregnancy," Mariah told Barbara Walters on 20/20. "It was so bad that even the bed [rest] hurt."

After years of it being the go-to answer for women with difficult pregnancies, a new study suggests that bed rest might be causing more harm than good. In a study conducted by the National Institutes of Health, 40 percent of women who cut out activity had a premature baby, compared to 17 percent of women who didn't scale back. Researchers say bed rest also increases the risk of blood clots, and bone and muscle loss.

While one study doesn't prove absolutely conclusive, its findings do warrant a discussion with your doctor, if your physician suggests bed rest. At the end of the day, it's important for you to trust your doctor's expertise (all of those years of schooling and training mean something!), but you need to feel good about your decision as well. So it's best to be as knowledgeable about the situation as you possibly can be. Don't be afraid to ask questions!

Tell us: Have you ever been placed on bed rest? Do you think it was the right decision?