How to Stay Fit While Pregnant

Why does it seem that stars drop the baby weight so quickly after giving birth? Their secret is that most of them stay fit while expecting. (While putting on 28 to 40 pounds is healthy, many of us admittedly go overboard.) Linda Melone, nutritionist and certified fitness instructor, says women can bounce back to their pre-baby bodies quicker if they follow a simple, low-impact routine that includes yoga, stretching and water workouts. Bonus benefit: Exercising while pregnant can prevent gestational diabetes, alleviate lower-back pain and even lessen the "baby blues," according to The American College of Sports Medicine. Read on for details:

1.    Yoga
Real Housewives of New York's Bethenny Frankel alternated yoga sessions with 45-minute walks three times a week while pregnant with daughter Bryn (born May 8). Just three weeks later, she showed off her size-4 bikini bod in Us Weekly! Melone recommends taking these precautions before launching into downward dog:

•    Abstain from Bikram ("hot" yoga), which raises the body's core temperature above the recommended 102 degrees.
•    Avoid any poses lying on your back after the first trimester or any extreme stretching.
•    Since your center of gravity changes as the baby grows, use caution with balancing moves -- use a wall or other support to avoid falling.
•    Twist from the shoulders vs. the abdomen and only go as far as comfortable.
•    In general, safe moves include the Cobra (first trimester only), side bends, triangle, cat-cow, triangle pose and avoid backbends, hand/headstands, one-legged balance poses without support. MSN: 5 surprising ways yoga affects your health

PHOTOS: Incredible post-baby bodies

2.    Stretching
"Many women experience sciatica [nerve pain] during the third trimester and are unable to do much more than stretch, which helps ease the pain," points out Melone. But, she warns, use caution with extreme stretching because relaxin, a hormone produced during pregnancy, makes muscles more pliable than usual; stretch only within your pre-pregnancy range-of-motion. MSN: How to stay motivated to workout while pregnant!

3.    Water Workouts
Pregnancy often puts pressure on joints and internal organs, but the buoyancy and support of water can provide relief for sciatica. As with all workouts during pregnancy, work within your comfort zone, avoid extremes such as swimming an exorbitant number of laps, stay hydrated and avoid becoming overheated. MSN: 10 things that might surprise you about being pregnant

PHOTOS: The no-gym workout!

4.    Don't Start a New Activity When Pregnant
"If you're a runner, you can keep running if you're comfortable. But you typically don't want to start a running program or jump into a new vigorous activity at this time," says Melone. "The American College of Sports Medicine recommends cardiovascular exercise three to seven days a week for 30 to 40 minutes at a moderate intensity, with no extremes in intensity." Melone also says not to be worried if your stamina decreases. "The amount of exercise a [pregnant] woman can do varies depending on the trimester," she says. While some women find only stretching comfortable, others "continue their pre-pregnancy program up until labor without a hitch." MSN: What to eat post-pregnancy to reclaim your body

VIDEO: How Kendra got her post-baby body back

-- By Jeri Condit, Senior Editor, MSN Health & Fitness, for UsMagazine.com