Should a pregnant woman at high risk for obesity engage in a diet and exercice???

Yes. However, being pregnant changes the kinds and intensities of exercises. No bouncing, ab crunches, or sit ups because that stresses the ab muscles. Pregnancy loosens tendon and muscle tissues, and if you put too much stress on your abs during prenancy, you can cause damage.

Better exercises are gentle stretching, walking, swimming, stationary biking (as long as you can), stair stepping.

As for diet, 2000 calories/day was what my oby/gyn prescribed for me when I had gestational diabetes. You should consult with a nutritional specialist so you avoid extra weight gain and possible complications. Your non-pregnant body doesn't need junk food and neither does your baby now you're pregnant! Switch to drinking only water; you'll be amazed how many calories that cuts out.

Remember, it's easy to start exercising. Just put on your walking shoes and start down the block. Listen to some good music through your iPod or CD player as you go. Find a walking buddy. Take along a bottle of water to keep hydrated. Just make sure you don't make refreshment stops
at fast food restaurants along your route! Source(s): experience

Yes, if it is done with a physician's close guidance.
CONSULT THE OBGYN BEFORE DOING ANYTHING.
yes you should start exersing while pregnant but nothing strenuous...maybe climb stairs and walk and stuff but dont diet...rather just eat healthy...such steps will help you lose the baby weight much faster
A must: Consult a doctor, and take no other advice than that from this post.
Why not? If you're having a normal pregnancy and are basically healthy, there's no reason to change your usual routine if you exercise, etc.. I worked full time in a very busy ICU until 5 days before my first baby was born and did just fine. As for dieting, ask your doctor for some guidelines. You'll need to be sure you're getting enough calories and enough of the essential vitamins and minerals.
your OB needs to answer this question.