Gaining weight is a part of pregnancy and one really cannot and should not try to avoid this. One should realize that during pregnancy, there is another life inside oneself and also a lot of other related stuff such as the birth sac, amniotic fluid, Placenta which add to the weight of the growing foetus as the pregnancy advances. Eat a healthy and balanced diet during the months of pregnancy is extremely important for both mother and child. Without healthy nutrition, proper growth and development of the foetus cannot be assured. A diet for a pregnant woman should have adequate amount of carbohydrate for energy, high protein content, Calcium, all necessary vitamins and minerals, and Iron. Some Iron and vitamin supplements are given to all pregnant woman by doctors throughout the months of pregnancy. However, over eating should be avoided at all times. Over eating will give rise to excessive weight gain which will be eventually detrimental for the mother's health. Recommendation is to keep the calories within 2200 to 2500 Kcal per day. One should also keep in mind that the requirements for first trimester are lesser than that of the advanced months.
Do NOT eat double the amount you normally would. You only need to consume about 300 extra calories per day. Talk to you doctor about how many calories you should be eating. Never diet or try to lose weight while you're pregnant. You are going to gain weight. It's OK. How much you should gain depends on what your weight is now. The more under-weight you are, the more you should gain, and if you are obese you shouldn't gain much at all.
Probably double the same amount you normally eat
You gain weight no matter what if you love your child you wouldnt be so worried about the weight you again but just about being healthly for your child; don't worry so much it all comes back off any way