It is a necessary biological response for a woman to gain weight during her pregnancy. The weight is added from fat that holds nutrients and water that both provide for and protect the baby. It is not possible to not gain weight during the pregnancy without harming the baby, but there are ways to lose the weight after the birth of the child.
Yes, it is possible, but it is not recommended and it is not healthy to gain that much weight during the first trimester. Most of your pregnancy weight gain should happen during the second trimester.
PREGNANCY
Weight gain is irrelevant during the first trimester. If you had intercourse and missed a period pregnancy is possible.
One can find a pregnancy weight gain chart by visiting the BabyMed website. Other places that one can find a pregnancy weight gain chart are WebMD and Baby Corner.
Usually what stops weight gain in a pregnancy is that your baby is not getting anymore nutrition causing it not to grow anymore.
The amount of weight you gain during pregnancy may depend on the weight you were before pregnancy, it also varies heavily for different people. A woman of average weight should gain approximately 25 - 35 pounds during pregnancy, underweight women often gain 28 - 40 pounds whereas overweight women may gain as little as 15 to 25 pounds.
Depending on ethnicity, heredity and nutrition given during pregnancy, average weight gain should be some where between 10 to 12.5 kg.
No it is not possible to gain weight by just sleeping on your back.
10 lbs
A baby grows inside of you
First signs of pregnancy
I have found an excellent website that will answer all of your "weight-gain-during-pregnancy" questions. The link is: http://www.americanpregnancy.org/pregnancyhealth/eatingfortwo.html It's The American Pregnancy Association's website's section on weight gain during pregnancy, but I think the advice there is good all over the world!!!