Gaining adequate weight during pregnancy is a sign that you are eating enough food for the baby. Depending on your weight before getting pregnant, the normal weight gain should be between 11 to 15 kg.
During the first trimester, when "morning sickness" is at its peak, it is normal to gain only one to two kg (or sometimes lose weight). At this time, the fetus is so small that it does not require much nutrition. So once you start taking prenatal vitamins, all the requirements of the fetus are met with it. After the first trimester, the weight gain is about 500 grams every week. If your appetite has not increased even in the second trimester or if you are not gaining the expected weight in the third trimester, consult your doctor for a pregnancy diet chart. The good news is that most women solve this problem in some way.
This article explains the causes and remedies for loss of appetite during pregnancy that will surely help you in this situation -
(Read more - Every Mother Should Know : Pregnancy Problems)