The first thing you must understand is that pregnancy is not the time to be counting calories. If you are on a diet that involves severely restricting your caloric intake get off it. Right now. For the next nine months you have permission to not suffer for beauty. Not only is restricting calories not going to result in weight loss (youre going to gain some as the baby grows whether you like it or not) it could potentially harm your baby.
Not getting enough calories during pregnancy can lead to the baby not having what it needs to develop properly. Low birth weight is a common complication, as is poor fetal development. The baby may have any number of deficiency-associated birth defects. In short, it is vitally important that when you are pregnant you get enough to eat. You can burn it all off after the baby is born, although to be honest if you have time to worry about your weight you will be handling new motherhood much better than most!
The first thing you want to do is calculate your pre-pregnancy Recommended Daily Caloric Intake. If you are a health buff or have been living on a terminal diet you may already know this number. If you do not you can visit one of the following sites to figure it out, or consult with your physician.
For the first three months of your pregnancy you actually do not need to consume any extra calories. Your pre-pregnancy calorie consumption will be perfectly adequate for your babys growth and development as long as you are not dieting. If you are dieting, stop! This is the number of calories (roughly) that you want to eat in a day.
As you go into your second and third trimester you should increase your daily caloric intake by 300 calories. This will help to compensate for the increasing rate of your babys growth. If your pre-pregnancy caloric intake was 1800 calories you should consume 2100 calories a day. If it was 1400 calories you should consume 1700 calories, and so on and so forth. Again, this is not the time to try and lose weight. Do not omit these extra calories in favor of allowing your body to burn them instead. This is not healthy for you or your baby, and if you are breastfeeding you will quickly work these calories back off.
The number of calories you need during pregnancy is going to vary if you were not a healthy weight when you became pregnant. Women who were obese may be told to consume fewer calories to prevent excessive weight gain, which would place extra strain on the heart and lungs and increase the likelihood of blood pressure related problems during pregnancy. In this case this is a fine time to diet, as long as you are following your doctors advice. The healthier you are, the healthier your baby is going to be.
On the flip side of that coin, if you were underweight at the beginning of your pregnancy or have not gained what the doctor considers to be an adequate amount of weight since becoming pregnant you may be told to increase your caloric intake by more than 300. The baby needs to be able to take enough calories away from your body to grow, and if you dont have any to spare either because you arent eating enough or your body is burning everything that you eat they are going to suffer.