Every girl or woman on planet earth is weight conscious to at least a certain extent. It is almost second nature to them. If she's too thin, then she wants to gain more weight. If she's too overweight, or even a little overweight, she wants to reduce every bit of those last overweight pounds. That's just how women are made.
And when women move towards pregnancy, their greatest fear and challenge is the same: weight gain! And weight gain in reality, for pregnant women, is just that; a challenge. The weight that you gain during your pregnancy is the most important thing. The weight gain can act as a yardstick to measure the success of the pregnancy. What you weighed before the pregnancy, how much you should gain during the pregnancy, what kind of diet you should take during the pregnancy etc are all important elements to consider.
An aptly weighted woman will need to gain around 26 to 28 pounds altogether, if she is expecting only one child. However, if she is expecting twins then she needs to gain 35 to 40 pounds. The required weight gain, which signals a good pregnancy, will increase according to the number of babies that the mother-to-be is expecting at the same time.
The weight that is gained overall is not just that of the baby's. The total baby weight includes several other things that contribute to it, such as the baby's actual weight (8 pounds approx.), the placenta (2 to 3 pounds), the amniotic fluids (2 to 3 pounds), the breast tissue (2 to 3 pounds), the uterus (2 to 5 pounds), fat stores (5 to 9 pounds), and the blood supply (4 pounds). In a nutshell, around 25 pounds of the weight that the mother gains is the "baby weight" i.e. the weight that is essential for the development of the baby.
One of the most important aspects, before you can work up your diet to increase weight, is your actual weight i.e. the weight that you had before the pregnancy. The weight before your pregnancy does effect the baby weight that you must gain during the pregnancy.
If the mother-to-be is underweight, then she must work to gain at least 28 to 40 pounds altogether. And if the mother-to-be is overweight, then she won't need to gain much baby weight; she may need to gain as little as 11 pounds in total during the pregnancy.
The weight that the mother-to-be gains during the pregnancy is directly tied to the total fat stores in the body needed for a proper delivery and breast feeding. This is the reason why so much importance is tied to the weight of the mother-to-be during the pregnancy. If the mother-to-be becomes overweight, it might present complications during the delivery of the baby. In the same way if the mother-to-be is underweight, it may undermine the development and nourishment process of the baby. Therefore, a woman's weight before pregnancy affects the amount of total baby weight that needs to be gained.