Hemoglobin is very important during times of pregnancy for women. Since you are taking food for you as well as your baby, you should be very careful while doing that. Iron like proteins and carbohydrates are very important for your body. A normal human being needs around 15 mg of iron per day but if you are pregnant, you should take 30-40 mg of iron.
Normally, all women have deficiency of iron in their body. But this deficiency becomes prolonged during times of pregnancy. During the growth of the fetus, the child will take the strength only from iron. It cannot take nutrients from any other elements than iron.
You can intake iron in two ways. The first one is called heme iron which is taken from meat sources and the non-heme iron which is taken from non-meat sources. The iron which is taken from meat is more readily absorbed.