During pregnancy the circulatory system, like the respiratory system, is incredibly efficient, ensuring that both you and your baby receive the extra-oxygenated blood you need. Your lung capacity increases, and you may actually add a few inches to the size of your rib cage. While you may notice that you breathe slightly faster while pregnant, you may not know that you are breathing more efficiently, exhaling and inhaling more air during each breath. At times during your pregnancy you may feel shortness of breath. These feelings of breathlessness do not mean that you or your baby is lacking oxygen. It just means there is less room for your lungs to expand and your body is protesting this aggravation a bit. Most of the time you are not even conscious that you are breathing more deeply, but sometimes you may catch yourself sighing, which is another way, your body helps you take an extra deep breath.