You may feel even more short of breath in the 3rd trimester. Why? As your baby grows larger and takes up more and more of the space inside your abdomen, other organs are squeezed and pushed aside. Your lungs don't have the room they need to expand with a full breath. Your diaphragm can't offer much help because it is compressed too. (This doesn't cause any permanent damage; after your baby is born, your organs will slip right back into their prepregnancy position.)
Don't worry. As always, Mother Nature has provided for your baby. Although you may feel as if you're getting less air, high levels of progesterone help you take deeper breaths and get more oxygen into your blood. And because your blood volume is higher during pregnancy, more oxygen passes back and forth across the placenta as you inhale and exhale.
Easing symptoms. If you become winded during the day, slow down for a few minutes. Your breath should return. Make an effort to sit up straight during the day to give your lungs more breathing room. You can also consciously breathe in a way that raises your rib cage; check that your ribs push out against your hands as you inhale deeply. At night you may feel as if you're hyperventilating. You can ease that sensation by sleeping with your head raised on more than one pillow. If your breathlessness is accompanied by chest pains, call your doctor right away.
Luckily most women get relief from this breathlessness before childbirth. When your baby's head drops into your birth canal -- about 2 or 3 weeks before delivery -- you'll have more room for your diaphragm and breathe more easily.
Asthma sufferers. Women with asthma sometimes find that their symptoms worsen during the 3rd trimester. If your asthma gets worse, talk with your doctor. Many asthma medicines are considered safe during pregnancy. Doctors usually prefer to prescribe inhaled medications because they have a more localized effect and work well; if you discover that your chest feels tight, however, tell your doctor.