Causes of Shortness of Breath During Pregnancy
Early in pregnancy, increased levels of the hormone progesterone cause you to breathe more often. This can look and feel like shortness of breath. This hormone expands your lung capacity, allowing your blood to carry large quantities of oxygen to your baby.

Later in pregnancy, shortness of breath occurs as your growing uterus takes up more room in your abdomen. Your uterus pushes on and shifts other organs in your body. Around the 31st to 34th week of pregnancy, the uterus begins to press on the diaphragm (the flat muscle that moves up and down when you breathe). These changes may make it hard for your lungs to fully expand. This may cause more shallow breathing, and you may feel short of breath.

During the last few weeks of pregnancy, this feeling may lessen when your baby settles deeper into the pelvis to prepare for birth. With the baby in this position, some of the pressure on the lungs and diaphragm will decrease.

Shortness of Breath: What You Can Do
These tips may help you to breathe easier: 

• Sit or stand up straight. Sitting up straight will allow your lungs more room to expand.
• Slow down. When you move more slowly, you lessen the work of your heart and lungs.
• Sleep propped up. To put less pressure on your lungs, prop up your upper body with pillows.

When to Talk to Your Health Care Provider
It's normal to feel a mild breathlessness during pregnancy. Talk to your health care provider immediately if your breathlessness becomes severe or comes on very suddenly. Also, call your health care provider right away if you have any of these symptoms:

• A rapid pulse
• Heart palpitations (your heart beats fast and strongly)
• Feeling dizzy or faint
• Chest pain
• Blueness around the lips, fingers or toes
• A cough that doesn't go away
• Coughing up blood
• Fever or chills
• Worsening asthma

Any illness that affects breathing can be more serious during pregnancy. If you have asthma, be sure to talk to your health care provider about how to best manage this condition during pregnancy. Your asthma may stay the same, worsen or improve during pregnancy. Women with moderate to severe asthma are at increased risk of an asthma attack during the third trimester of pregnancy and during labor and delivery.