Asthma is one of the most common chronic medical conditions, affecting about 6.4 percent of people in the U.S. and 4 to 8 percent of pregnant women. For about a third of these women, the condition -- which causes the airways to narrow and restrict the flow of air -- can worsen during pregnancy; for another third, it may improve; and for the remaining third, it stays the same.

A recent study funded by the National Institutes of Health underscores the need to take care of asthma during pregnancy: Experts found that if the condition isn't treated, it can cause risks to the fetus (such as preterm labor and low birth weight) and increase the risk of pregnancy-induced hypertension. With treatment, however, the condition shouldn't harm a pregnancy, says Carl Della Badia, assistant professor of obstetrics and gynecology at Drexel University College of Medicine, in Philadelphia. He offers the following advice for coping with asthma during pregnancy:

• Causes Factors such as pet dander, dust, pollen, cigarette smoke, viral infections, and heavy exercise can trigger asthma.

• Symptoms Asthma sufferers usually have a cough, wheezing, difficulty breathing, or a tightness in the chest. These symptoms may be more pronounced early in the morning and late in the evening.

• Diagnosis First, your doctor will listen to wheezing and whistling sounds as you breathe out. (Asthma is more severe if these sounds are made when you also breathe in.) This is usually followed by a discussion about your environment to identify potential asthma triggers.

• Treatment Most medications are safe to use while you're pregnant. A bronchodialator, an inhaled medication that relaxes and opens up the airways, is the first line of treatment. If symptoms don't improve, anti-inflammatory medications (such as inhaled corticosteroids) may be given to reduce the inflammation that causes the airways to narrow. "These medications are safe for use during pregnancy because they only go into the lungs and are not absorbed by the rest of the body," says Herbert Patrick, M.D., associate professor of pulmonary and critical care medicine, also at Drexel. In severe cases, stronger medication, taken orally, may be recommended, says Dr. Patrick. For information about asthma medications during pregnancy, contact the Asthma Medication and Pregnancy Project at 888-523-4847. Your doctor will also likely recommend that you bring your inhaler to the hospital when you deliver, in case you have an asthma attack during labor.

• Prevention Identifying and removing asthma triggers from your environment is the best prevention. Keep smokers and pets at a distance, and have your home dusted and cleaned regularly. (Air purifiers can help get rid of dust.) For more information, visit the American Academy of Allergy, Asthma, & Immunology website at www.aaaai.org or the American College of Allergy, Asthma, & Immunology at www.allergy.mcg.edu.

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