Getting a flu shot should be an expectant mother's top priority this fall and winter.

Only about half of all pregnant women in the United States get a flu shot each season, leaving thousands of moms-to-be and their babies at increased risk of serious illness.

"Getting a flu shot should be a routine part of prenatal care," said Edward McCabe, March of Dimes chief medical officer. "Health care providers should offer their pregnant patients a flu shot each year and if they don't, then women should ask for it."

Researchers said all pregnant women and those planning to become pregnant should receive a flu shot because the normal changes to a pregnant woman's immune system, heart and lungs put moms-to-be at increased risk of the harmful effects of flu infection. Also, babies born to mothers who got their flu shot while pregnant were protected from serious illness from influenza during their first six months of life. They also had a lower risk of flu-related hospitalizations for chronic asthma, heart conditions, diabetes, a weakened immune system, and other health-related problems.

Previous studies have found that immunized moms did not have a higher risk of babies being born too soon or developing a birth defect when compared with babies born to women who did not get a vaccine. Also, researchers found that women who were vaccinated were less likely to experience a stillbirth.

The Centers for Disease Control and Prevention recommends that everyone six months of age or older, including pregnant women, be vaccinated annually against the influenza virus.

In addition to getting their annual flu shot, pregnant women can lower their risk of catching influenza by limiting contact with others who are sick; coughing or sneezing into a tissue or an arm; not touching the eyes, nose and mouth; washing hands with soap and water before touching others; using hand sanitizers; using hot, soapy water or a dishwasher to wash the dishes and utensils; not sharing the dishes, glasses, utensils or toothbrush.

Those who develop influenza infection symptoms, such as sudden onset fever, muscle aches, and cough should contact their health providers as soon as possible to begin the treatment.