Pregnant women should get the flu shot, regardless of how far along they are in their pregnancies, according to updated guidelines released by the American College of Obstetricians and Gynecologists (ACOG).

The new guidelines by ACOG also state that vaccination is important for women who are trying to become pregnant. Preventing the flu is an essential element of care during preconception, as well as during pregnancy and after delivery, according to a statement from ACOG. [11 Big Fat Pregnancy Myths]

"The flu virus is highly infectious and can be particularly dangerous to pregnant women, as it can cause pneumonia, premature labor and other complications," said Dr. Laura Riley, chair of ACOG's Immunization Expert Work Group, which developed the new guidelines.

Since the last time ACOG issued guidelines on the flu vaccine, in 2010, even more evidence has shown that the vaccine is safe for pregnant women, according to the new guidelines.

"New data show the continued critical need for influenza vaccination during pregnancy," and for providers to recommend and provide vaccinations," the new guidelines say.

Why are pregnant women particularly vulnerable to flu-related complications? During pregnancy, a woman's immune system changes, which results in increased opportunities for seasonal flu viruses to cause complications and serious illness, according to ACOG.

Getting the flu shot when pregnant protects not only expectant mothers, but also babies, who can't be vaccinated against influenza until they're at least 6 months old. The babies of vaccinated women receive antibodies from their mothers while in the womb, helping to protect them against the flu until they're old enough to be vaccinated themselves, according to ACOG.

Since 2009, influenza immunization rates for pregnant women increased each year, but experts at ACOG think more work needs to be done to encourage all pregnant women to get the flu vaccine.

For instance, some people may think pregnant women shouldn't be vaccinated against influenza, but this is a myth, according to ACOG and the Centers for Disease Control and Prevention. The CDC recommends that everyone age 6 months and older, including pregnant women, receive a flu shot every year.

Prior to 2009's H1N1 pandemic, immunization rates for pregnant women were at only 15 percent, ACOG reports. But the rate increased to 50 percent during the pandemic, and this level has been sustained or slightly increased every year since then. ACOG's goal is to increase immunization rates for pregnant women in the United States well beyond the 50 percent mark.

These shots, which do not contain any live viruses, can be administered during any stage of pregnancy, ACOG said.

"Vaccination every year, early in the season and regardless of the state of pregnancy, is the best line of defense," Riley said in a statement.

In the United States, flu season typically starts in October and lasts through May. Women who are breastfeeding or who have recently given birth should also get vaccinated early in the season, according to the new guidelines.

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