Despite landing in the hospital more often if they catch the flu, no more than a quarter of pregnant women in the U.S. get vaccinated against it.

That’s according to the American College of Obstetricians and Gynecologists, which has issued a recommendation urging all pregnant women to get the flu shot.

While the recommendation itself isn’t new, the statement, published in the journal Obstetrics and Gynecology, adds evidence on the safety and effectiveness of the vaccine, said Dr. William M. Callaghan of the Centers for Disease Control and Prevention in Atlanta.

He said the CDC and several medical associations back the statement, which notes that the shot not only protects the woman, but also her baby.

Flu vaccines aren’t approved by the Food and Drug Administration for infants younger than six months of age, but babies can get the protective antibodies naturally through breast milk if their mother got the vaccine.

While some flu vaccines contain the mercury-based preservative thimerosal, a study out last week found the compound did not increase the risk of autism, as some have worried. (See Reuters Health story of September 13)

The statement does not recommend against vaccines containing preservative, but notes that thimerosal-free alternatives are available.

It adds that there have been no reports of side effects in pregnant women or their babies, but that women should only get the inactivated vaccine.

Last week, the CDC asked healthcare providers to encourage pregnant women to get flu shots.

This could have a large impact on women’s decision-making, according to data from 2006 and 2007 surveys of pregnant women in Georgia and Rhode Island.

The findings, also published in Obstetrics and Gynecology, show less than one in five women in Georgia had been vaccinated against the seasonal flu. Many of those who hadn’t, said their doctors had never broached the topic.

By contrast, nearly a third of women in Rhode Island had been vaccinated, with encouragement from a healthcare provider increasing the chances more than 50 times.

In its letter to physicians, the CDC said pregnant women were more susceptible to severe illness caused by flu, and accounted for one in 20 deaths from H1N1 influenza (swine flu) in 2009. By comparison, only one in 100 was pregnant in the population.

“We know for certain that there are changes in the immune system that allow the pregnancy to continue,” Callaghan told Reuters Health. “Perhaps the downside is that they also allow the virus to persist.”

The U.S. flu season starts in October and lasts through May.

SOURCE:  Obstetrics and Gynecology, online September 21, 2010.