Despite landing in the hospital more often if they catch the flu, only about a quarter of pregnant women in the U.S. get vaccinated against it.  Since the U.S. flu season officially begins in October, now is a good time for mothers-to-be to get their flu shot.

The American College of Obstetricians and Gynecology is urging all pregnant women to get the flu shot, and last week the Center for Disease Control and Prevention asked health providers to encourage pregnant women to get flu shots.

While the recommendation itself isn't new, a report published in the journal Obstetrics and Gynecology adds evidence on the safety and effectiveness of the vaccine, and notes that the shot not only protects the woman, but also her baby.

As a Pediatrician, Dr. Sue sees mothers and mothers-to-be on a weekly basis. She says getting the flu shot should be a top priority for expectant mothers.

“I see many expectant mothers who are totally surprised when I ask them if they have received a flu vaccine from their OB. In fact only 1 in 7 pregnant women are being vaccinated. This may be partially due to the fact that OB’s have not routinely been vaccine providers, as we pediatricians have been, and are now becoming more aware about universal recommendations for flu vaccine in pregnancy and are ordering vaccine for their patients to receive during routine obstetrical visits. Flu vaccine is safe throughout pregnancy.”

Dr. Sue also emphasizes the benefits passed along to the newborn.

“As an added benefit of vaccination, the antibodies that a pregnant woman will produce after vaccination will then be transported across the placenta to help protect the newborn. Passive transport of maternal antibodies may be the best protection for a newborn in the first two months of life. This is especially important for those infants being born during the height of the flu season”

While some flu vaccines contain the mercury-based preservative thimerosal, a recent study found the compound did not increase the risk of autism, as some have worried.

While the CDC does not recommend against vaccines containing the preservative, it 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.

n 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.