Many mothers-to-be expressed concern if the vaccination would affect the baby, so researchers analyzed data from the flu seasons of 2009-12 involving about 1,100 mothers.
Researchers from the University of California, San Diego School of Medicine and Boston University, in collaboration with the American Academy of Allergy Asthma and Immunology found evidence of the H1N1 influenza vaccine's safety during pregnancy.
The national study, which began shortly after the H1N1 influenza outbreak of 2009, found women who were vaccinated were no more likely to have a miscarriage and no more likely to have a baby with a birth defect than women who were not vaccinated.
Christina Chambers of the University of California, San Diego, said unvaccinated pregnant women were more likely to have more complications of influenza if they got sick, more likely to be hospitalized and even to die.
"The overall results of the study were quite reassuring about the safety of the flu vaccine formulations that contained the pandemic H1N1 strain," Chambers said in a statement. "We believe our study's results can help women and their doctors become better informed about the benefits and risks of flu vaccination during pregnancy."
The team from Boston University's Slone Epidemiology Center interviewed 4,191 mothers from four U.S. regional centers in the United States, who had either delivered a baby with one of 41 specific birth defects or delivered a normal infant.
They compared the use of influenza vaccine in the two groups during the 2009-2011 flu seasons. The team also compared the risk of preterm delivery in vaccinated versus unvaccinated women.
The study, published in the journal Vaccine, found overall, no significant evidence of an increased risk of any specific birth defects was noted.