However, vaccine experts believe the findings may be due to older age and other miscarriage risks, not the flu shots.
The study was published in the journal Vaccine after being rejected by two other medical journals. Vaccine Editor-in-Chief Dr. Gregory Poland, who is director of vaccine research at the Mayo Clinic, told the AP he doesn't believe flu shots caused the miscarriages.
There is no reason to change the federal government recommendations that all pregnant women get a flu shot, said health officials, who added that the flu itself is a much greater threat to women and their fetuses.
Two of the study authors were Centers for Disease Control and Prevention researchers. The CDC alerted the American Congress of Obstetricians and Gynecologists about the study so its members could prepare for a potential surge of anxiety among pregnant women, the AP reported.
"I want the CDC and researchers to continue to investigate this," said Dr. Laura Riley, a Boston obstetrician who heads a committee on maternal immunization. "But as an advocate for pregnant women, what I hope doesn't happen is that people panic and stop getting vaccinated," she told the AP.
Some of the study authors are conducting a larger study with more recent data to determine if a possible connection between swine flu vaccine and miscarriage can be confirmed, according to study author James Donahue, of the Marshfield Clinic Research Institute in Minnesota.
He said the earliest that results would be available is next year, the AP reported.
In a statement following publication of the study, the American College of Obstetricians and Gynecologists said: "ACOG continues to recommend that all women receive the influenza vaccine. This is particularly important during pregnancy. Influenza vaccination is an essential element of prenatal care because pregnant women are at an increased risk of serious illness and mortality due to influenza. In addition, maternal vaccination is the most effective strategy to protect newborns because the vaccine is not approved for use in infants younger than six months."