Other studies have found flu vaccines are safe during pregnancy.
Marshfield researchers conducted a similar study among pregnant women during the 2005-2006 and 2006-2007 flu seasons, and found no association between the flu vaccine and miscarriage. Only four of the comparable 485 healthy pregnancies had involved women that were vaccinated in that manner. Health officials say there is no reason to change the government recommendation that all pregnant women be vaccinated against the flu.
It's the first study to identify a potential link between miscarriage and the flu vaccine and the first to assess the effect of repeat influenza vaccination and risk of miscarriage. In the group of women who miscarried, there was a small but significant number who received vaccines to protect against the H1N1 flu virus strain two years in a row, including one shot within 28 days prior to their miscarriages; this link was only apparent in the women who got the vaccinations in consecutive seasons.
The first group contained more women that were at higher risk of suffering a miscarriage such as older mothers, smokers, and those that had diabetes.
That's why doctors are urging people to get vaccinated before the peak of the season. Miscarriages, which are among the most challenging birth outcomes to study, often occur early in pregnancy and don't necessarily come to the attention of health-care providers - or the women themselves if they miscarry before they realize they are pregnant. The researchers tried to make statistical adjustments to level out some of those differences but some researchers don't think they completely succeeded.
The authors said as well that they could not rule out a possible exposure to the swine flu itself that was a factor in prompting some of the miscarriages.
Two other medical journals rejected the article before a third, Vaccine, accepted it. Dr. Gregory Poland, Vaccine's editor-in-chief, said it was a well-designed study that raised a question that shouldn't be ignored.
Now is the time to get your flu shot. "Not at all", said Poland, who also is director of vaccine research at the Mayo Clinic. The results aren't expected until next year at the earliest, he said.