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Getting the flu vaccine while pregnant does not increase the odds that the foetus will die in the womb, according to a Norwegian study that looked at tens of thousands of women.
"Vaccination itself was not associated with increased fetal mortality and may have reduced the risk of influenza-related death during the pandemic" of 2009, said a team led by Siri Habert of the Norwegian Institute of Public Health in Oslo.
Although fetal deaths were rare during the study, they were more common in pregnant women with the flu, and other medical experts said it was already known that influenza can be unusually dangerous in pregnant women.
"The increased hospitalization rate is about fourfold higher among pregnant women compared to women of a similar age who are not pregnant," said Jon Abramson of the Wake Forest Baptist Medical Center in North Carolina, who was not part of the study.
The study, which appears in the New England Journal of medicine, encompassed the H1N1 pandemic in the fall and early winter of 2009, and took place after publicity about more than 30 cases of fetal death following vaccination.
Up until then, pregnant women in Norway were not routinely advised to get the flu vaccine. During the pandemic, as much as 30 per cent of the Norwegian population fell ill with the flu.
The vaccine was offered beginning on Oct 19, 2009 and was usually given during the second and third trimester. It wasn't foolproof, but it did cut a woman's risk of developing influenza by 70 per cent.
Among nearly 26,000 women vaccinated during pregnancy, there were 78 fetal deaths, or three per 1,000 pregnancies. Among about 87,000 pregnant women who were not vaccinated, there were 414 fetal deaths, or close to five per 1,000 pregnancies.
When the researchers focused on the women who developed the flu, the risk of losing their child to miscarriage or stillbirth was almost double that of those who had not been vaccinated.
Among all women, vaccination during the study period reduced the likelihood of fetal death by 12 per cent, but that difference could be due to chance, the researchers said.
The researchers also found no evidence that vaccination increased the risk of premature delivery or having a baby with a low birth weight.
"We found no evidence that influenza vaccination of pregnant women increased the risk of fetal death," the researchers said."However, influenza infection itself posed a major risk; among pregnant women who received a clinical diagnosis of influenza, the risk of fetal death nearly doubled."
As a result of mounting evidence of the impact of influenza on pregnant women, the World Health Organisation in the last year actually recommended that a top priority for getting the flu vaccine is pregnant women.