Pregnant women in Norway who got vaccinated against the swine flu virus that caused the 2009-2010 pandemic showed no increased risk of pregnancy loss, contrary to popular belief, says a study released Thursday.

Pregnant women who came down with the flu did however have increased risk of miscarriage and still birth, said the study carried out in Norway.

Scientists at the US National Institutes of Health and the Norwegian Institute of Public Health published their findings online in the New England Journal of Medicine.

During the H1N1 flu pandemic, Norway urged pregnant women to get vaccinated. But some expectant mothers shied from this after news reports of pregnancy losses after flu shots.

The researchers said their study suggested that influenza infection may increase the risk of fetal loss.

They reached their conclusion by analyzing Norway's well-kept archives of registries and medical records.

The risk of pregnancy loss can be multiplied by a factor of two if a pregnant woman catches the flu, while vaccination reduced this risk.

"Most important is that vaccinations protect pregnant women against influenza illness, which could be harmful for both the mother and the baby," said Allen Wilcox of the NIH, co-author of the study.