A large study led by researchers at Karolinska Institutet, published in the journal The BMJ, finds no increased risks to newborn babies associated with taking influenza drugs known as neuraminidase inhibitors during pregnancy.

Regulatory agencies in Europe and the USA recommend neuraminidase inhibitors for pregnant women to prevent and treat influenza, despite limited knowledge on their safety and effectiveness during pregnancy.

The study, led by Sophie Graner at the Centre for Pharmacoepidemiology at the Department of Medicine, Karolinska Institutet, involved almost 6,000 women in Scandinavia and France who were prescribed any of the two neuraminidase inhibitors, oseltamivir (Tamiflu) or zanamivir (Relenza), during pregnancy – and almost 700,000 who did not receive prescriptions over the same period (2008 to 2010). This is the largest study to date to assess potential risks of taking antiviral drugs during pregnancy.

After several health–related factors were taken into account, such as age, smoking and use of other medications, the team found no increased risks of adverse outcomes including low birth weight, low Apgar score (a test of a baby’s condition at birth), preterm birth, stillbirth, or birth defects.

The researchers say their results “support previously reported findings that the use of neuraminidase inhibitors is not associated with increased risks of adverse fetal or neonatal outcomes.”

The study was funded by Karolinska Institutet in Sweden, Université Toulouse III in France, Norwegian Institute of Public Health and University of Bergen in Norway, Statens Serum Institut in Denmark, the Novo Nordisk Foundation and the Danish Medical Research Council.