Unborn children suffer no harm when their mothers take flu medication during pregnancy, a study of some 700,000 women said Wednesday.
It was the largest study ever to assess the potential risks of taking oseltamivir or zanamivir (better known as Tamiflu and Relenza) -- the two main drugs to combat serious flu infections -- during pregnancy, its authors said.
The team compared almost 6,000 pregnant women in Denmark, Norway, Sweden and France who were prescribed oseltamivir or zanamivir between 2008 and 2010, with nearly 700,000 who were not.
Taking into account factors such as age, smoking and the use of other medicines, the team found "no increased risks of adverse outcomes" from one group to the next.
These included low birth weight, preterm birth, stillbirth or birth defects.
On the contrary, the team found that children whose mothers had been prescribed Tamiflu or Relenza, drugs known as neuraminidase inhibitors, were less likely to be underweight.
Influenza flares every winter, putting millions of pregnant women at risk of severe illness during seasons with an aggressive virus strain, the research team said.
Many medicine watchdogs therefore recommended the use of flu drugs, "despite limited knowledge on their safety and effectiveness during pregnancy".
This study, published in The BMJ medical journal, sought to correct that.
The team conceded there were shortcomings in the study, including that they did not assess risks to the child before 22 weeks of pregnancy, and did not know whether women prescribed the drugs had actually taken them.