Pregnant women, especially those in the third trimester, are at an increased risk of serious complications from the H1N1 A influenza virus, says a new report.

With the H1N1 flu outbreak now elevated to pandemic level, the article in CMAJ (Canadian Medical Association Journal) has reported that oseltamivir (Tamiflu) and zanamivir (Relenza) are relatively safe drugs for use in pregnant and breast-feeding women.

For treatment or prevention during the current pandemic, "oseltamivir appears to be the drug of choice because there are more data on its safety in pregnancy," writes Dr Shinya Ito, Head of the Division of Clinical Pharmacology and Toxicology at SickKids.

Zanamivir can be used, although there is less data available about its safety in pregnant women, the expert added.

Neither drug appears to affect the growth and development of the foetus, although ongoing data collection is important. The groups at high risk of flu-related complications from the novel H1N1 influenza are the same as those for seasonal flu – pregnant women, children under 5 years, the elderly and others such as those with chronic lung conditions.

Only small amounts of oseltamivir and zanamivir are excreted into human milk. If an infant is breastfed by the mother on these drugs and needs treatment, the recommended dose of oseltamivir or zanamivir should be given to the infant.