There are enough anti-viral drugs stored away in the UK to treat half of all pregnant women in the event of a flu pandemic, according to the government.
The Department of Health has stockpiled 350,000 treatment courses of Relenza to deal with a "reasonable worst-case scenario", which would see 50% of expectant mothers becoming ill. There are around 635,000 births in the UK every year.
Health secretary, Alan Johnson, announced plans last year to double the stockpile of another anti-viral, Tamiflu, so that 50% of the entire population could be covered in the event of a pandemic.
However, Tamiflu is not suitable for pregnant women because it can easily pass across the placenta to the developing foetus.
Relenza is inhaled, which means less of it passes to the baby and it is therefore safe to use, a Department of Health spokeswoman said.
Dr Lindsey Davies, the government's national director of pandemic influenza preparedness, said: "Our preparations for a pandemic are on course and the UK is already one of the best-prepared countries in the world.
"This guidance brings together all the information doctors, midwives and planners need to help pregnant women in a pandemic."
"I think it is best to avoid all medicines – oral, injected, inhaled, ingested – during the early months of pregnancy, unless during an outbreak of a contagious disease or epidemic, to be completely assured that the substance given has had no association with a later illness/condition." - V Henry