May Li Lim and colleagues studied 211 women with swab-confirmed influenza H1N1 (2009) infection who had been admitted to hospital in Singapore between May and September 2009.

Nine of the women developed pregnancy complications and there were two cases of pneumonia, although all patients recovered.

The researchers said ‘due consideration should be given to the potential benefit of early diagnosis and treatment'.

Dr Maureen Baker, RCGP pandemic flu lead said evidence from the UK had suggested that early intervention and treatment reduces the risk of complications.

‘Of those people who have been admitted to intensive care or died, many have presented relatively late,' she said. ‘Early treatment in pregnant women seems to matter as much as in other patients, if not more.'

Around 20% of the 16- to 45-year-old women admitted to hospital with flu have been pregnant, the RCGP has said.

The college has said it is ‘vital' that GPs encourage immunisation among pregnant women and other vulnerable groups.

The researchers found a range of common symptoms among the pregnant women in the study. These included runny nose, sore throat and muscle ache, as well as headache and breathlessness.

Around 13% of the women admitted had asthma, compared with 0.5% with hypertension and 1.9% with gestational diabetes.

• BJOG Online 2010