The number of women giving birth to children at 35 years of age or above is on the rise in Australia, with their percentage increasing from 15 to 21 per cent during the last decade.

A national snapshot of mothers and babies revealed that one fifth of mums giving birth were aged 35 or older and that has risen to over 21 per cent in 2006 from 15 per cent in 1997.

The report also revealed that the average age of first time mothers has been found to be 28 and Caesarean sections made up almost one third of births in Australia.

About 84 per cent of mothers giving birth in 2006 who had previously had a caesarean section had another caesarean section.

Data compiled by the Australian Institute of Health and Welfare in its 16th annual report on pregnancy and childbirth further said there were 9,750 more births in 2006 than in the previous year, the 'Herald Sun' reported.

Of the babies born in 2006, eight per cent were pre-term (less than 37 weeks gestation), compared to seven per cent in 1997.

Six per cent of live births in 2006 were of low birth weight (less than 2500 grams) and 15 per cent were admitted to a special care nursery or neonatal unit.