More Australian women are having children later in life, with the number giving birth over 35 almost doubling in the space of two decades.
An Australian Institute of Health and Welfare report notes more than 76,000 babies were born in 2019 to the age group, compared to 69,000 in 2009 and 42,000 in 1999.
"The average age of all women giving birth in Australia has been rising, including for first-time mothers," AIHW spokeswoman Bernice Cropper said.
"The average maternal age has increased from 27.1 years in 1979 to 30.8 years in 2019 for all mothers."
In 2019, more than 60 per cent of women were 30 or over when they gave birth, compared with 54 per cent in 2010.
One quarter of all women giving birth in 2019 were 35 or over. Two in seven of those gave birth for the first time.
The report found mothers over 35 were more likely to live in cities than their younger counterparts, with more than a quarter residing in the highest socioeconomic areas.
Victoria and the ACT had the highest proportion of women 35-plus giving birth (28 per cent), with the Northern Territory (19) and Tasmania (20) the lowest.
"There can be advantages to giving birth later in the life and the majority of older mothers will have uncomplicated pregnancies and healthy babies," Ms Cropper said.
"However, women who give birth later in life are more at risk of complications, such as gestational diabetes (18 per cent of mothers aged 40 and over compared with 10 per cent aged 20-34), during pregnancy and birth.
"Other complications include increased risk of gestational hypertension, pre-term birth and low birthweight babies. This is particularly seen for women giving birth for the first-time."
Mothers aged 40 and over are slightly more likely to have a baby born pre-term or requiring admission to a special care nursery.
The rate of women aged 40-44 giving birth has almost doubled from 8.4 per 1000 women in 1999 to 15.5 per 1000 in 2019.
The rate almost quadrupled among women 45-49 over the same period, from 0.3 per 1000 to 1.1 per 1000.
Australian Associated Press