Tory Shepherd has been told countless times that she will change her mind when it comes to parenthood.

Key points: Writer Tory Shepherd is releasing a book on opting out of motherhood

Writer Tory Shepherd is releasing a book on opting out of motherhood She says Australian women are having less children, often by choice

She says Australian women are having less children, often by choice Social media is playing a role in the pressure on women

The Adelaide journalist — and author of On Freedom, a book about how the freedom to choose to have children is reshaping society — said it was a common comment to receive when queried about her motherhood status.

"This is what people say to me all the time," she told ABC News Breakfast.

"People who don't know me — Uber drivers, I don't know why."

She said people would ask whether she had children, and when she said "no" she would be met with "you will change your mind" and "you will get there eventually".

"The subtext is I am incomplete as a woman and I am missing something," she said.

"You have heard the horrible words for women who are without kids — 'deliberately barren' were used about the former prime minister, Julia Gillard.

"Even from strangers you get the sense you have made the wrong choice."

Women are having fewer children

Despite the constant commentary, she is not alone.

Tory Shepherd is the state editor for The Advertiser. ( MUP/News Corp )

According to 2017 figures from the Australian Bureau of Statistics, women are on average having 1.74 children, the lowest rate since 2001.

In 2002, then treasurer Peter Costello asked Australians to have one child for Mum, one for Dad and one for the country.

Shepherd said attitudes had changed since then.

"I don't think these days having a treasurer calling on women to 'have one for the country' would go down as well," Shepherd said.

"It seems a comment right out of time now, although it was just yesterday."

So why is there still pressure?

Shepherd said while times were changing, with couples without children set to outnumber those who have them in the coming decades, social media played a big role in adding pressure on women.

"I haven't known a time when motherhood has been such an aspirational marker, nor such a competitive sport," she said.

"The deification of motherhood is something beyond my thinking.

"What has happened? What got us here?

"Well, actually, there is one interesting theory, which is that we used to have kids and they would bring us money — send them up a chimney or out in a field or whatever, so they were giving us an income.

"Now we spend all of our income on them — they become a precious asset rather than something sent out to work.

"I hate to blame social media for everything, but let's blame social media."

She said there was a "clamour" to be a parent and be glamorous.

"You have people dressing up their kids in extraordinary designer outfits," Shepherd said.

"I didn't get a proper haircut until I was 14 — it used to be the bowl over the head and fringe around the edge — now we give our kids everything we have ourself."

Shepherd is launching her book On Freedom this week alongside SA Commissioner for Equal Opportunity Niki Vincent in Adelaide.