The former model, who represented Australia at the 1997 Miss Universe pageant, discovered she was pregnant after she split with the baby's father and is expected to give birth around her 40th birthday.

She is now 19-weeks "along" and her due date is three days after her November 9 birthday.

"I certainly wanted to tell people I was pregnant and not hide under big jumpers and since I have it's been so nice with loads of support. Now that my friends and acquaintances now know I hope they understand why I haven't been coming out to party as much," she said after making the official announcement, via a photo shoot with her growing baby bump, in the new issue of Woman's Day.

"I didn't know how it would go down, I was terrified but it's certainly been received really well. I will be a single mum and there's a lot of single mums saying, 'I went through it and these are the things you might find difficult or not', so that's really fabulous as well.

"It's exciting. It was unexpected but I'm very happy about it. I've always wanted to be a mum and the fact that I'm able to have a child is a miracle. I've travelled the world and had an amazing career so far and there was never going to be the right time, but now here we are and I'm rolling with it," the Sydney-based socialite told Fairfax Media.

Her former partner, who Csortan will not name, is aware of the pregnancy but will not be involved.

"He respects my decision," she said.

While it hasn't been confirmed she believes she is expecting a girl.

"When the baby's older I'm happy with her finding out who her father is. I'm going into this with an open mind," she said.

The 39-year-old former Getaway presenter is struggling with morning sickness but is, so far, enjoying being pregnant.

"I'm watching my belly get bigger, my bum get bigger and my boobs get bigger, and I'm just embracing it. I have never felt so womanly," she said.

Last year she was reportedly dating Port Adelaide player Chad Cornes after a brief romance with American Abercrombie & Fitch model Josh Slack, who was 11 years her junior.

She and her long-term partner, Silverchair bass player Chris Joannou, separated in 2013 after four years together.

Csortan is now preparing for her off-road bike documentary, which she filmed in Morocco for the National Geographic Channel, to go to air. Riding Morocco: Chasing the Dakar will premiere on Friday and be broadcast to more than 170 countries.

The novice dirt bike rider shot the physically demanding series during the "very early" stages of her pregnancy with co-host Christophe Barrierre-Varju.

"I had no idea and I look back at the vision now and I cringe, oh my god, this poor baby. But it was well protected and nothing's wrong, it might come out a motorbike enthusiast but let's hope not," she said.