Michelle Bridges announced she was pregnant on Thursday. The 44-year-old also confirmed that the conception happened naturally.

A recent study found that for 44-year-old women, the chances of conceiving without medical assistance is 1.6 per cent.

The incredible luck of Bridges falling pregnant naturally is not lost on the Biggest Loser trainer.

"I feel very lucky," she told Who magazine, in its latest issue.

"But I also feel all of my years and all of Steve's years of looking after ourselves and taking care of our health and our bodies, it just goes to show. For someone my age, for it to happen so quickly, it's obviously got to do with good health."

This seems like common sense, but is unlikely to have made the difference, according to IVF Australia medical director Peter Illingworth.

"Being particularly fit and healthy has very little effect on getting pregnant in the first place," he says.

"It's a common frustration in women I see," Illingsworth says of women who have taken good care of their health but cannot get pregnant.

Would Bridges' level of health and fitness not have made a difference?

"Probably not, no," Illingsworth says. "The ageing of eggs goes on regardless of how fit and healthy someone is."

That said, he notes that being in good shape does have its benefits.

"Certainly it will enable her to deal with pregnancy better," he says.

Bridges and Steve Willis said they assumed they would have to have IVF.

"I was good to go and start the whole process," Bridges reveals. "I rang them up and said: 'Won't be needing that!' They were like: 'What!? It happens, but it happens pretty rarely'."

Exactly how rarely, Illingsworth says is unknown.

"No one has any idea what the statistics are for naturally falling pregnant at 44," he says.

"Many women at that age have resort to donor eggs, but it does spontaneously happen naturally."

Indeed, and Bridges and her partner Willis are thrilled.

"The main message for both of us is that we're really happy. We're really looking forward to it and it's a new chapter for us and we're really excited to have the opportunity to share it with our friends, family and Steve's beautiful children," Bridges says.

Fairfax Media