The reason Mary isn't a mum is heartbreaking.

This Victorian woman has paid an unimaginable price for her size

Mary Reid has never been able to have children due to her weight. She and her husband of 19 years, Anthony, have now missed out on the chance to have children because she believes that at 48 years of age, she is too old.

“Being overweight isn’t just stopping me from partying,” Mary told The Biggest Loser trainer Shannon during her emotional audition, “It’s actually changed my whole life.”

What makes Mary’s story even sadder is that she is the heaviest female contestant to ever compete on the show. She weighs in at 181.5 kilos.

It was during a trip to Fiji that Mary realised just how much her weight was affecting her. She struggled to walk around in the heat and staff had to order hear a golf cart. "I even couldn't walk to lunch which was about 300 metres from our room," she told The Australian. "The hotel staff thought the cart was a very nice offer but for me it was a light-bulb moment."

"When I got home I immediately applied to be on The Biggest Loser. It was getting ridiculous."

She and husband Anthony were planning to install ramps and rails into their home to cater for her large size. There wasn't one aspect of her life that her weight didn't negatively affect. "You have to work so much harder at everything when you're a big person," Reid says. "I would go to a restaurant to make sure they had a seat I could sit in because I can't sit in a chair that is normal size. If the seats weren't big enough I'd make an excuse and not go to the restaurant. Going to the movies was out of the question too."

Mary has battled with a sugar addiction, polycystic ovarian syndrome and high insulin levels.

The reason obese women find it difficult to conceive is because:

* Obese women metabolise more fat which leads to higher fatty acid levels in ovaries which can effect the development of eggs and the survival of any eggs produced;

* Overweight women produce too much estrogen which has the effect of a birth control pill;

* Polycystic Ovarian Syndrome is common in overweight women and can disrupt the release of new eggs;

* Body fat distribution can have a huge impact on fertility. Women with high waist-hip ratios have greater trouble conceiving;

* Extra weight can lead to an increase in birth complications such as miscarriage, still births, gestational diabetes and pre-eclampsia;

* Many fertility doctors refuse to assist obese women with fertility treatments and IVF until they are at a healthier weight.

This season the show will attempt to transform the entire town of Ararat in Victoria where most people are overweight. It was living here that allowed Mary to ignore her weight for so long.

'I've always been a big person. In Ararat, I wasn't 'fat Mary', I was just Mary. "People accepted me as I was and made allowances. There are so many big people. I was eating for comfort. The table was overflowing with food and it wasn't always good food. It was a habit of a lifetime. My husband married me as a big woman and so I saw no need to thin down. He loved me as I was."

The new season of The Biggest Loser starts on Sunday night at 6.30pm on Channel Ten and continues on Monday at 7.30pm.

Is it fair that doctors can refuse to treat obese women for fertility issues? Or should everyone get the same treatment, regardless of size?