TV cameras follow woman's emotional journey to give her sister a baby

Growing up, Billie always dreamed of the day she'd become a mum.

"I was one of those little kids that like had their whole life planned," she told A Current Affair.

"And for me, it was like, when people would ask me, 'What do you want to be when you grow up?' My response was, 'I want to be a mum'."

READ MORE: Surprise pregnancy leaves Melbourne couple with four kids aged one and under

But when she was 12, she realised she'd never be able to fall pregnant.

"I was born without a uterus, but I still had ovaries and tubes, so I still could have my own biological child, because I didn't have that I just wasn't able to carry my own child," she said.

When she met husband Rob, becoming parents was a dream they didn't want to give up on.

So Billie's sister Shannon decided to volunteer to be their surrogate.

"Once I made that decision, like there was no going back," Shannon said.

Season three of Big Miracles follows the couple as they embark on their journey to parenthood.

This season details some of the most complicated fertility cases yet, like Ilina and Nick, who have already spent nearly $150,000 in their desire to start a family.

Season three of Big Miracles airs at 9pm tonight on Channel 9 and 9Now.

Watch the full video in the player above.