Identical twins are a source of fascination to many people and account for around 1 in 500 births in Australia. As we delve into the lives of three sets of identical twins, we discover one common thread — their bond for each other.

Preston and Nash

It was at a friend's baby shower when Mount Gambier's Amanda Davis noticed signs of a strong connection between her 13-month-old identical twin boys.

Cuddled and adored by friends on separate sides of the room, the brothers only had eyes for each other.

"They both howled," Ms Davis said.

"They were looking for each other. Like a baby looks for Mum and Dad, they look for each other."

Out and about in their pram, the cheeky twin boys are a beacon for strangers. ( ABC South East SA: Kate Hill )

Preston and Nash were delivered by emergency caesarean section in February last year — 10 weeks before their due date — and were rushed to Flinders Medical Centre neonatal unit for specialist care.

It was a happy, yet bittersweet, time for parents Amanda and Craig.

Three years earlier, the Mount Gambier couple had said a heartbreaking farewell to identical twins, Lila and Harper, born prematurely at 20 weeks. Sadly, the babies died minutes after their birth.

The odds of having two sets of identical twins in one family is around 1 in 300,000. Both sets of twins, and the Davis's two-year-old daughter Violet, were conceived through IVF.

Just a handful of family members can tell the twins apart.

When the Davises head down Mount Gambier's main street with their enormous twin pram, delighted strangers make a beeline for the baby brothers.

"I usually can't get from the car into the shops without someone stopping me and saying 'Oh, you've got your hands full' or 'double trouble'."

Although the focus is always on their physical similarities, to Amanda and Craig Davis the boys are two individuals with deeply different personalities.

Nash, born one minute ahead of Preston, is always a week or two ahead of his brother, the first to have his oxygen removed, the first to sit and crawl. Nash has eczema, while Preston does not.

Preston is chattier than his brother, while Nash is the first to burst into tears.

"People always think they are the same, but they are completely different people," Ms Davis said.

"They look for each other." Identical twins Nash and Preston at home in Mount Gambier ( ABC South East SA: Kate Hill )

The power of two

Although the Davis brothers are barely past their first birthday, they are already in hot demand for studies by universities and fertility clinics.

Both identical and fraternal twins are considered a valuable resource to scientists and medical researchers, their 'power of two' leading to ground-breaking insights and major findings into epilepsy, smoking and breast cancer.

"Twins put a magnifying glass on what it is to be human," said Professor John Hopper, director of Twin Research Australia.

"You can answer questions about genetic and environmental causes of health and wellbeing in a much more efficient way."

Formerly the Australian Twin Registry, Professor Hopper said the 37,000 twin pairs on the books of Twin Research Australia generously donated their time to be studied and questioned about their lives in the name of medical research.

"It is probably the nation's largest volunteer resource. It's an enormous cost-saving enterprise, which takes medical research forward," he said.

Elise and Emily

"We just understand each other." Identical twins Elise and Emily Fantin. ( Supplied: Elise Fantin )

"We have a saying: 'The world is right again when we're back together'," Emily Fantin said.

"I can go out and do my own thing and have my own friends but when I am with Emily, it just feels right," Elise Fantin added.

"You have someone who completely understands you and has all those shared experiences."

Growing up in Adelaide, the twin sisters did everything together. They played netball on the same team, learnt to drive together and even got jobs at the same bakery.

At the end of school, the sisters went their separate ways for the first time, heading to different university campuses to study different courses.

"It was the first time I was just Elise and Emily was just Emily," Elise said.

Although Elise now lives in Hobart and Emily calls Canberra home, the sisters make time for each other, acting as twin travel buddies on overseas trips and always, always spend their birthday together.

Although both sisters say it would be nice to walk down the street together unnoticed, they are used to curious and sometimes invasive questioning from complete strangers.

"Can you feel each other's pain?" is a common query.

Same tartan frock but different colours. Elise and Emily Fantin as children. ( Supplied: Elise Fantin )

Elise says the best explanation is that she gets a "gut feeling" when Emily needs her.

"If she gets hurt, it's not like I get a reciprocal sensation, but you have a feeling and you just know."

Enter a major shift in the twins' lives — a man.

Emily got engaged in October last year and next January, Elise will be matron of honour as her sister gets married.

Elise said the initial shock came when her sister first told her she was dating someone special.

"Then I thought, 'Oh, I have to meet this guy and make sure he's good enough for her'," she said.

"To his credit, early on he figured out that if he wanted a future with Emily, he needed to understand our relationship."

Both her husband and her twin will be important parts of her life, Emily said, but both agree that one day their lives will bring them back together.

"I've learned to share her," Elise laughed.

"I'll always be her twin and we'll always have that close bond."

Fractured twin relationships

Professor Hopper said articles and media dwelling on the special bond between twins often leaves those twin pairs who do not share such a close relationship feeling left out.

During his 30 years of studying twin pairs, one of his favourite lines of questioning is how they coped with being a twin and the answer may surprise many.

"They're always referred to as 'the twins', not as an individual and that is a big issue for twins," he said.

"One twin wrote to us and said 'Can you please take my name off the registry' because every time I get a letter from you, I'm reminded of her.

"We often see the twins who like each other, but there are twins out there for whom being a twin is a problem."

Like all relationships, Professor Hopper said the twin relationship changed at different stages of life.

"The word identical is a problem because it means genetically identical. It doesn't mean they are identical in everything."

Mollie and Trudy

Mollie and Trudy out and about shopping. ( Supplied: Kerry Woods )

"We are as strong as concrete," declares Trudy Hammond, when asked about her relationship with identical twin sister Mollie Woods.

Indeed, the 100-year-old pair — believed to be among Australia's oldest identical twins — say "We feel like one person".

Unbelievably, the New South Wales sisters only found out this year that they are actually identical.

Genetic testing revealed the twins have identical DNA. But the test results just confirmed what the pair already knew in their hearts, Mollie's daughter Kerry Woods said.

"My sisters and I have always said we have two mothers. Everyone says they sound the same and look the same," Kerry said.

The sisters both worked as magazine fashion illustrators, loved to draw and paint and got married in the same Liverpool church in the same wedding dress.

"I often heard them say 'You can't get between us and the two husbands never tried'," Kerry said.

The duo finish each other's sentences, they like and dislike the same things, have the same taste in clothes, and share an oftentimes dark sense of humour.

Twin sisters Mollie and Trudy as young women. ( Supplied: Kerry Woods )

Their husbands, who died in 1996 and 2011, are buried in the same cemetery but in different sections and Mollie and Trudy's final resting places has become a subject for debate.

"Mollie has a spot reserved next to Wally's ashes, but Trudy's husband Reg's ashes are in a commemorative WWII wall," Kerry said.

"Trudy has always said 'There's no spot for me, where will I go?'"

In their later years, illness divided the pair.

When she was 52, Mollie was in a serious car accident and the injuries left her with arthritis.

Trudy had breast cancer at the age of 84 and had a mastectomy.

The sisters now live two hours apart, but Kerry drives Trudy to see her beloved sister every few weeks.

The bond is so strong, a mere look or a raised eyebrow speaks volumes, but their differences balance them, Kerry believes.

A bottle of red wine often comes out when the sisters get together and there are still laughs when the nursing staff slip up and mistake Mollie for Trudy or vice versa.

"They just love being together," Kerry said.

"My mother just comes alive when Trudy is there. It's really nice to see."