It is the story of an improbable modern family - a back-to-front love affair where a woman seeks out and falls in love with an anonymous sperm donor who fathered her baby daughter.

In 2011, Aminah Hart was 42 and single and had lost two young sons to a rare genetic disorder that she eventually learned was passed on via a defective gene she carried.

Legislative changes passed in Victoria the previous year had opened up access to IVF for single women, giving Ms Hart one last chance of becoming a mother to a healthy baby.

"It takes the romance out of it a bit, doesn't it, when you decide to take on donor sperm to try and have a baby," Ms Hart said.

"It wasn't going to be picture postcard, being single, but I was raised by an amazing single mother and she taught me that I could do it."

Ms Hart was provided the details of three anonymous donors – just "three bits of paper" on each - detailing vital statistics, physical qualities, medical history and hobbies.

"And that's kind of it," Ms Hart said. "You're making a choice on who the father might be."

As she says in tonight's episode of Australian Story, one of them stood out.

His name was Scott. He was a cattle breeder who coached AFL football. He was a father of four. And he described himself as "happy and healthy".

"I thought happy and healthy - they're two things that just have eluded me, and so I locked it in [and] booked a date for the clinic," Ms Hart said.

'Why wouldn't you help someone?'

Scott Andersen first donated sperm in 2006, following an anonymous request that he initially dismissed as a joke.

"And then I thought [that] people give blood and all that. Why wouldn't you help someone?" he said.

With demand far outweighing supply, Mr Andersen then agreed to the IVF clinic using his donation to assist other conceptions.

Aminah (pictured with her father Tony) was raised in Australia after her parents' relationship failed in the UK. ( Supplied )

Ms Hart had given birth to two children before she attempted IVF using donated sperm.

Her first son, Marlon, was born "floppy" in 2005 and, despite a series of tests, there was never a diagnosis. He died at 14 weeks.

When Louis was born in 2008 "blue and floppy", Ms Hart knew it had happened again and that it was something she had passed on to her sons, as they had different fathers.

Louis was diagnosed when he was 17 days old with X-linked myotubular myopathy.

"[It's] a condition where the muscles don't have any contractile ability so they can't breathe properly, they can't swallow, all their muscles are very floppy. And that is catastrophic," Ms Hart said.

It is passed on to 50 per cent of boys born to a mother who is a carrier, but it is not manifested in girls.

Louis lived for "14 great months" but after his death, Ms Hart wrestled with the difficulty of "being a mother without kids".

She said IVF using anonymous sperm donation was her last chance for motherhood.

Gender left 'in the lap of the gods'

Gender selection is legally possible when there is a high risk of inheriting a gender-related genetic disorder.

However, the process also runs a risk of destroying the embryo - a possibility considered too risky for Ms Hart, who decided "to leave it in the lap of the gods".

Ms Hart said she cried when she discovered she was pregnant and was relieved the baby was a girl.

When Leila was born in 2012, Ms Hart said the first thing she noticed was her healthy cry - and the next was her blond hairline.

"I thought 'I can't have a blonde baby, I'm a black woman. Black women don't have blond babies'," she said.

Ms Hart was born in London in the late 1960s to an Australian mother and a West Indian father.

"I met Tony, Aminah's father, at a party in London. He'd just come back from filming in Jordan, playing Omar Sharif's bodyguard in Lawrence of Arabia," Ms Hart's mother, Helen Marshall, said.

"So that was a fascinating thing for a young Aussie."

The relationship deteriorated after Ms Hart's birth, so Ms Marshall returned to Melbourne to raise her daughter.

Ms Hart describes her family life as happy, but said she "got a lot of flak for being from a single-parent family, being black".

"So even though I grew up very Aussie, I knew Dad was the black part of me," she said.

"I really just did have this sort of underlying notion, when I'm ready, I'll go and find him."

When she did eventually go to live and work in London as a young advertising account executive, she learned that her father had died not long before her arrival.

"I call myself half West Indian," she said. "And so the notion that I was not ever going to be able to delve into that from the person who was the other part of my history was quite devastating."

Curiousity grows, contact is made

She said not knowing her own father made Ms Hart doubly curious for more information about her daughter's donor father.

In the meantime, her mother claimed to have uncovered the donor's identity and photo after googling details included on his donor form.

So Ms Hart requested contact via the donor-recipient voluntary register.

Aminah Hart (2nd row, 4th from left), who went to school with Cate Blanchett (2nd row, 3rd from right), described her upbringing as happy. ( Supplied )

The Victorian Assisted Reproductive Treatment Authority (VARTA) says "donors can only donate on the basis they are not anonymous".

Donor offspring and their parents are legally entitled to information that identifies the donor when the offspring turns 18. Prior to that, they can request information via a voluntary register.

At the time of his donation, Mr Andersen said he ticked the box on his donor form that gave consent for recipients and offspring to contact him prior to them turning 18.

However, he said he never thought he would ever meet any children until he was "elderly".

When the email and photos of Leila lobbed into his inbox, Mr Andersen – a twice-divorced father of four – "didn't know what to think, it didn't seem kind of real".

But he agreed to meet when Leila had just turned one.

"I was nervous and tentative but the rapport was really easy," Ms Hart said.

"The first thing for me was 'phew, he's a nice guy'."

Love blossoms in ready-made family

Mr Andersen said he could see a lot of his sons' features in Leila. Both Mr Andersen and Ms Hart wanted Leila to have an involved dad.

The growing relationship with Leila and Ms Hart caused conflict between Mr Andersen and his partner, eventually leading to their break-up.

Not long afterwards, Ms Hart and Mr Andersen began a romantic relationship.

VARTA says "there's no established etiquette" when it comes to donor-recipient relationships and that it is "all new territory".

Kate Bourne, VARTA's donor registers service manager and chair of Australian New Zealand Infertility Counsellors Association (ANZICA), said there was very little research done on the connection between donors and recipients as only a minority of people currently seek access to the voluntary register.

However, there is a growing number of donor linkings. From a counsellor's perspective, it is "a new and emerging interest".

From June next year, VARTA will be "offering support to donors and their extended families, including their partners and children, on how to manage the linking process to ensure positive and sustained contact".

Together for nearly 12 months now, Ms Hart and Mr Andersen continue to live in separate towns – Ms Hart in Melbourne and Mr Andersen breeding cattle on two properties near Phillip Island – but they co-habit and co-parent most days of the week, with Leila being an only child in Melbourne and the baby sister of four near Phillip Island.

"Having the donor child as the final sibling in the family is a very modern twist, isn't it?" Ms Hart said.