She married a twin, gave birth to twins and has first-hand experience of their closeness and innate connection.

"They have a shared history, but there is so much more to it than that."

When Athena met her future husband David - and shortly after his fraternal twin Paul - she was struck by how different they were.

"It felt like they were brothers, not twins," she said.

However, as the years have passed, Athena has become more aware of their need for close contact and the way they are constantly conscious of each other.

"It seems to me they are becoming even closer as they get older," she said.

While David was always open about his desire to have twins himself, "because they are the best", Athena said she thought the chances of that happening were almost impossible.

She was speechless when the sonographer found two identical twin embryos during an ultrasound.

"Dave was ecstatic."

William and Sam, now six, are every bit as close as their dad and uncle, but the work of caring for two newborns was more than David and Athena anticipated.

"When we had our second pregnancy, I think Dave was terrified of the prospect of two more. He wanted to have an early scan to be sure," she said.

Luckily, a daughter, Adelaide, arrived on her own.

Athena says she sees the same inexplicable bond between her sons as she sees with her husband and his brother, but concedes she doesn't understand it as easily as her husband does.

"They are best friends and it is lovely to see that they have each other, but I think Dave probably understands them better, and understands their relationship on an intuitive level."

Multiple Birth Awareness Week begins on Monday. The Canberra and Region Multiple Birth Association said the 2015 theme of "Together everyone achieves more" was an opportunity to raise awareness of support available to families adjusting to life with multiples.

Association president Karen Stewart-Moore said her own boy/girl twins were just over two and "we couldn't have got through the last two years as happily as we have without all the people who help to make our family life work," she said.

The association has been active for more than 40 years, offering regular events and activities to build friendships with people who really understand what life is like when multiple births join a family.

It also provides a virtual network through its active Facebook group and a range of volunteer support officers who can share experiences with issues like premature and caesarean birth, breastfeeding and bereavement.