They like to say their family is two in a million.
For Alison Spooner and her partner Dean Durrant's offspring have defied the odds - not once, but twice.
Seven years after having one black twin and one white twin, the 27-year-old mother has given birth to a second set of twins with different coloured skin at odds of one in 500,000.
When the couple's first daughters arrived in 2001, they were astonished to see that Lauren had her mother's blue eyes and red hair, while her twin Hayleigh had dark skin and hair, like her father, Dean.
So when Miss Spooner, from Fleet, in Hampshire, found out she was pregnant again this year, her friends and family joked that they ought to take a bet out on the same thing happening again.
Doctors who delivered the sisters early, because of fears for their health, were relieved to find them well, but also amazed that the second set of twin girls were born with different skin tones.
As her parents discovered when the girls were laid side by side in the hospital cot, Miya resembles her father and Leah has inherited her mother's looks.
It is rare enough for two sets of twins to be born to the same parents, but the chances of them inheriting different skin and hair colour from their mother and father are just two in a million.
The genetic phenomenon only happens when two separate eggs are fertilised by different sperm, unlike identical twins who share their genetic make-up having been conceived from one fertilised egg that splits to form two embryos.
'I was shocked when I first found out I was pregnant with twins again - but I never thought for one second they would turn out the same as last time,' Miss Spooner said.
'After the babies were born they weren't breathing properly, so they were taken to a special care unit.'
The former recruitment consultant added: 'It wasn't until about five days after they were born that we saw them side by side for the first time.
'And when they were together it was clear that one was darker than the other. It was unbelievable.'
Doctors at Frimley Park Hospital, in Surrey, decided to deliver the babies on November 13 by Caesarean section, 37 weeks into the pregnancy, when scans revealed they were in the breech position.
This can cause complications during birth that can endanger the babies' lives.
However, despite their early arrival, both girls were born healthy, with Miya weighing 4lb lloz and Leah 5lb 10oz. Their father Dean, 33, a paver who is of West Indian origin, said: 'It was a real shock to the system when I found out we were having twins again.
'I didn't think the same thing would happen again.
'I was blown away when I saw them together. I didn't know until then that there was such a big difference between the two.
'It was clear to see but they were rushed away after they were born so we didn't realise until we saw them together. We have a very special family.'