First, biological mother Amy Bernaba gave birth to Lauren, weighing 7lb 10oz, then, half an hour later, surrogate mum Torry Keay delivered 7lb 3oz Hannah.
The double pregnancy happened after Mrs Bernaba and husband George had undergone IVF treatment for 12 years in an effort to conceive a baby brother or sister for their son Jeremy, now 15.
Eventually, doctors decided that 40-year- old Mrs Bernaba would almost certainly be unable to carry another baby because of a problem with her immune system.
So they tried an extremely unusual procedure, implanting eggs fertilised by Mr Bernaba's sperm into her womb and also into surrogate Mrs Keay's.
Mrs Keay became pregnant, and against all the odds so did Mrs Bernaba. Both women had straightforward pregnancies before giving birth on May 27 in neighbouring rooms in a Los Angeles hospital.
Mr Bernaba, who runs his own security business, saw Lauren delivered by Caesarean section before doctors told him Hannah was on the way.
He raced to watch her arrival and took photographs to show his wife.
Yesterday, the couple told of their joy as they settle in to life at home in Beverly Hills with the twins.
Mrs Bernaba said: "I feel so happy to have them. I can't stop smiling.
"All the strain and heartache I've been through in the past few years have definitely been worth it, just to have these very special twins."
Although the twins are not identical because they came from separate eggs, they look very alike and Mrs Bernaba said she is only now starting to tell them apart.
"They both have dark brown hair and big blue eyes, but Hannah has gold streaks in her hair and her eyebrows are slightly lighter.
"She is the lively one, while Lauren is more quiet and relaxed."
Mrs Bernaba was 24 when she gave birth to Jeremy, and the pregnancy "just happened". It was only two years later when the couple tried to conceive again that her complex fertility problems emerged.
The Bernabas spent thousands on 14 IVF attempts which resulted in only one pregnancy.
Tragically, an ultrasound scan at four months found the baby had not developed properly and had to be aborted.
Finally, Mrs Bernaba was treated by U.S. fertility doctor Dr Michael Vermesh, who has one of the world's highest IVF success rates at 50 per cent.
Dr Vermesh also produced an earlier world first when he helped a woman give birth using an embryo frozen 12 years before.
The Bernabas contacted mother-of-six Mrs Keay, 31, via a friend, and she immediately agreed to help. Mrs Keay, a hairdresser, lives in Lake Arrowhead, three hours away, with her husband Billie, who runs a construction company.
She was paid an undisclosed sum to act as surrogate.
She said: "I immediately knew I wanted to do it and Billie supported me. We have a big family and we love children and we felt so sorry for people who weren't as lucky as us.
"I was excited to be helping somebody and when we met Amy and George and saw what a lovely couple they were, we were even more convinced."
The two women, who are now close friends, had their prenatal appointments and scans together.
Doctors decided to induce Mrs Keay so she would give birth at a similar time to Mrs Bernaba's Caesarean delivery.
Mr Bernaba, 40, said: "It was really quick. They had just cleaned up Lauren and we were holding her, when they said Hannah was being born.
"They handed the baby straight to me, so I could take her to see her mum and her twin sister."
Mrs Bernaba said: "We are going to tell the girls exactly how they were born and make sure they know they're both as special as each other."
The idea of implanting a woman's embryos into the mother and a surrogate at the same time is still extremely rare.
There has been only one other set of twins born this way, Americans Connor and Cameron Payne, who were born to mother Kathy and surrogate Angel Willis 16 days apart last June.
