Rachael said: 'I never accepted that I wouldn't be a mother. I was determined to do anything I could to have a baby. And now I finally have my beautiful daughters, I feel complete. It has been worth all the heartache to have them with us after everything we have been through.'
After years of unsuccessful fertility treatment Rachael was finally discovered to be allergic to her husband's sperm.
She met Mark, 40, a car parts designer, in 1997 and the couple were married five years later, in March 2002.
They immediately started trying for a family after their wedding but nothing had happened after six months so Rachael went to see her GP.
Rachael, from Coventry, said: 'He said it was nothing to worry about and to keep trying, so that's what we did.'
Doctors told them they couldn't find anything wrong, and just to keep trying.
She said: 'I was convinced that something must be wrong as we had been trying for more than two years and I still hadn't fallen pregnant. But the doctors just said it was unexplained infertility and to keep trying.'
Mark then had the opportunity to work in Los Angeles, and they decided that fertility experts in Los Angeles may be able to help them.
Rachael said: 'We decided that fertility techniques may be more advanced over in Los Angeles, so we thought it would be a good idea to move and register with a fertility clinic over there.
'I was just desperate to be a mum and even though it was a long way to go, we decided it would be worth a try.'
After the 5,500 mile move, the couple visited experts at California Fertility Partners in Santa Monica and they tried four cycles of artificial insemination, but none of those worked.
Then in September 2006 they underwent their first course of IVF treatment.
She said: 'I was so hopeful this time that I was actually going to be a mum at last. I produced lots of good quality eggs and three perfect embryos were put into my womb.
I fell pregnant but I lost them all at five weeks. The doctors said there was no explanation for it, it was just one of those things. We were both heartbroken.
They underwent their second try at IVF in January 2007 but again that didn't work. So Rachael started researching on the internet for infertility problems and came across an article about natural killer cells , which can be present in the body and they destroy foreign objects.
The clinic carried out tests and found that she did have a high level of the killer cells in her body. A third course of IVF treatment was carried out, which again failed.
Rachael said: 'More tests were carried out and they found that I had the killer cells in my uterus, which was unusual. So my babies were being attacked from all angles. It was devastating.
'Another problem was identified too, which meant that my body was in effect allergic to my husband. It was attacking his DNA cells in our babies.'
Then the couple travelled to Mexico for Lymphocyte Immunisation Therapy, to inject Mr Sadler's white blood cells into his wife's body.
Rachael said: 'They needed to stop my body treating his cells as foreign bodies. I needed to stop my body being allergic to him.'
The couple travelled to the Mexico clinic five times - clocking up another 5,000 miles in their battle to be parents.
The treatment worked, but her body still continued to produce the high levels of killer cells. She then underwent a course of treatment at £5,000 each time to try and reduce the number of killer cells.
The couple then underwent a fourth course of IVF in December 2008 and, to their delight, discovered Mrs Sadler was finally pregnant with identical twins.
She said: 'We were so happy, We really thought we were going to be parents at last.'
But then tragedy struck at 14 weeks when doctors discovered the twins umbilical cords had become tangled, cutting of each other's blood supply, causing them both to die in the womb.
Rachael said: 'We were utterly heartbroken to lose the twins. We had finally thought we were going to be parents at last, so to lose our babies like that was devastating.'
After their loss, the couple decided to come back to the UK to try more fertility treatment, so they travelled another 5,500 miles back to Coventry.
In October 2009, they visited Care Fertility at Nottingham, and expert George Nwadke said he could help them.
Rachael was given more treatment to reduce the number of killer cells in her body, and then they underwent their fifth course of IVF treatment in April last year.
Two embryos were put back into her womb and six weeks later she discovered she was pregnant with twins.
She said: 'I was nervous after what had happened last time, but as my bump grew each month it was wonderful.'
Luckily her pregnancy went smoothly and her twins daughters were born in December, Rebecca weighing 6lb 1oz and Hazel weighing 5lb 8oz, at Walsgrave Hospital in Coventry.
She added: 'It was the most amazing moment in my life when I finally held them in my arms and I was a mum at last.
'We have travelled all around the world on an incredible journey and spent more than £70,000 to have our babies. But finally it has been worth all the heartbreak.'
Dr George Ndukwe, Medical Director, at CARE Fertility, Nottingham, said: 'The level of Rachael's immune abnormalities were the highest I have ever seen, and the most likely cause of her miscarriages and failed treatments.
'We are delighted to have helped after such an emotional journey.'