Doctors discovered that both Julia Eynon and her husband Stuart had abnormal chromosomes which were being passed to their unborn babies, causing Julia to miscarry.
Tragically, Julia, 37, had lost two sets of twins before doctors made the heartbreaking discovery.
Using a special 'designer' technique doctors selected embryos which were free from the abnormal chromosomes that were causing her to miscarry, and implanted the embryos in Julia's womb.
It meant that her twins Holly and Aaron were able to be born safely in March last year.
Julia, a health visitor, says: "The doctors had told me it was unlikely that I could ever give birth to a baby alive, it was heartbreaking.
"We both had faulty chromosomes that meant that when I fell pregnant, the baby would either miscarry or die at full term, before I could give birth.
I thought I would never be a mum - but now my twins have been born safely due to this wonderful technique.
It seems like a miracle."
"I thought it would happen straight away," explains Julia. "I came off the pill and expected to fall pregnant within a few months. But nothing happened, so I went to see my GP who told me to be patient and that it can take a while and not to worry."
But by Christmas the following year, Julia still hadn't fallen pregnant so she went for a scan and doctors discovered she had polycystic ovaries. She was put on the fertility drug Clomid for a further 12 months, but still nothing happened, so the couple were referred for IVF treatment.
They underwent their first cycle at IVF Wales in Cardiff in January 2008, and it was a success. Doctors put two embryos back into her womb, but then at six weeks she miscarried both the twins.
"We were absolutely devastated. We had thought that after the years of trying, we were finally going to be parents. When they told me I was pregnant I was overjoyed. So to lose both the babies at six weeks was heartbreaking."
But again at six weeks she miscarried and lost both babies. Devastated, she asked the doctors to carry out tests to see why she had lost both sets of twins.
The tests showed that both Julia and her Stuart, 39, a supplies coordinator for St Johns ambulance, were carriers of abnormal chromosomes - one which caused early miscarriage, and the other which causes the baby to die at full term.
"We were both devastated when we were told the news," says Julia. "It meant it was unlikely that I would ever be able to give birth to a baby that was still alive. It was heartbreaking to think that it had caused me to lose both sets of twins."
It means that they could test for the two abnormal chromosomes in the embryos and make sure only ones unaffected would be used.
"We had never heard of the technique before, but it meant that we could have a baby without these abnormalities, so we decided to go ahead," says Julia. "It was our only chance at being parents."
The couple underwent their fourth cycle of IVF in June 2010 and this time all the embryos were tested, but they were all found to have the genetic fault.
In September 2010 they had a fifth attempt, and this time seven of the 15 embryos were found to be free of the defective chromosomes. Two were put back into Julia's womb and were successful:
"I was so thrilled when I found out I was pregnant, and now this time I knew that the babies had a much better chance of developing normally."
"After everything we had been through to have the twins, we really thought that they were going to die. It was devastating."
Doctors gave her steroid injections to develop the babies' lungs whilst they were still in the womb and Holly was born first weighing just 2Ib, followed by Aaron at 2Ib, 4oz.
"They were so fragile and tiny. Holly had a perforated bowel and Aaron had a brain haemorrhage," says Julia.
"But they were both real little fighters and hung on. We just had to pray that after everything they had been through they would be alright."
The twins were finally allowed home after three months and are now coming on in leaps and bounds.
"They are doing so well now. They both have great appetites and they are getting much stronger," says Julia.
"We feel so lucky to have them, and we are just so grateful for the 'designer' technique that allowed them to be born."
Words: Lucy Laing at Worldwide Features
More on Parentdish: Pregnant mum spends five months in bed to save lives of unborn twins
Suggested For You
Get top stories and blog posts emailed to me each day. Newsletters may offer personalized content or advertisements. Learn more