One treatment even resulted in Wendy falling pregnant with quintuplets, but she sadly lost all five babies.
So after 20 years of heartbreak, the couple decided to go for one last attempt at fertility treatment with their one last frozen embryo. But when Wendy was lying on the scanning table at the fertility clinic before the embryo had been implanted, doctors made an amazing discovery.
Wendy had actually fallen pregnant naturally - after more than two decades of failed fertility treatment.
She has now given birth to their miracle daughter Olivia.
Wendy, 41, an office manager, married to John, 43, a security guard for the MOD, says: "I can't believe that I'm actually a mum at last. We went through such an emotional strain having 20 years of fertility treatment. We tried everything as we were so desperate to be parents.
We had decided to have one last attempt as I'd gone past the age of 40, and we just couldn't believe it when I was pregnant naturally, after all that heartbreak. To be a mum at last was something I never thought would ever be possible.
The couple decided to start trying for a family after their wedding in August 1987, and thought they would have no problems conceiving.
"We never imagined that it would be difficult. I thought I would fall pregnant within a few months," says Wendy. "We wanted to be young parents and we both wanted to have a family, so we didn't waste any time."
But after a year of not falling pregnant, Wendy decided to visit her GP, and tests showed that she was suffering from polycystic ovaries. She was put onto fertility treatment and had to start taking tablets, then injections, to stimulate her ovaries to produce eggs.
"We were convinced that with this treatment, I would definitely fall pregnant," explains Wendy. "But still nothing happened. I never fell pregnant, despite all the treatment."
We had been on holiday and I wasn't feeling well. So when I got back I did a pregnancy test and we couldn't believe it when it was positive. I was actually pregnant.
Wendy went for a scan at the Friarage Hospital in Northallerton - and there doctors made a shocking discovery. She was pregnant not with just one baby - but five.
"I was lying on the scanning table and the doctors just said to me that it looked like there was more than one baby in there," says Wendy. "I was so excited as I thought I was carrying twins. After all these years of trying, I was going to have two children at once.
"But then they carried on counting, all the way up to five. I was pregnant with quints."
"It was devastating to watch the heartbeats being extinguished one by one. But I knew I had no choice. I wouldn't be able to carry five babies safely," says Wendy.
But then three weeks later, Wendy miscarried the remaining twins, and lost so much blood that she had to have an emergency transfusion:
It was heartbreaking. We couldn't believe it. I had been pregnant with five babies, and now I had lost them all. We were both devastated. Everywhere I looked, there were mums with babies and pushing prams. It just seemed like I would never be a mum.
Over the next four years, the couple then had two cycles of IVF treatment on the NHS and two cycles that they paid £7000 for.
Two of the treatments failed, and after two of them Wendy fell pregnant, but miscarried on both occasions:
"It was a real strain on us both as a couple, as we wanted it so much. I even told John he could leave me as I couldn't give him a baby, but he refused. Then I tried homeopathy treatment too for a year to try and help me conceive, but that didn't work either."
In March 2006, the couple had another course of IVF treatment, costing £5000, at the Cromwell Clinic in Darlington, but that failed too. It left them with just one remaining frozen embryo.
"We were on the verge of giving up completely. We had tried for 20 years without success, and had every fertility treatment imaginable," says Wendy.
I had celebrated my 40th birthday, so I felt I was getting too old to carry on. But we talked about it and decided that we would try with the one remaining embryo and that would be our last chance.
But when Wendy started her tests before the treatment, doctors made the most amazing discovery. She had fallen pregnant naturally, and was six weeks pregnant.
"I was just in complete shock. I couldn't even speak I was so shocked. I went into the car park and phoned John to tell him," says Wendy.
The pregnancy was not without drama, and Wendy had a scare when she was nine weeks pregnant when she began to bleed, but scans showed the baby's heart was still beating.
"It was so emotional when I finally held her in my arms - we were both in floods of tears," says Wendy. "After 20 years of fertility treatments, we finally had our miracle daughter, and I was a mum at last."
Congratulations Wendy and John, enjoy your gorgeous daughter!