"My husband and I realised that being parents was about caring for a child and nurturing them, whether we were blood-related or not," she told The Huffington Post UK.
"We loved that aspect of parenting, we didn't mind who the child was we just wanted to have that experience."
Saira Khan went through one round of IVF to fall pregnant with her son
When Khan found she couldn't fall pregnant, doctors told her she had endometriosis - a condition where tissue that behaves like the lining of the womb (the endometrium) is found outside the womb.
Khan was classified as having stage three endometriosis known as "moderate". Stage one is classed as "minimal" and stage four is "severe". Stage three is considered as an advanced stage, according to the Endometriosis Institute.
At stage three, there are "deep implants on your ovary and pelvic lining", which interfere with ovulation and the egg embryo transport, meaning it is very hard to fall pregnant. In the stages one and two women have more of a chance of conceiving naturally.
"It's quite a common thing in women, but I was told the only way for me to have children at this stage was through IVF - there was no alternative," she said.
Khan calls herself "lucky" because her first round of IVF worked and she gave birth to her son, Zach, in 2008.
Two years down the line when she wanted more children, she was told IVF would be the only option again.
Khan went through another cycle of IVF, but said she and her husband had already made the decision that if it didn't work the first time, they had a plan B.
"It didn't work, and we had no doubt in our minds that we weren't going to continue - we wanted to adopt," Khan said.
"I had spoken to a few people who had IVF and were on their fourth cycle, but I couldn't put myself through it again. It's an intense procedure and a gamble.
"Why gamble when there are so many children out there who need a loving home?"
The day Khan found out her second round of IVF had failed, she picked up the phone to enquire about adopting another child.
She and her husband visited the local council straight away and were referred to discuss things with a social worker.
However in a frank and open discussion, they were told it would be hard to adopt because the adoption process law says you can't adopt a child unless there is a significant two year gap between the two children. Zach was only just two at the time.
In order to have a big enough age gap between their children Khan and her husband would need to adopt a newborn baby, but they were told this would be hard in the UK and would take much longer.
Khan begun to think about alternative options.
"I come from heritage in Pakistan and I had visited an orphanage in Karachi two years prior to this and it made me think about intercountry adoptions," she said.
"I was told I could do that. Our local council outsourced the adoption process to the charity PACT and it was through them we managed to start the process.
"PACT were outstanding - they had time for us and genuinely engaged in making sure our adoption was how we wanted it."
The adoption process in Pakistan was slightly different, however. Khan had to go travel to the orphanage in Pakistan, unaware of what child she would be adopting.
She explained: "One of the things with intercountry adoption is depending on where you adopt, there are different rules.
"Pakistan is not part of the Geneva Convention, which basically means when you go over to adopt, you have to physically go to that country and make contact, following their rules and regulations.
"This means you have no clue or idea about what child you're going to get."
Saira Khan and her daughter Amara, now five
Once Khan and her husband had reached the final stage of the adoption process with PACT, it was time for her to go to Pakistan.
"I literally went out there to the orphanage and said 'Hi, I've been approved by the British government for adoption, my papers are with the British embassy and I've come to adopt a child from your orphanage," she explained.
Khan was told there were no newborns, so she should go to her hotel and wait until she was called.
Six days later, she received a call saying a baby girl had been left at the orphanage.
"I went in and sat and waited, and they brought a pink blanket over to me and put her in my arms," Khan recalled.
"What was really significant to me at this point was that I remembered everything I had been taught on the adoption course with PACT.
"I was elated, but nervous and anxious. I was given a baby with no medical record, no state of health and was told 'this is your child'."
Khan said PACT's advise parents adopting children from overseas to ensure that people are matched with the child they want and know they can look after them comfortably once in the UK.
"I was looking for obvious disabilities, at which stage we could decide whether we were going to go ahead with the adoption or not," she explained.
"Adopting children from overseas means that if the child had a disability and we knew about it before entering the UK, the NHS would not pay for any medical care for that child and the whole health bill would then have to be handled by us.
"So for example if it was discovered that Amara had HIV before entering the UK, even though we are British citizens our baby would not have access to NHS services for that condition and her whole treatment for life would have had to be paid by us.
"I had no idea what Amara's health condition was, but I fell in love with her immediately and I didn't care what her health condition was as I was committed to look after her no matter what."
The procedure that PACT ask all parents to carry out when they are handed a newborn baby includes:
Take off baby's clothes.
Look into baby's eyes to see if baby can focus.
Test hearing by clicking fingers.
Check baby's grip.
Check baby's spine, legs arms and head.
Check nappy area.
Take baby to hospital for blood tests.
Khan took Amara straight to the hospital in Karachi, where a paediatrician gave her a medical examination and she was told her daughter was very weak at just under five pounds. She wouldn't feed and was put in intensive care immediately.
Khan named her daughter Amara, a muslim name that means 'eternal'.
It took seven days for Amara to come out of intensive care.
"Once we were out of the hospital, I phoned my husband and he came out for four weeks with my son, now we knew that she was well and going to survive," she said.
"In total I was out there for three months. I had to stay out there for so long because she was left with no name, papers or identification.
"I had to get her identified and liaise with the embassy before bringing her back to the UK."
Khan said the whole experience was overwhelming, but she learned when you're a mother, you'll do anything for your child.
"I didn't see myself as brave," she added. "I'm a mother and I did what I could to make sure she was okay.
"Watching a child grow because of the love you give it and everything you put into it amazes me," she added.
"The power of love, you see that in an adoptive child - they're responding to your love, care and opportunities you provide."
Khan says adoption is an incredible experience, but she understands it's not something that works for everyone.
She said parents who are struggling to conceive should make sure they go and chat to a professional to understand if adoption is the right route for them.
But for those who are interested in this route, Khan said the adoption process in the UK is "outstanding" and gives parents the skills to cope with all eventualities, such as how to bring the topic of adoption into their children's lives and understanding what questions they will ask as they grow older.
"Zach and Amara are inseparable now and they adore each other," she said. "I might as well have given birth to her - she's a mini me.
"Adoption has been part of our family since we brought Amara home. I got a painting commissioned which tracked Amara's life from Karachi to Oxford.
"It takes pride in our room and Amara can look up at it and see every day of her life - adoption should never be a surprise to her."
Khan said she calls Amara's birth mum her "tummy mummy" and both Amara and Zach know they came from different mummie's tummies.
"Adoption has a big stigma," she continued. "But if you celebrate it and make it part of your life, it's not a big deal and we talk about it all the time."
Khan said Amara will never be able to find her tummy mummy because her identity is unknown, but she will never be forgotten about.
"Once a year, on Mother's Day, I think a lot about the mother who gave birth to my daughter," she said.
"I send her a wish and hope it gets to her because I don't know who it is, but I hope she feels her daughter is well looked after and is bringing so much joy to another family.
"She is the centre of our life. I send that wish and really hope it gets to her."