Cancer growth in response to oestrogen
Some cancers, such as breast cancer, can grow in response to oestrogen, a hormone produced in high quantities during pregnancy.
"The cancer cells have receptors that take up the hormone oestrogen and this sparks changes within the cell, meaning the cancer can potentially accelerate," explains Dr Kieran Breen, director of research at the charity Brain Tumour Research.
"But we don't know if these receptors are present in brain tumour cells, or if a brain tumour cell will react to hormones triggered by pregnancy."
For Katie and her husband, Luke, 32, a learning development manager, this made the decision to have a baby the toughest of their lives.
The couple met in June 2012. "We clicked right from the start, and talked about wanting to settle down and start a family," she says. They married in July 2015, embarking on a dream honeymoon tour of the US. Three months later, they were given Katie's shocking diagnosis.
As Katie explains: "I'd suffered the occasional migraine over the previous year, but they weren't bad enough to worry me. On honeymoon I had a few moments of dizziness. I assumed they were down to low blood sugar. The headaches I blamed on too much sun and alcohol, or my hormones because I'd stopped taking the Pill."
Doctors diagnosed migraines
After the couple returned home to Stourbridge in the West Midlands, Katie started a new job as head of English in a special-needs school. Within weeks she was suffering from constant headaches, and she blamed the stress of her new job.
"One day I also experienced a strange pins and needles sensation, which spread from my little finger up my left arm.
"I went to the GP three times and saw different doctors, and they all diagnosed migraines. One day, the pain was so bad I vomited. My mum took me to A&E, but I was told it was migraine and given strong painkillers."
Four days after going to A&E, Katie was "so exhausted" she went back to the GP.
"This time, I saw a different doctor, who conducted tests including holding my hands out and walking in a straight line. I sailed through, but while he said he wasn't overly worried, he referred me for an urgent MRI scan."
Katie had the scan a week later, and was told it would take 14 days for the results.
"The next day, I arrived home at 7pm and my GP rang. She said: "We have found something; there is a lot of pressure on your brain, and you must go to hospital immediately."
"At the hospital, the doctors gave me a high dose of a steroid to reduce the swelling in my brain. Then one said: 'We are almost certain it is a tumour.'
"I felt utter horror - but I also felt relieved there was a reason for the terrible pain.
"The doctors were not sure if the tumour was cancerous or benign. But I had another MRI and a CT scan that night to see if it was a primary or a secondary tumour which had spread from elsewhere.
Telling her husband
"I said to Luke: 'You do realise that if it's secondary, I'm a gonner,' and we both had our first cry."
The tests revealed a 6cm primary tumour at the front of Katie's brain. She was transferred to the Queen Elizabeth Hospital in Birmingham, a specialist centre for neurological surgery, and a week later, Professor Garth Cruickshank, a consultant neurosurgeon, removed 90 per cent of the tumour in a five-hour operation.
A month later, she received the biopsy results: it was a Grade Two cancer, malignant but slow-growing. "I was so relieved I actually gave Luke a high five.
"But the professor said three things could happen: nothing may change; it could grow back and remain Grade Two - or it could grow back and become a high-grade malignant tumour. 'And there was a one in three chance it could return in five years."
Another bombshell
Katie was told to come back for another scan, so they could check the tumour hadn't returned. "Then, in an unfolding nightmare, my mum, Jan, was diagnosed with non-Hodgkins lymphoma at the end of January. Her condition is incurable.
"I realised her time was limited, and I wanted her to hold a baby of mine before she died.
"Luke and I talked endlessly about it. I didn't know if I should bring a child into the world knowing it was potentially going to lose its mum at such a young age."
When we returned to see Professor Cruickshank, I asked: "Can we start trying for a family now?" He said: 'If you are going to do it, now's the time.'
"I had just turned 30 and I asked: 'What are my chances of reaching 40?' He said: 'I think 50/50.'
"When we left, Luke just broke down and that was the hardest thing for me to see because he'd been so positive until that point."
Deciding to just live their lives
Over the next few weeks, Katie and Luke and I had many emotional conversations about whether they should try to have a baby: "In the end, we decided to go ahead and live our married lives as we would have done if we had not discovered the brain tumour."
Seven months later, in September 2016, Katie was pregnant. She is classed as a high-risk pregnancy because she has epilepsy - it's not clear whether it was brought on by the surgery or the tumour - and is being monitored closely.
To keep herself occupied as she recovered from her surgery, Katie entered a national competition, to write a children's book. Her book, The Pumpkin Project, won - "I couldn't believe it!" recalls Katie, "and now my book has been published."
Her baby will be delivered by elective caesarean on Saturday. "After he's born, I'll have brain scans every six months," she says.
"If the tumour grows, I could have chemotherapy and radiotherapy. I only plan six months ahead - up to the time of my next scan. I've accepted that I probably won't see my son's milestones."
As Kieran Breen explains, more research into brain tumours is desperately needed. "There are 16,000 new cases diagnosed in the UK each year, and they kill more children and adults under 40 than any other cancer," he says.
"Around 80 per cent of people with breast cancer survive up to five years after treatment; in brain tumours it's just 20 per cent."
Katie adds: "I don't know what will happen in the future. But no one can take the joy of my baby away from me."
