It's happening. April 21st 2013, I'm running the London marathon.

This might hurt.

Once again, I'm raising money for Bliss - the charity for premature babies and their families in the UK. About 80,000 babies are born early every year, which is dangerous for them and incredibly difficult for their parents. Bliss offers advice and support for parents, and funds research projects to try to improve the care available for babies.

Some of you will know that I was born very early, at 27 weeks - about three months before I should have been. I weighed about 2lb 8oz. I'm lucky to be here at all, and even luckier not to have any lasting side-effects.

As well as being premature I was a twin, which meant I was even smaller. My brother, Thomas, died the day after we were born. The incredibly cute photos you can see are of me in the weeks and months after being born as I recovered.

Obviously I don't remember any of this, although I did end up on Blue Peter because of it. My mum's written this to explain what it was like:

"I was 27 weeks pregnant and carrying twins when I started having contractions at home at night. The ambulance took me to the nearest hospital with a Special Care Baby Unit 35 minutes away. After a while being monitored there I was told I was going to have the babies and they were sending me in an ambulance to a hospital with an intensive care unit for premature babies an hour and a half away.

On route I started to need to push, and the ambulance diverted to another hospital where the babies were born. I glimpsed them briefly wrapped up in incubators before they were taken to complete their journey to the hospital with intensive care, where my husband, Mike, was waiting for them. I was not yet fit to travel and so stayed behind.

The next day, the news was broken that the first twin, Thomas, had died. He was too premature and his lungs were unable to breathe. Jamie, the second twin, was still fighting for his life in intensive care.

Jamie stayed in intensive care for about 10 weeks. He was dependent on a venilator at first and treated for jaundice. During this period we got to hold him about once a week, with oxygen being piped into his nose or given through a mask. There was the fear of infections, hydrocephalus or brain haemorrhage. Visiting the hospital was a round trip of 3 hours plus the time spent with Jamie. Monitors bleeped and sometimes alarms went off. Technical terms like bradycardia (slow or paused heartbeat) and apnoea (paused breathing) became everyday experiences.

After 10 weeks, Jamie was moved to a nearer hospital with ordinary Special Care, where he spent 6 weeks. The fear that he, too, might not survive began to recede.

Jamie came home at last after 16 weeks, attached to an apnoea alarm, which would warn us if he stopped breathing, and after a lesson on how to resuscitate a baby.

Jamie proved to be a fighter, and we're all very lucky that he has suffered no long-term effects from his difficult start in life. The hospital staff not only saved his life, but offered us vital support and encouragement, both over Thomas' death and Jamie's battle for recovery. Without medical expertise and technology he wouldn't be here today."

I have a pretty punishing training schedule lined up over the next few months, with the aim of getting across the finishing line in 3hr30m. It would also be lovely to see any of you who can make it at the finish line on the day, when I'll have my first drink since New Year's Eve :)

So if you'd like to support the continuing gradual erosion of my knees, here's what your donations will support:

• £10 provides crucial telephone support for a family through Bliss's helpline

• £25 buys a full set of information booklets for a family to help them understand their baby’s treatment and development

• £40 allows an overwhelmed parent to attend a counselling session with a Bliss-trained counsellor

• £100 provides essential training for a parent-to-parent volunteer

• £500 funds a Bliss parent support group for a whole year

I'm proof that premature babies can survive and grow up healthy - donating to Bliss will help them carry on their work and support more families at such a scary time.

Any and all donations will be massively appreciated - and if you're a UK taxpayer, please add on Gift Aid too!

Jamie x