Sharon Darke, who lost her twin babies more than 20 years ago, is running the marathon in aid of the charity - Twins Trust.
She said: "My twin boys Charlie and Joshua died 22 years ago, and I was initially supported by them and now work as the bereavement group coordinator."
Sharon has launched a Just Giving fundraising web page to help the charity, and raised £800 towards her £1,000 target.
You can contribute to Sharon's London Marathon fundraising challenge for Twins Trust using the following web link: https://www.justgiving.com/fundraising/sharon-darke6She added: "I am running with over 250 babies names on my running vest, mostly twins and triplets from our group.
"I am lucky enough to have my second ballot place this year at the London Marathon. I am going to raise money for Twins Trust bereavement group in memory of my twins Charlie and Joshua.
"Sadly twins and triplets are more likely to die as a result of stillbirth or neonatal death. Twins Trust is committed to undertaking research to better the lives of our families and improve the health outcomes from multiple pregnancies. They aim to stop 580 babies dying by 2022 and 1,100 from needing neonatal care."
Sharon, who is from Middleton Cheney, is an active member of the Cherwell Runners and Joggers club. She also ran the London Marathon in 2019, and raised money to help Tamba – the Twins and Multiple Births Association (now Twins Trust) – and Oxfordshire Children’s Diabetes Fund. In 2017, she undertook 18 challenges over 18 days for what would have been Charlie and Joshua’s 18th birthdays, raising money for Tamba.
Sharon added: "I received the best support from Tamba (now Twins Trust) after Charlie and Joshua died, and now feel privileged to work for them and to support bereaved families after their loss."