In an act of selflessness, a mum has donated 500 ounces of breastmilk after her son died of a rare genetic disorder.

Sierra Strangfeld was just twenty weeks pregnant when her son was diagnosed with Trisomy 18. Born two months ahead of his scheduled due date weighing less than two pounds, Samuel Lee survived for just three hours before he passed away.

Samuel Lee was born by emergency C-section on September 5th, weighing one pound and seven ounces and measuring 12.5 inches.

It was then Sierra decided she would express her milk and donate it to a NICU breastmilk bank to help other mothers with babies born prematurely.

Trisomy 18, otherwise known as Edward's Syndrome is a chromosomal condition which causes deformities of organs and other body parts. In most cases, babies survive less than 24 hours after being born while just five per cent of babies with Trisomy 18 live for more than a year.

In a post on her Facebook page, which has since gone viral, Sierra said how she looked forward to breastfeeding, having run into some obstacles with her first child. 

"When I found out I was pregnant again, I wanted nothing more than to be successful at breastfeeding."

"But when we found out of Samuel's diagnosis, I knew that was not going to happen. Just another hope that was taken from me."

"Before Samuel passed, I told myself I would pump my milk to donate. After all, Porter was given donated milk more than half of her first year of life!"

The selfless mum knew she couldn't save Samuel's life but that she could save another.

"I couldn't save Samuel's life, but maybe I could save another baby's life," she said.

Any mother who pumps exclusively knows it's not for the faint-hearted. It's both physically and mentally draining at times and for Sierra, it was even harder because she didn't actually have a baby.

"There were times I was angry because why did my milk have to come in when I had no baby to feed? Why was I waking up in the middle of the night for this? The other part of me felt it was the only thing connecting me to Samuel here on Earthside. I sure hope he's proud of me!"

In total the mum from Neillsville, Wisconsin, pumped for 63 days after his birth and honoured her son's legacy by donating a total 14 litres of breastmilk to the NICU milk banks.

"Walking through the hallways of the hospital was just another step in healing. And I know, (because I felt him), that Samuel was there with me," she concluded.

Parents have been quick to praise her selfless act in the comments with others commending her bravery. 

One social media user wrote: "Thank you so much. As a former NICU nurse for 35 years, I know how valuable your gift will be to the many babies and families who receive the milk. Samuel's spirit lives on."

While another said: "First I want to say how sorry I am for your loss. You are a truly amazing woman. I don’t think many people could have done what you did for other babies after losing your child. I’m sure your baby is in heaven looking down on you proud of you."

The only milk bank based in Fermanagh, Ireland, which serves both north and south is always looking for new mothers to donate breastmilk. Potential donors are being asked to contact the milk bank at tmb.swah@westerntrust.hscni.net.