A US mum who gave birth to a baby weighing almost six kilograms has shared the moment she realised her little boy was larger than most.

Shelby Martin, from Tennessee, stunned the internet earlier this month when she took to social media to reveal that her son, Cassian, broke hospital records when he was born.

The little boy weighed a whopping 5.8kg — a huge 2.2kgs heavier than the average baby, which comes in at 3.5kg.

The hospital claimed that Cassian was the largest baby born there in the last three years following his arrival in July.

Ms Martin, who is mum to Elijah, 9, Waylon, 8 and Jonah, 7, said the family had been waiting a long time to meet its newest member. They had been expecting a baby a year earlier, but sadly on Ms Martin’s 29th birthday the couple were told that their baby no longer had a heartbeat.

It was an incredibly difficult moment for Ms Martin and her partner Joshua Thomas, 27.

So, when the couple discovered that they were once again expecting a baby, they were over the moon. The 30-year-old said she had the perfect birth plan all mapped out — including the wish for a vaginal birth, like all her other children.

However, when the couple found out their baby was measuring large at the 36-week scan, her dreams of a vaginal birth disappeared over concerns that Cassian could have difficulty during delivery.

“Sure, I grieved the loss of my ‘perfect birth plan,’ but looking back, I’m just so grateful,” she told.

However, she said she could have never predicted her little boy would be almost six kilograms. Ms Martin said that looking back at the pictures of herself during pregnancy, she probably should have known.

“Everyone was amazed by his size! He made such a big impression that nurses and doctors from all over the hospital came by the NICU just to meet him,” she said.

“He quickly became a little celebrity during his stay.”

Cassian was in the NICU for 10 days after his birth as, despite his size, he was actually born early. His lungs were slightly underdeveloped and his glucose levels weren’t steady.

It was the first time Ms Martin had any of her children spend time in the department. She said every time she visited the NICU, someone from the care team was already doting on her son.

She said it gave her a huge sense of relief and comfort.

Ms Martin said her three other kids were overjoyed when Cassian was finally allowed to come home.

“His three older brothers are obsessed with him, but I knew they would be. They have waited a long time for him,” the mum said.

Source: news.com.au