A Utah mom has been shopping for larger diapers after giving birth to a 14-pound baby boy.

Sara Brandon gave birth to her son, Joel Brandon Jr., or "J.J.," by cesarean section last May and was shocked by his size, especially since her last ultrasound estimated his weight as closer to 11 pounds.

"When they stuck him on the scale he was 14 pounds even," Brandon told ABCNews.com. "The doctor said it was the biggest baby he had ever delivered."

J.J. Brandon weighed 14 pounds as a newborn. (Courtesy of Sara Brandon)

The delivery was a bit different from Brandon's previous birth experience with twin girls. Each girl weighed 4 pounds, and together they still weighed 6 pounds less than J.J.

"I had to have two [obstetricians] deliver him instead of one, because they knew he was going to be big," said Brandon. "They struggled to get him out."

According to Dr. Robert Barbieri, chief of obstetrics and gynecology at Brigham and Women's Hospital in Boston, J.J. was more likely to be oversize because Brandon has type 1 diabetes.

"An interesting effect of insulin, if it's not taken in a sufficient amount, the glucose remains high, and the baby's glucose starts to rise," said Barbieri. "It's like giving the baby fertilizer and it grows very large."

Barbieri said approximately one out of 1,000 babies could weigh 11-pounds, and one out of every 100,000 could weigh 14 pounds. A 14-pound baby, he said, is extremely rare, because usually a doctor will induce labor if a baby appears oversize.

J.J. spent the first 10 days of his life in the neonatal intensive care unit because of lung problems, said Brandon. But since he's left the hospital, he's thrived.

"He's very calm, content and giggly. He sits with his sisters all day. He only cries if he's hungry or tired," Brandon told ABCNews.com. "He's an awesome little guy, or big guy."

13-Pound Baby Born Naturally in Germany

Brandon said that J.J. and the now 3-year-old twins can all wear the same size diaper in spite of the age difference.

Cases of women delivering large babies vaginally appear to be grabbing headlines in recent years. A 13-pound baby was born vaginally in Germany in July, and a baby weighing nearly 14 pounds was born vaginally to an Iowa woman in 2012.

But these hefty newborns pale in comparison to the baby born to Guinness World Record-holder Ann Bates of Canada. In 1879, Bate's newborn weighed in at a whopping 23 pounds, 12 ounces.