His mother, Cynthia Sigler of Vista, said that her immediate reaction was: "How'd he fit?"
Doctors initially estimated that Jayden would weigh about 9 pounds, but that number jumped to 11 by early March, the mother told the newspaper.
Dr. Jerald White, who delivered the baby at Tri-City Medical Center, said Jayden was the biggest of the 20,000 newborns he has helped usher into the world since he started in 1961.
The doctor said delivering a very large baby via cesarean section is more challenging, but "it wasn't so difficult that it created a problem for anybody."
Sigler said her own family didn't believe her at first — she convinced her cousin it wasn't a joke only after showing a photo of the scale readout.
Jayden's birth weight is almost twice that of his sister, Jailyn, now 2½. She was 7 pounds, 2 ounces at birth.
Sigler said she'll have to exchange all the baby clothes she bought for larger sizes.
A hospital official was unable to immediately determine Friday whether Jayden was the largest baby ever delivered there. It was also not clear where the newborn ranks among the largest babies also born in San Diego County.