(CBS News) Jade Packer and Ryan King are the proud parents of one big baby boy.
Baby George King was born on February 11, reports the BBC, weighing a whopping 15 lbs and 7 ounces. He's more than twice the size of an average baby, and wears clothes made for 3 to 6-month-olds as a newborn.
Doctors and her new parents weren't expecting their new son to be quite that size. Big babies did not run in either Packer or King's families.
"When his head was out that's when they realized he was so big," Packer explained to the BBC.
Large babies are known as macrosomia in the medical community. In order to be classified as a oversized infant, babies need to be in the top 10th percentile in weight when they were born, normally meaning between 9 to 10 pounds.
It might be hard to believe that doctors weren't able to tell that George was going to be larger than average while in utero, but Dr. Jennifer Wu, OBGYN at Lenox Hill Hospital in NY, explained to CBSNews.com that it is often hard to predict the size of a baby.
"Ultrasound is not 100 percent," she said. "It's about 10 percent off, and it actually is more off if the baby is extremely small or extremely large."
Wu, who has no involvement in this case, said that doctors estimate the size of a child by taking measurements of the head, belly and femur bone in their leg. Sometimes measurements can be hard to get if you do a sonogram later in the pregnancy, because the head is low in the pelvis or birth canal. Other times, babies might be might not be proportional in size, changing the estimate.
"Sometimes you have a baby whose head is disproportionally bigger, and it's got a good sized head but a skinny body," she explained. "It could be a pound or a pound and a half less than estimated."
A mother who is overweight or obese, who gains weight excessively during pregnancy or has gestational diabetes is at a higher risk of having a large baby. Even if doctors know the child is going to be big, they can't necessarily deliver the child earlier. For children whose mothers have gestational diabetes, their lungs tend not to develop at the same rate as their body.
"If the lungs are not mature and you deliver the baby too early, the baby might have to be in the NICU (neonatal intensive care unit) and need assistance while breathing," Wu said.
Other issues with large baby births include difficult vaginal delivery, more soft tissue trauma and larger tears during pregnancy, Wu explained. The mother and child are also at an increased risk of shoulder dysplasia, something that Packer reportedly experienced with George's birth.
During shoulder dysplasia, the baby's head comes out, but their shoulder gets stuck on the mother's pelvis. The umbilical chord is compressed and cuts off the baby's access to oxygen. In George's case, he went without oxygen for 5 minutes, which means that he is at risk for brain damage. He was given a 10 percent chance of survival.
"To be told that you're going to lose your baby after those nine months of waiting to finally meet him is the worse," King told the BBC.
George was held in the hospital for 4.5 weeks for observation, and now is going for regular check-ups. An MRI scan revealed that he would not have any major problems from the lack of oxygen, but he may have some learning disabilities, Packer explained.
But, George won't stay his giant size for that long. Since he's been home, he's only gained one pound, and probably won't be larger than average forever.
"He's a little miracle -- well, big miracle really," she said laughing.
Michelle Castillo, CBS News