North Shore University Hospital says the event only happens in one of every 200 million births.
Dr. Victor Klein, who delivered the boys, says many triplets are considered to be identical but if they are born naturally, no one really knows for sure.
But it's more certain in this case because Allison Penn received in vitro fertilization. Doctors know the boys were born from one embryo that split twice and from one placenta, the organ that nourishes the babies.
