Whenever you call him ‘Nash potato’, or you cheer him on when he’s trying to pull himself up, he just hams it up,” he said. “It makes him want to succeed and do more.”

Although most studies measuring premature-baby outcomes start at 22 and 23 weeks — reporting U.S. survival rates between 10 and 20 percent at that gestation — University of Iowa Health Care is among the few hospital systems that take on babies at 21 weeks.