Doctors told Ian and Brittani McIntire, of Hutchinson, Kansas, they don't think boy, already named Mason, will survive because he has a hole in his heart and an abnormal brain.
"His only chance of survival would be heart surgery but they wouldn't do heart surgery on him because of his brain," Brittani told CBS affiliate KWCH.
The family is nonetheless heartened by the sonogram image.
"We know we have a piece of them together that will last forever and it's special to have," said Brittani, who has two other children with her husband.
If the fetus survives, doctors will deliver him and his twin C-section. But if he doesn't, the family said they are comforted to know his sister, who they've named Madilyn, is with him.
"She's the only one who can actually be there and holding onto him through it," Brittani said. "So it's comforting to know that if he does pass, he won't be alone."