Ian and Brittani McIntire, from Hutchinson, Kansas, had been delighted to discover they were going to have two new additions to the family after Brittani fell pregnant with twins.
But their joy soon turned to sorrow after the learned that one of their babies was not going to survive, Pix 11 reports.
During their six week sonogram, the McIntre's learned that their twin boy Mason had a hole in his heart and an abnormal brain.
At just nine ounces, he weighed less a third than his sister Madilyn who at 2lbs was growing at a healthier rate.
Tiny Mason had his hand grasped tightly in his sister's.
The moving picture is a comfort to the baby's parents who may never get to meet him.
"Most twins when she's trying to take pictures and stuff they're kicking each other and hitting each other and she said without twins it seems like she was very protective over him," Ms McIntire said.
"I know I'm holding him, I'm carrying him but... she's the only one who can actually be there and is holding onto him... so it's comforting to know that if he does pass, he won't be alone."
Doctors told the couple that their son's only chance of survival would be to carry out heart surgery.
But they say they won't risk the surgery as the growing baby also had brain abnormalities, Ms McIntire said.
With medics unable to intervene to help Mason, Ms McIntire has a long and anxious wait before she will learn if she gets the chance to meet her son.
Both twins are due in September but the couple have been warned there is a likely possibility Mason could die in the womb before the date.
Mr McIntire said that whatever happened, the black and white sonogram would always be a special reminder of their babies.