This is one cool baby.

A photo posted to Reddit last week by soon-to-be father Brandon Hopkins appears to show his child giving a thumbs-up sign in utero.

"Recent ultrasound results look good," Hopkins, 31, of Meadville, Pennsylvania, wrote in the Reddit post that's now gone viral.

Hopkins and his wife don't know the sex of the child yet. But they know they are expecting twins in January.

"I thought it was really cool," Hopkins told ABC News of the shot.

Social media users have been quick to name the baby "Fonzie fetus," in homage to the laid back "Happy Days" character.