A fetal resonance scan was a procedure done by a physician to determine the health of an unborn child.
In 2378, Lieutenant B'Elanna Torres walked into sickbay on the USS Voyager, where an away team consisting of Lieutenant Joseph Carey, Ensign Harry Kim, Neelix and Commander Chakotay were receiving innoculations in preparation for their mission to Uxal, which had a posionous atmosphere. The Doctor thought Torres was in early for her fetal resonance scan, where in fact, she wanted to join the away team. However, her husband, Tom Paris, talked her out of going, for concern of the health of their unborn child. (VOY: "Friendship One")