The fetal external ear.

The ridge pattern of the external ear was evaluated in 50 normal subjects during the second half of pregnancy. Definition was found to progress with gestational age, with a fully defined pattern implying maturity beyond 33 weeks. The external ear was edematous in patients with severe fetal hydrops. Anomalous shape or unusual prominence of the ear was observed antenatally in 4 cases of lethal dwarfism.