Sirenomelia in uneventful pregnancy.

A rare case of sirenomelia at 38 weeks of gestation is reported. Fusion of the lower extremities and incomplete development of the bony pelvis was associated with agenesis of the urinary and genital systems, anorectal atresia and a single large umbilical artery. There was complete situs inversus of the single lower limb. This was composed of two partially fused femurs, a common tibia without fibula, and a rudimentary foot having three metatarsal bones and their corresponding toes. The present case was also interesting for its association with hypoplasia of the lungs. The pathogenesis of sirenomelia is discussed.