RESUMO
Sirenomelia, also known as mermaid syndrome, is a rare congenital anomaly characterized by a single lower extremity which is associated with abnormalities in other organ systems, commonly affecting the gastrointestinal and the urogenital systems. It is sporadic with no increased risk in subsequent pregnancies. In almost all the cases of sirenomelia, a single umbilical artery (SUA) is present which arises from the abdominal aorta. The exact etiology of sirenomelia is unknown. Sirenomelia can be confidently diagnosed in the 1st trimester while the diagnosis in the 2nd and 3rd trimesters is difficult due to the lack of amniotic fluid in the later gestation. Antenatal diagnosis of this universally lethal condition is desirable so that possible termination of pregnancy can be offered at the earliest.