Sirenomelia is a congenital structural anomaly characterized by abnormal development of the caudal region of the body. The peculiar characteristics of sirenomelia are complete fusion of bilateral lower limbs giving the fetus an appearance of mermaid. The other anatomical defects may be renal agenesis, gastrointestinal defects, and absent external genitalia. The outcome of the condition is usually fatal for the baby despite attempts for corrective surgery. This abnormality was initially confused with caudal regression syndrome, but later was given a new name, i.e., sirenomelia mermaid syndrome.

We present a case of a 23-year-old primigravida unbooked case reported at 25 weeks 6 days period of gestation with complaint of decreased fetal movements. The ultrasound was suggestive of single live intrauterine fetus of 24 weeks with severe oligohydramnios (amniotic fluid index 1–2 cm). Based on fetal magnetic resonance imaging, which revealed multiple congenital anomalies including nonvisualization of kidneys and poorly formed lower limbs, provisional diagnosis of sirenomelia with renal aplasia incompatible with life was made. She delivered a baby 943 gm with features and appearance suggestive of mermaid syndrome (sirenomelia). Patient was discharged with advice to report early in next pregnancy.

Sirenomelia is a very rare disorder, with prevalence of 1 in 100,000 live births with a total of 300 cases reported until today in which 9 are from India. The precise etiology of sirenomelia is not well understood. Many theories have been proposed, but none of these is considered definitive. It is very important to diagnose this universally fatal condition by ultrasonography in early pregnancy, so that termination of pregnancy can be carried out.

Verma P, Bhardwaj D, Sinha SK, Heer AK. Sirenomelia: A Rare Congenital Anomaly. J South Asian Feder Obst Gynae 2017;9(3):271-273.