EP07.23: A rare case of fetal sirenomelia malformation in the second trimester with its ultrasound appearance and review of the literature

Sirenomelia, an exceptionally rare congenital anomaly, epitomises the most severe manifestation of fetal caudal agenesis, characterised by partial or complete fusion of the lower limbs. Typically, this condition is accompanied by profound abnormalities in the urinary and digestive systems, including renal absence, potentially leading to fatal outcomes. Our objective was to diagnose this malformation as early as possible during pregnancy, aiming to distinguish it from caudal regression syndrome and meticulously monitor associated obstetric complications. We present a case of sirenomelia diagnosed in the second trimester at 20 weeks of gestation. The patient had no notable medical, toxicological, or psychological history, and consanguinity was absent. Ultrasound examination revealed a progressively developing single-fetal pregnancy. The fetus exhibited sirenomelia, ventricular septal defect with aorta originating on the septum, small hyperechoic kidneys, and severe oligohydramnios. In our discussion, we address the criteria for ultrasound diagnosis of sirenomelia and explore potential malformative associations. In conclusion, sirenomelia represents a severe congenital anomaly incompatible with extrauterine life. Timely diagnosis, ideally during the second trimester ultrasound examination, is imperative. Early recognition of this condition facilitates appropriate management and counselling for affected pregnancies.