First-trimester ultrasound diagnosis of sirenomelia: A case report.

Sirenomelia is a rare congenital malformation characterized by the fusion of the lower limbs and is generally associated with severe multisystem anomalies. Advances in prenatal imaging have significantly improved the ability to diagnose this condition early in pregnancy, allowing for timely counseling and management. We report the case of a 37-year-old woman who was referred at 13 weeks of gestation for first-trimester combined screening. Ultrasound revealed a single viable fetus with hallmark features of sirenomelia. The diagnosis was confirmed on postmortem after termination of pregnancy at 16 weeks of gestation. Postmortem radiographic imaging and genetic analysis ruled out chromosomal abnormalities, supporting a sporadic etiology. This case highlights the value of antenatal ultrasonography, which has high sensitivity for the diagnosis of sirenomelia, a rare condition with a poor prognosis. Earlier diagnosis allows for proactive, patient-centred counseling and management.