Sirenomelia With Complete Caudal Regression in a Preterm Infant Born to a Mother With Poorly Controlled Type 1 Diabetes Mellitus: A Case Report on Clinical Presentation and Perinatal Management Challenges.

Sirenomelia is a rare, lethal congenital anomaly characterized by caudal regression and lower limb fusion. The etiopathogenesis is multifactorial, with maternal glycemic dysregulation established as a significant risk factor, contributing to the development of this severe malformation syndrome. We report an infant born at 33 weeks' gestation with a birth weight of 1,900 g to a 36-year-old multiparous woman with poorly controlled type 1 diabetes mellitus (HbA1c, 9.8%). Prenatal ultrasound evaluation during the second trimester identified significant fetal abnormalities consistent with a lethal congenital malformation syndrome. The neonate presented with complete lower limb fusion, bilateral renal agenesis, imperforate anus, ambiguous genitalia, and dysmorphic facial features. Despite supportive palliative care, the infant died at 24 hours of life due to complications of bilateral renal agenesis and associated malformations. This case emphasizes the critical importance of optimal preconception glycemic control in diabetic women and highlights the challenges in prenatal counseling and neonatal management of sirenomelia. The case contributes to the growing evidence linking poor maternal glycemic control with severe caudal regression anomalies and underscores the need for enhanced periconceptional counseling.