Situs Inversus Totalis First Detected in the Third Trimester: Diagnostic Pitfalls in Routine Fetal Ultrasonography – A Case Report

Introduction: Situs inversus is a rare congenital condition characterized by a mirror-image reversal of thoracic and/or abdominal organs, with an estimated incidence of 1 in 10,000 live births. Although many individuals are asymptomatic, the condition is associated with congenital heart disease (CHD), and because a mirror-image heart may appear structurally normal, it can be overlooked at routine prenatal ultrasonography unless fetal laterality is determined first. Case Description: A 25-year-old primigravida was referred at 34– 35 weeks of gestation for evaluation of fetal growth restriction; fetal situs inversus had not been identified at previous antenatal examinations. Ultrasonography showed the stomach on the right, the liver on the left, the descending aorta to the right of the spine and the inferior vena cava to the left, with the cardiac apex directed to the right. Fetal echocardiography confirmed atrial situs inversus with mirror-image dextrocardia and normal systemic and pulmonary venous return, without structural cardiac defects or features of heterotaxy. Doppler indices were normal, and the fetus was categorized as small for gestational age. The patient delivered a neonate weighing 2365 grams vaginally at 39 weeks and 4 days, and postnatal echocardiography confirmed mirror-image dextrocardia with normal intracardiac anatomy. Conclusion: Isolated situs inversus totalis can remain undetected until the third trimester because each standard view of a mirror-image heart appears normal. Determining fetal laterality at the start of every obstetric scan, followed by detailed fetal echocardiography to exclude CHD and heterotaxy, consideration of genetic evaluation, and postnatal follow-up for primary ciliary dyskinesia, allows accurate counseling and appropriate perinatal planning.