Mirror Syndrome (Ballantyne Syndrome): Prenatal Diagnosis, Pathophysiology, and the Role of Fetal Therapy—A Narrative Review

Mirror syndrome is a rare maternal–fetal condition associated with fetal hydrops and a high risk of adverse maternal and fetal perinatal outcomes. Its diagnosis is challenging due to the lack of standardized diagnostic criteria and its clinical and biochemical overlap with preeclampsia. This narrative review summarizes current evidence on mirror syndrome, with a focus on prenatal diagnosis, placental pathophysiology and the role of targeted fetal therapy. Mirror syndrome is most frequently associated with non‐immune causes of fetal hydrops and available evidence supports a central role for the placenta in disease pathogenesis. Recent data suggest that angiogenic biomarkers, including sFlt‐1 and PlGF, may be useful in the differential diagnosis from preeclampsia. Resolution of fetal hydrops through in utero therapy can lead to rapid maternal improvement and pregnancy prolongation in selected cases. Early recognition and multidisciplinary management are essential to optimize maternal and fetal outcomes.