Clinical characteristics and risk factors of mirror syndrome: a retrospective case-control study

Mirror syndrome (MS) is a rare obstetric disorder complicated with high maternal morbidity and fetal mortality. MS is often misdiagnosed or underdiagnosed due to the low incidence and lack of awareness of its diverse features. This study aimed to summarise the etiology, clinical characteristics, and risk factors of MS among mothers with fetal hydrops. This retrospective case-control study included 37 pregnant women with fetal hydrops in the second and third trimesters from 58,428 deliveries performed at the Third Affiliated Hospital of Sun Yat-Sen University between January 2012 and December 2020. Cases were categorized as MS and non-MS according to the presence or absence of maternal mirroring symptoms. Binary logistic regression was performed for analysis. Fourteen women developed MS with an overall incidence of 0.024% (14/58,428) and 37.8% (14/37) in the fetal hydrops cases. Among the 11 MS cases with known associated etiologies, seven had alpha thalassemia major. Onset of fetal hydrops was later (27.8 vs. 23.0 weeks) and the rate of placental thickening was higher (85.7% vs. 34.8%) in the MS group than in the non-MS group (P