Prenatal sonographic predictors of maternal mirror syndrome in hydropic fetuses

Mirror syndrome is a rare life-threatening condition in which a pregnant individual develops hypertension, visceral and pulmonary edema, "mirroring" the fluid overload of their hydropic fetus. Data is limited to less than 120 cases of mirror syndrome described in the literature.

We sought to determine if a cardiogenic versus noncardiogenic etiology for hydrops fetalis was associated with mirror syndrome. We also examined whether there are sonographic predictors for progression from hydrops to mirror syndrome.

This is a retrospective cohort study of all singleton pregnancies evaluated at our fetal center from 2012 to 2023 with a prenatal diagnosis of hydrops fetalis, including both immune and nonimmune etiologies. Participant history, pregnancy outcome, and ultrasound data were obtained. Cases were classified as having mirror syndrome if they presented with fetal hydrops, new or worsening hypertension and significant maternal edema. Participants were further classified by the fetal condition causing hydrops, either cardiogenic or noncardiogenic. A cardiogenic etiology was defined as the presence of high cardiac output heart failure or other evidence of fetal cardiac compromise. Bivariate analyses were performed comparing those with and without mirror syndrome, and logistic regression was used to evaluate etiology of hydrops as well as the predictive value of affected fetal fluid compartments and placental thickness with mirror syndrome.

Among 182 cases of hydrops, mirror syndrome was diagnosed in 29/182 (16%). Hydrops due to a cardiogenic etiology was more common in mirror syndrome, 18/29 (62%) compared to 56/153 (37%) without, P=.01. A cardiogenic etiology for hydrops (OR, 2.83; 95% CI, 1.27-6.61) and placental thickening (OR, 7.20; 95% CI, 2.54-20.6) were significantly associated with mirror syndrome.

Cardiogenic hydrops was significantly associated with progression to mirror syndrome, suggesting a potential common pathophysiology between fetal cardiovascular compromise and mirror syndrome. Fluid collection within the placenta (thickening) was also significantly associated with mirror syndrome.