Mirror syndrome which is also known as Ballantyne's syndrome is a pregnancy complication which combines two conditions: fetal hydrops and maternal preeclampsia. Hydrops is the accumulation of fluid in two of more cavities (lungs, heart, skion, abdomen). It is called mirror syndrome because it mirrors the edema or accumulation of fluid in the fetus with the edema in the mother, the edema observed in the fetus and edema in the mother with preeclampsia are similar.

Making the diagnosis of mirror syndrome is important because the diagnosis of mirror syndrome is often associated with increased fetal and maternal risks.

The incidence of mirror syndrome in pregnancy is low and few cases have been published. A review in the literature of 56 reported cases of mirror syndrome showed the following findings of association with these conditions:

• rhesus isoimmunization (29%),
• twin-twin transfusion syndrome (18%),
• viral infection (16%) and
• fetal malformations, fetal or placental tumors (37.5%)

The gestational age at diagnosis of mirror syndrome was between 22 to 27 weeks of gestation. Edema (80-100%) and hypertension (57-78%) were most often observed followed by  proteinuria (20-56%). The overall rate of intrauterine death was 56%. Severe maternal complications including pulmonary edema occurred in 21.4%. Maternal symptoms disappeared 4.8-13.5 days after delivery.

The authors concluded that mirror syndrome was associated with a substantial increase in fetal mortality and maternal morbidity.