Prader-Willi syndrome: is there a recognizable fetal phenotype?

Objectives: To determine fetal features, which could lead to the diagnosis of Prader-Willi syndrome (PWS) during pregnancy.

Methods: We analyze the ultrasound features, genetic studies and pathologic findings in two cases of PWS diagnosed during pregnancy.

Results: In the first case, diminished fetal movement, polyhydramnios and oddly positioned hands and feet suggested PWS. Methylation studies confirmed diagnosis and a deletion was detected in the 15q11-q13 region. In the second case, similar ultrasound findings led to prenatal diagnosis of PWS with an abnormal methylation pattern compatible with uniparental disomy. Both fetuses had a characteristic appearance at 28 and 30 weeks' gestation, which included a peculiar position of hands with flexed wrists and dorsi-extended feet with flexed toes.

Conclusions: The peculiar position of the extremities combined with diminished fetal movement and polyhydramnios seems to be characteristic and should suggest PWS.