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

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

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

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.

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