A fetus with Prader-Willi syndrome showing normal diurnal rhythm and abnormal ultradian rhythm on heart rate monitoring.

Clinical features of Prader-Willi syndrome in neonates are marked hypotonia with the absence of crying and feeding difficulty so that prenatal diagnosis of Prader-Willi syndrome is strongly hoped in order to provide appropriate medical and psychological care for neonates and their families. However, the clinical picture of Prader-Willi syndrome in utero has not been well described. We report a pregnancy associated with Prader-Willi syndrome manifesting polyhydramnios, large biparietal diameter of the fetus and characteristic fetal heart rate pattern: prolonged inactive periods and diurnal variation of the incidence of heart rate accelerations. These findings may offer a clue to the prenatal diagnosis of Prader-Willi syndrome, although molecular cytogenetics is mandatory for the definite diagnosis.