OBJECTIVE: To define fetal ultrasound characteristics triggering an antenatal diagnosis of Prader Willi syndrome (PWS).
METHODS: Retrospective analysis of sonographic characteristics retrieved from obstetric ultrasound records. All children (n=11) had a postnatal genetically confirmed diagnosis of PWS.
RESULTS: All patients (n=11) showed at least one aspecific abnormality on prenatal ultrasound. Ten out of eleven (90.9 %) had decreased fetal movements, 7 (63.6%) presented in breech position, 7 (63.6%) had severe intra-uterine growth restriction (<5th centile) and 4 (36.4%) showed a polyhydramnios. Immobile flexed limbs and clenched hands were seen in one patient (9.1%). Severe growth restriction combined with polyhydramnios favors the diagnosis in 3/11 cases.
CONCLUSION: Prenatal sonographic phenotype of PWS includes decreased fetal movements, fetal malpresentation, severe intra-uterine growth restriction and polyhydramnios. These findings are not specific to PWS, but the combination of some of them (especially severe intra-uterine growth restriction and polyhydramnios) can prompt clinicians to perform invasive testing leading to a molecular cytogenomic diagnosis prenatally.