Recognizing the unique prenatal phenotype of <scp>Prader‐Willi</scp> Syndrome ( <scp>PWS</scp> ) indicates the need for a diagnostic methylation test

OBJECTIVES Prader-Willi syndrome (PWS) is a neurogenetic disorder characterized by mental retardation, morbid obesity, and endocrine and behavior disorders. We previously showed in a small group of patients that PWS may have a unique prenatal phenotype. We aimed to characterize clinical and ultrasonic features in a larger series of pregnancies with a PWS fetus. METHODS We retrospectively interviewed all mothers of children with PWS followed in the Israel national multidisciplinary PWS clinic. We compared details of the PWS pregnancy with the pregnancies of healthy siblings and with data from the general population. Medical records including ultrasound reports, obstetric records, and genetic results were analyzed. RESULTS Distinct prenatal features of PWS pregnancies included abnormal fetal growth [fetal growth restriction (FGR) (37.3%), increased head to abdominal circumference ratio (44.8%), decreased abdominal circumference (49.2%)], markedly decreased fetal movements (DFM) (80.4%), and polyhydramnios (42.0%) (P