Prader Willi syndrome (PWS) is a complex multisystemic disorder caused by the absence or loss of function of a group of genes located in the proximal region of the long arm of chromosome 15 of paternal origin. The Prader-Willi syndrome (PWS) is characterized by diminished fetal activity, obesity, muscular hypotonia, mental retardation, short stature, hypogonadotropic hypogonadism Prenatal diagnosis of PWS, which is important in order to provide appropriate genetic counselling, still remains difficult due to the lack of specificity of the findings above described. We report a case of PWS with the following ultrasound prenatal findings: polyhydramnios, mild prenatal growth restriction, diminished fetal movements (spontaneous and provoked), cryptorchidism and retrognathia,three dimensional ultrasound (3D) allowed us to evaluate facial anomalies, Neonatal physical examination revealed the symptoms already observed prenatally as well as a marked hypotonia which led to the suspicion of Prader Willi Syndrome, which was confirmed by genetic testing, deletion of 15q11-q13 in the paternally inherited chromosome. Ultrasound can provide important information in the suspicion of a syndrome. In this case, we are able to show some sonographic features as cryptorchidism and the suspected facial dismorphy in 2D and 3D, suggestive of a syndromic fetus. In the 3D midsagittal plane we observed retrognathia and prominent upper lip, also evident in the coronal plane (3D multiplanar representation). These images are correlated with the neonate's face photos. PWS diagnosis should be considered in cases of polyhidramnios, fetal hipokinesia and other inespecific sonographic findings. In the suspicion of facial anomalies, we should consider the evaluation of the fetal face morphology and its assessment with 3D/4D.

Enlarged fetal nuchal translucency (NT) is a well established ultrasonographic marker for aneuploidy screening, especially during the first trimester of gestation. Changes in the ductus venous (DV) blood flow velocity waveform in the first and second trimester have been reported in some chromosomally abnormal fetuses with enlarged NT. The aim of this study was to evaluate the role of NT thickness and DV blood flow assessment at 10–16 weeks' gestation in screening for chromosomal abnormalities in multiple pregnancies. Nuchal translucency thickness was measured and ductus venosus blood flow (pulsatility index) was prospectively evaluated in 318 multiple pregnancies between 10 and 16 weeks of gestation referred to our unit for prenatal care and delivery. All cases were screened for chromosomal defects combining maternal age and fetal NT thickness. There were 283 twins, 34 triplets, 1 cuadruplet pregnancy. Chromosomal abnormalities were found in 15 cases (2.4%). Using NT and DV greater than 95th centile as a cut-off, the overall detection rate was 73.3% and 81.8% with a specificity of 95.9% and 92.3%. The detection rate for trisomies 21, 18, 13 was 88.9% and 75% with a specificity of 95.4% and 91.8%. When NT and DV were done between 10–13 weeks' gestation the detection rate was 77.8% and 85.7% with a specificity of 95.5% and 92.1%. Between 14–16 weeks' gestation the detection rate was 66.7% and 75% with a specificity of 96.8% and 93%. The detection rate for pregnancies in women under 35 years of age was 85.7% and 71.4% with a specificity of 95.8% and 93.2%. For pregnant women above 34 years was 62.5% and 100% with a specificity of 96.1% and 90.9%. Our results suggest that the evaluation of NT thickness and DV blood flow assessment at 10–16 weeks' gestation is a useful tool in the screening for a chromosomal defects in multiple pregnancies.