Background: Prader–Willi syndrome (PWS) is a multisystemic complex imprinting disorder. Prenatal diagnosis of PWS is still a challenge with non-specific ultrasound markers and limitations for diagnosis with non-invasive screening methods. Prenatal suspicion and early postnatal diagnosis are essential for promoting healthy growth and development, preventing complications, and providing healthcare professionals and families with the necessary support and resources for effective management. Presentation: We report two PWS cases caused by maternal uniparental disomy, who presented with IUGR, characterized by reduced fetal abdominal circumference (AC) in the second and early third trimesters, reduced fetal movements, normal Doppler indices and oligohydramnios. They were diagnosed in the early neonatal period with no prenatal suspicion but with similar ultrasound markers of the developing pregnancies, analyzed retrospectively. Aim: This study aims to emphasize the need to raise awareness among specialists about genetic syndromes such as Prader–Willi syndrome, to improve the information provided to couples regarding the limitations of current prenatal screening methods, as well as to ensure that, in cases of prenatal suspicion, appropriate genetic testing can be initiated. A confirmed diagnosis would allow timely and adequate measures to be taken, given the complications of the postnatal period in these patients and their need for specialized care and management. Conclusions: The presence of the aforementioned prenatal characteristics may raise suspicion for PWS. In such cases, invasive diagnostic procedures and methylation testing may be indicated, enabling earlier diagnosis and timely management, which can ultimately improve the quality of life of affected individuals and their families.