Abstract
Trisomy 12 is a rare chromosomal abnormality characterized by the presence of an extra copy of chromosome 12 in some or all cells. This condition can present with a variety of phenotypic manifestations, depending on the extent of mosaicism and the specific genes involved. Prenatal diagnosis of trisomy 12 is challenging due to its variable presentation and potential overlap with other chromosomal abnormalities. This case report describes a 23-year-old woman referred to a Maternal-Fetal Medicine (MFM) clinic following abnormal findings on a routine prenatal ultrasound at 20 weeks' gestation. The ultrasound indicated increased nuchal fold, a pleural effusion, clenched hands, shortened long bones, flat facial features, and clubbed feet. Amniocentesis showed a partial trisomy of distal 12q on the cytogenetic band 12q21.2 to 12q24.33. The patient was advised on the need for close monitoring of fetal growth and development through serial ultrasounds and follow-up visits, with a multidisciplinary approach including genetic counseling. This case underscores the importance of comprehensive prenatal ultrasound screening, prenatal genetic diagnosis, and multidisciplinary management in addressing the varied phenotypic manifestations of trisomy 12.