Hidden in Plain Sight: A Rare 7q Deletion Masquerading as a Common Aneuploidy on Prenatal Ultrasound.

Prenatal diagnosis of rare chromosomal microdeletions is challenging when fetal abnormalities mimic common aneuploidies. Traditional karyotyping may miss submicroscopic aberrations detectable by chromosomal microarray analysis (CMA). We report a case of 7q31.1-q32.3 microdeletion syndrome identified through CMA, highlighting its diagnostic value. A 28-year-old primigravida at 29 weeks presented with polyhydramnios, fetal growth restriction, short nasal bone, and cardiac abnormalities suggestive of trisomy. CMA revealed a 21.58-megabase deletion at 7q31.1-q32.3. She delivered at 37 weeks by cesarean section. The neonate developed respiratory distress requiring intensive care and was found to have an atrial septal defect, patent ductus arteriosus, pulmonary artery stenosis, ventriculomegaly, and feeding difficulties. This case demonstrates that prenatal ultrasound features suggestive of common aneuploidies may instead arise from other, less common genetic abnormalities. CMA offers superior diagnostic precision and should be considered in atypical prenatal presentations resembling aneuploidy.