Abstract
Objective: Tetrasomy 9p and trisomy 9p are rare chromosomal aberrations. The phenotypes of tetrasomy 9p and trisomy 9p are variable. Most cases are diagnosed in the postnatal period. The study aims to analyze the prenatal phenotype of tetrasomy 9p and trisomy 9p in terms of ultrasound and screening tests. Methods: A set of 1573 prenatal tests performed from 2016 to 2021 was reviewed to identify all cases with trisomy 9p and tetrasomy 9p. In four cases with 9p gain, non-invasive and invasive test results were analyzed. Results: Four cases with the 9p gain were diagnosed in the prenatal period: two cases with tetrasomy 9p and two cases with trisomy 9p. Nasal bone hypoplasia and ventriculomegaly are common features of 9p gain. In two out of four cases with the 9p gain, an increased risk of trisomy 21 was found in the combined first-trimester screening test. Conclusion: Trisomy 9p and tetrasomy 9p are characterized by a variable phenotype in the prenatal period, manifesting in genetically abnormal fetuses. The tetrasomy 9p and trisomy 9p may suggest trisomy 21 in the first trimester.