BACKGROUND: This study conducted genetic analysis on fetuses indicated to be at high risk by non-invasive prenatal testing (NIPT) to explore the etiology. METHODS: Karyotype analysis and single nucleotide polymorphism array (SNP-array) were performed to detect copy number variations in fetal amniotic fluid and parental peripheral blood. RESULTS: Fetal karyotype showed 46, X?, del (4) (q28q31.2). SNP-array revealed a novel 22.3 Mb deletion in the 4q28.1q31.21 segment. No abnormalities were found in the karyotype and SNP-array of the fetal parents. After induction of labor, the fetus was diagnosed with fetal growth restriction (FGR)
being small for its gestational age by three weeks. CONCLUSIONS: Using G-banding karyotype analysis and SNP-array, a prenatal diagnosis of a fetus with rare 4q28.1q31.21 microdeletion was made. The 4q28.1q31.21 microdeletion was identified as the cause of fetal FGR, leading to accurate genetic counseling for pregnant women.