Abstract
Background: Fetal growth restriction (FGR) is a significant obstetric complication associated with increased perinatal morbidity and long-term developmental risks. Despite advances in prenatal diagnosis, the genetic etiology of isolated FGR remains incompletely characterized, complicating genetic counseling and clinical management. Objective: This study aimed to systematically evaluate the genetic causes of isolated FGR by integrating karyotyping, chromosomal microarray analysis (CMA), and trio-based whole exome sequencing (trio-WES) and to assess the incremental diagnostic yield of this sequential approach. Methods: A retrospective cohort of 153 fetuses with isolated FGR (diagnosed by ultrasound between February 2018 and July 2024) underwent karyotyping and CMA. Cases with normal results from both tests (n = 50) were subsequently analyzed by trio-WES. Results: Karyotyping identified chromosomal abnormalities in three cases (2.0%). CMA detected pathogenic/likely pathogenic copy number variations (CNVs) or uniparental disomy (UPD) in twelve cases (7.8%), including the three karyotypic abnormalities and nine additional cases (5.9% incremental yield). Trio-WES performed on 50 CMA-negative cases identified pathogenic or likely pathogenic variants in 12 cases (24%). Among these, seven cases (14% of the WES subgroup) harbored variants directly causative of FGR, including one case of UPD(6) missed by CMA alone. Additionally, trio-WES revealed seven incidental pathogenic/likely pathogenic variants not directly linked to FGR and identified one case in which FGR was attributed to maternal hyperphenylalaninemia. Conclusions: The sequential application of CMA and trio-WES significantly improves the diagnostic yield for isolated FGR. Trio-WES proved particularly valuable in detecting UPD and single-gene variants missed by CMA alone and in revealing contributory maternal genetic conditions. These findings support the integration of advanced genetic testing into the diagnostic workup for isolated FGR to enhance etiological diagnosis, facilitate comprehensive genetic counseling, and inform multidisciplinary management.