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Chromosomal microarray (CMA) is recommended as a first tier investigation for patients with developmental delay (DD), intellectual disability (ID), autistic spectrum disorder (ASD), and multiple congenital anomalies (MCA). It is widely used in the prenatal and postnatal settings for detection of chromosomal aberrations. This is a retrospective review of all array comparative genomic hybridization (aCGH/ array CGH) findings ascertained in two major prenatal and postnatal genetic diagnostic centers in Hong Kong from June 2012 to December 2017. Medical records were reviewed for cases with pathogenic and variants of uncertain clinical significance (VUS). Classification of copy number variants (CNVs) was based on current knowledge and experience by August 2018. The aims of this review are to study the diagnostic yield of array CGH application in prenatal and postnatal settings in Hong Kong and to describe the spectrum of abnormalities found. Prenatal indications included abnormal ultrasound findings, positive Down syndrome screening, abnormal noninvasive prenatal test results, advanced maternal age and family history of chromosomal or genetic abnormalities. Postnatal indications included unexplained DD, ID, ASD, and MCA. A total of 1,261 prenatal subjects and 3,096 postnatal patients were reviewed. The prenatal diagnostic yield of pathogenic CNV and VUS (excluding those detectable by karyotype) was 3.5%. The postnatal diagnostic yield of pathogenic CNV was 15.2%. The detection rates for well-defined microdeletion and microduplication syndromes were 4.6% in prenatal and 6.1% (1 in 16 index patients) in postnatal cases, respectively. Chromosomes 15, 16, and 22 accounted for over 21 and 25% of pathogenic CNVs detected in prenatal and postnatal cohorts, respectively. This review provides the first large scale overview of genomic imbalance of mostly Chinese patients in prenatal and postnatal settings., (© 2019 Wiley Periodicals, Inc.)