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Background: To analyze population‐based trends in the prenatal diagnosis of sex chromosome aneuploidy (SCA) since the availability of non‐invasive prenatal testing (NIPT). Methods: Retrospective state‐wide data for all prenatal diagnoses performed <25 weeks gestation from 2005 to 2020 in Victoria, Australia. Non‐invasive prenatal testing became locally available from 2012. The prenatal diagnosis rates of SCA as proportions of all prenatal diagnostic tests and all births were calculated. Statistical significance was assessed with the χ2 test for trend, with p < 0.05 considered significant. Results: 46,518 amniocentesis and chorionic villus sampling were performed during the study period, detecting 617 SCAs. There was a significant increase in the rate of prenatal SCAs from 5.8 per 10,000 births in 2005 to 8.7 per 10,000 births in 2020 (p < 0.0001). This increase was predominantly due to 47,XXY cases, 91% of which were ascertained via positive NIPT for this condition in 2020. The prenatal diagnosis rate of 47,XXY significantly increased from 0.8 per 10,000 births in 2005 to 4.3 per 10,000 births in 2020 (p < 0.0001). Conclusion: Screening for SCAs using NIPT has directly led to an increase in their prenatal diagnosis on a population‐wide basis, especially 47,XXY. This has implications for clinician education, genetic counselling, and pediatric services. Key points: What is already known about this topic? Noninvasive prenatal testing for fetal aneuploidy has created new opportunities for the identification of sex chromosome conditions without an ultrasound phenotype. What does this study add? This is the first population‐based data demonstrating the significant rise in prenatal diagnosis of sex chromosome conditions on amniocentesis and chorionic villus sampling, predominantly driven by increases in the prenatal diagnosis of 47,XXY.The prenatal diagnosis rate of 47,XXY has increased from one in 12,500 births to one in 2300.This five‐fold increase in the prenatal diagnosis of 47,XXY has significant clinical implications for health professional education and postnatal management. [ABSTRACT FROM AUTHOR]

Background: The implementation of genomic testing in pregnancy means that couples have access to more information about their child's genetic make-up before birth than ever before. One of the resulting challenges is the management of genetic variations with unclear clinical significance. This population-based study will help to close this critical knowledge gap through a multidisciplinary cohort study of children with and without genomic copy number variants (CNVs) diagnosed before birth. By comparing children with prenatally-ascertained CNVs to children without a CNV, we aim to (1) examine their developmental, social-emotional and health status; (2) measure the impact of prenatal diagnosis of a CNV on maternal perceptions of child health, behavior and development; and (3) determine the proportion of prenatally-ascertained CNVs of unknown or uncertain significance that are reclassified as benign or pathogenic after 2 or more years. Methods: This study will establish and follow up a cohort of mother-child pairs who have had a prenatal diagnosis with a chromosomal microarray from 2013-2019 in the Australian state of Victoria. Children aged 12 months to 7 years will be assessed using validated, age-appropriate measures. The primary outcome measures will be the Wechsler Preschool and Primary Scale of Intelligence IV (WPSSI-IV) IQ score (2.5 to 7 year old's), the Ages and Stages Questionnaire (12-30 months old), and the Brief Infant- Toddler Social and Emotional Assessment (BITSEA) score. Clinical assessment by a pediatrician will also be performed. Secondary outcomes will be scores obtained from the: Vineland Adaptive Behavior Scale, Maternal Postnatal Attachment Questionnaire, the Vulnerable Child Scale, Profile of Mood States, Parent Sense of Competence Scale. A descriptive analysis of the reclassification rates of CNVs after ≥2 years will be performed. Discussion: This study protocol describes the first Australian cohort study following children after prenatal diagnostic testing with chromosomal microarray. It will provide long-term outcomes of fetal genomic variants to guide evidence-based pre-and postnatal care. This, in turn, will inform future efforts to mitigate the negative consequences of conveying genomic uncertainty during pregnancy. Trial registration: ACTRN12620000446965p; Registered on April 6, 2020. [ABSTRACT FROM AUTHOR]