Objectives: We conducted a systematic review and meta-analysis to determine the diagnostic yield of exome sequencing (ES) for prenatal diagnosis of fetal structural anomalies, where karyotype/chromosomal microarray (CMA) is normal.Methods: Following electronic searches of four databases, we included studies with ≥10 structurally abnormal fetuses undergoing ES or whole genome sequencing. The incremental diagnostic yield of ES over CMA/karyotype was calculated and pooled in a meta-analysis. Sub-group analyses investigated effects of case selection and fetal phenotype on diagnostic yield. Results:We identified 72 reports from 66 studies, representing 4350 fetuses. The pooled incremental yield of ES was 31% (95% confidence interval (CI) 26%-36%, p < 0.0001). Diagnostic yield was significantly higher for cases pre-selected for likelihood of monogenic aetiology compared to unselected cases (42% vs. 15%, p < 0.0001). Diagnostic yield differed significantly between phenotypic sub-groups, ranging from 53% (95% CI 42%-63%, p < 0.0001) for isolated skeletal abnormalities, to 2% (95% CI 0%-5%, p = 0.04) for isolated increased nuchal translucency. Conclusion:Prenatal ES provides a diagnosis in an additional 31% of structurally abnormal fetuses when CMA/karyotype is non-diagnostic. The expected diagnostic yield depends on the body system(s) affected and can be optimised by pre-selection of cases following multi-disciplinary review to determine that a monogenic cause is likely. Key pointsWhat's already known about this topic? � Prenatal exome sequencing (ES) increases genetic diagnoses in fetuses with structural abnormalities and a normal karyotype and chromosomal microarray.� Published diagnostic yields from ES are varied and may be influenced by study size, case selection and fetal phenotype.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

BACKGROUND Cell-free fetal DNA (cffDNA) is present in the maternal blood from around 4 weeks gestation and makes up 5%–20% of the total circulating cell-free DNA (cfDNA) in maternal plasma. Presence of cffDNA has allowed development of noninvasive prenatal diagnosis (NIPD) for single-gene disorders. This can be performed from 9 weeks gestation and offers a definitive diagnosis without the miscarriage risk associated with invasive procedures. One of the major challenges is distinguishing fetal mutations in the high background of maternal cfDNA, and research is currently focusing on the technological advances required to solve this problem. CONTENT Here, we review the literature to describe the current status of NIPD for monogenic disorders and discuss how the evolving methodologies and technologies are expected to impact this field in both the commercial and public healthcare setting. SUMMARY NIPD for single-gene diseases was first reported in 2000 and took 12 years to be approved for use in a public health service. Implementation has remained slow but is expected to increase as this testing becomes cheaper, faster, and more accurate. There are still many technical and analytical challenges ahead, and it is vital that discussions surrounding the ethical and social impact of NIPD take account of the considerations required to implement these services safely into the healthcare setting, while keeping up with the technological advances.

The discovery of cell-free fetal DNA (cffDNA) in maternal plasma has enabled a paradigm shift in prenatal testing, allowing for safer, earlier detection of genetic conditions of the fetus. Non-invasive prenatal testing (NIPT) for fetal aneuploidies has provided an alternative, highly efficient approach to first-trimester aneuploidy screening, and since its inception has been rapidly adopted worldwide. Due to the genome-wide nature of some NIPT protocols, the commercial sector has widened the scope of cell-free DNA (cfDNA) screening to include sex chromosome aneuploidies, rare autosomal trisomies and sub-microscopic copy number variants. These developments may be marketed as “expanded NIPT” or “NIPT Plus”, and bring with them a plethora of ethical and practical considerations. Concurrently, cfDNA tests for single gene disorders, termed non-invasive prenatal diagnosis (NIPD), have been developed for an increasing array of conditions but are less widely available. Despite the fact that all these tests utilise the same biomarker, cfDNA, there is considerable variation in key parameters such as sensitivity, specificity and positive predictive value depending on what the test is for. The distinction between diagnostics and screening has become blurred, and there is a clear need for the education of physicians and patients regarding the technical capabilities and limitations of these different forms of testing. Furthermore, there is a requirement for consistent guidelines that apply across health sectors, both public and commercial, to ensure that tests are validated and robust, and that careful and appropriate pre-test and post-test counselling is provided by professionals who understand the tests offered.

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Background Prenatal exome sequencing (ES) for monogenic disorders in fetuses with structural anomalies increases diagnostic yield. In England there is a national trio ES service delivered from two laboratories. To minimise incidental findings and reduce the number of variants investigated, analysis uses a panel of 1205 genes where pathogenic variants may cause abnormalities presenting prenatally. Here we review our laboratory's early experience developing and delivering ES to identify challenges in interpretation and reporting and inform service development. Methods A retrospective laboratory records review from 01.04.2020 to 31.05.2021. Results Twenty‐four of 116 completed cases were identified as challenging including 13 resulting in difficulties in analysis and reporting, nine where trio inheritance filtering would have missed the diagnosis, and two with no prenatal diagnosis; one due to inadequate pipeline sensitivity, the other because the gene was not on the panel. Two cases with copy number variants identified were not detectable by microarray. Conclusions Variant interpretation requires close communication between referring clinicians, with occasional additional examination of the fetus or parents and communication of evolving phenotypes. Inheritance filtering misses ∼5% of diagnoses. Panel analysis reduces but does not exclude incidental findings. Regular review of published literature is required to identify new reports that may aid classification.