Background Cell-free fetal DNA (cffDNA) non-invasive prenatal testing (NIPT) is rapidly expanding, and is being introduced at varying rates depending on country and condition.Objectives Determine accuracy of cffDNA-based NIPT for all conditions. Evaluate influence of other factors on test performance.Search strategy Medline, Embase, CINAHL, Cochrane Library, from 1997 to April 2015.Selection criteria Cohort studies reporting cffDNA-based NIPT performance in singleton pregnancies.Data collection and analysis Bivariate or univariate meta-analysis and subgroup analysis performed to explore influence of test type and population risk. False and inconclusive results were poorly reported across all conditions. Although the test type affected both sensitivity and specificity, there was no evidence that population risk had any effect.Conclusion Performance of cffDNA-based NIPT is affected by condition under investigation. For fetal sex and rhesus D status, NIPT can be considered diagnostic. For trisomy 21, 18, and 13, the lower sensitivity, specificity, and disease prevalence, combined with the biological influence of confined placental mosaicism, designates it a screening test. These factors must be considered when counselling patients and assessing the cost of introduction into routine care.Keywords Cell-free fetal DNA, diagnostic accuracy, non-invasive prenatal testing.Tweetable abstract cffDNA NIPT accuracy high, can be diagnostic for fetal sex and rhesus D, but only screening test in aneuploidy.

BACKGROUND Approximately 50% of pregnancy losses are caused by chromosomal abnormalities, such as aneuploidy. The remainder has an apparent euploid karyotype, but it is plausible that there are cases of pregnancy loss with other genetic aberrations that are not currently routinely detected. Studies investigating the use of exome sequencing and chromosomal microarrays in structurally abnormal pregnancies and developmental disorders have demonstrated their clinical application and/or potential utility in these groups of patients. Similarly, there have been several studies that have sought to identify genes that are potentially causative of, or associated with, spontaneous pregnancy loss, but the evidence has not yet been synthesized. OBJECTIVE AND RATIONALE The objective was to identify studies that have recorded monogenic genetic contributions to pregnancy loss in euploid pregnancies, establish evidence for genetic causes of pregnancy loss, identify the limitations of current evidence, and make recommendations for future studies. This evidence is important in considering additional research into Mendelian causes of pregnancy loss and appropriate genetic investigations for couples experiencing recurrent pregnancy loss. SEARCH METHODS A systematic review was conducted in MEDLINE (1946 to May 2018) and Embase (1974 to May 2018). The search terms ‘spontaneous abortion’, ‘miscarriage’, ‘pregnancy loss’, or ‘lethal’ were used to identify pregnancy loss terms. These were combined with search terms to identify the genetic contribution including ‘exome’, ‘human genome’, ‘sequencing analysis’, ‘sequencing’, ‘copy number variation’, ‘single-nucleotide polymorphism’, ‘microarray analysis’, and ‘comparative genomic hybridization’. Studies were limited to pregnancy loss up to 20 weeks in humans and excluded if the genetic content included genes that are not lethal in utero, PGD studies, infertility studies, expression studies, aneuploidy with no recurrence risk, methodologies where there is no clinical relevance, and complex genetic studies. The quality of the studies was assessed using a modified version of the Newcastle–Ottawa scale. OUTCOMES A total of 50 studies were identified and categorized into three themes: whole-exome sequencing studies; copy number variation studies; and other studies related to pregnancy loss including recurrent molar pregnancies, epigenetics, and mitochondrial DNA aberrations. Putatively causative variants were found in a range of genes, including CHRNA1 (cholinergic receptor, nicotinic, alpha polypeptide 1), DYNC2H1 (dynein, cytoplasmic 2, heavy chain 1), and RYR1 (ryanodine receptor 1), which were identified in multiple studies. Copy number variants were also identified to have a causal or associated link with recurrent miscarriage. WIDER IMPLICATIONS Identification of genes that are causative of or predisposing to pregnancy loss will be of significant individual patient impact with respect to counselling and treatment. In addition, knowledge of specific genes that contribute to pregnancy loss could also be of importance in designing a diagnostic sequencing panel for patients with recurrent pregnancy loss and also in understanding the biological pathways that can cause pregnancy loss.

Although technically possible, few clinical laboratories across the world have implemented non-invasive prenatal diagnosis (NIPD) for selected single-gene disorders, mostly owing to the elevated costs incurred. Having previously proven that NIPD for X-linked disorders can be feasibly implemented in clinical practice, we have now developed a test for the NIPD of an autosomal-recessive disorder, spinal muscular atrophy (SMA). Cell-free DNA was extracted from maternal blood and prepared for massively parallel sequencing on an Illumina MiSeq by targeted capture enrichment of single-nucleotide polymorphisms across a 6 Mb genomic window on chromosome 5 containing the SMN1 gene. Maternal, paternal and proband DNA samples were also tested for haplotyping purposes. Sequencing data was analysed by relative haplotype dosage (RHDO). Six pregnant SMA carriers and 10 healthy pregnant donors were recruited through the NIPSIGEN study. Inheritance of the maternally and paternally derived alleles of the affected SMN1 gene was determined in the foetus by RHDO analysis for autosomal-recessive disorders. DNA from the proband (for SMA carriers) or an invasively obtained foetal sample (for healthy pregnant donors) was used to identify the maternal and paternal reference haplotypes associated with the affected SMN1 gene. Results for all patients correlated with known outcomes and showed a testing specificity and sensitivity of 100%. On top of showing high accuracy and reliability throughout the stages of validation, our novel test for NIPD of SMA is also affordable and viable for implementation into clinical service.

ObjectiveDevelopment of an accurate and affordable test for the non‐invasive prenatal diagnosis of Duchenne and Becker muscular dystrophies (DMD/BMD) to implement in clinical practice.MethodCell‐free DNA was extracted from maternal blood and prepared for massively parallel sequencing on an Illumina MiSeq by targeted capture enrichment of single nucleotide polymorphisms (SNPs) across the dystrophin gene on chromosome X. Sequencing data were analysed by relative haplotype dosage.ResultsSeven healthy pregnant donors and two pregnant DMD carriers all bearing a male fetus were recruited through the non‐invasive prenatal diagnosis for single gene disorders study. Non‐invasive prenatal diagnosis testing was conducted by relative haplotype dosage analysis for X‐linked disorders where the genomic DNA from the chorionic villus sampling (for healthy pregnant donors) or from the proband (for pregnant DMD carriers) was used to identify the reference haplotype. Results for all patients showed a test accuracy of 100%, when the calculated fetal fraction was >4% and correlated with known outcomes. A recombination event was also detected in a DMD patient.ConclusionOur new test for NIPD of DMD/BMD has been shown to be accurate and reliable during initial stages of validation. It is also feasible for implementation into clinical service. © 2016 The Authors. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

The identification of cell-free fetal DNA circulating in maternal blood combined with technological developments, in particular next-generation sequencing, is enabling the development of safer prenatal diagnosis. While this technology has been widely applied as a highly sensitive screening test for aneuploidy, there has been relatively little clinical application for the diagnosis of monogenic disorders. In the UK, we have established non-invasive prenatal diagnosis (NIPD) as a clinical service for a range of inherited disorders. The results from NIPD do not require confirmation by invasive testing and are welcomed by patients and health professionals alike. Here, we describe the technical approaches used, current practice and outline recommendations for best practice when delivering an NIPD service from an accredited laboratory. © 2017 John Wiley & Sons, Ltd.