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Enrichment of the fetal fraction in non-invasive prenatal screening reduces maternal background interference.

ABSTRACT: Measurement of cell-free fetal DNA (cffDNA) is an indispensable process for non-invasive prenatal screening (NIPS). According to recent studies, cffDNA in maternal plasma can be enriched for various lengths of fragments, and a sufficient amount of cffDNA can effectively eliminate background interference on the part of maternal DNA. Therefore, we developed a simple and effective separation method, improved NIPS (iNIPS), that enriches the fetal fraction and improves the accuracy of NIPS for fetal aneuploid detection. We adopted a novel strategy to achieve enrichment of 125-135?bp cell-free DNA (cfDNA) by e-gel electrophoresis. To evaluate clinical performance, we compared NIPS and iNIPS results from 2153 retrospective clinical samples. Of the 22 samples with NIPS results of "no call", 17 samples were reclassified as "unaffected" (9 cases of chr13, 5 cases of chr18, and 3 cases of chr21); 2 samples remained classified as "no call" (1 case of chr18 and 1 case of chr21); and 3 samples were identified as T21 by iNIPS. The average increase in abundance of cfDNA fragments of 125-135?bp was 2.5 times, and the average decrease in maternal background interference was 1.3 times. On this basis, the detection of fetal aneuploidy was highly improved with the fetal fraction as low as 2%; iNIPS achieved 100% sensitivity and 99.90% specificity in retrospective samples.

SUBMITTER: Liang B

PROVIDER: S-EPMC6281613 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Enrichment of the fetal fraction in non-invasive prenatal screening reduces maternal background interference.

Liang Bo B Li Hong H He Quanze Q Li Haibo H Kong Lingyin L Xuan Liming L Xia Yingying Y Shen Jingjing J Mao Yan Y Li Yixue Y Wang Ting T Zhao Yi-Lei YL

Scientific reports 20181205 1

Measurement of cell-free fetal DNA (cffDNA) is an indispensable process for non-invasive prenatal screening (NIPS). According to recent studies, cffDNA in maternal plasma can be enriched for various lengths of fragments, and a sufficient amount of cffDNA can effectively eliminate background interference on the part of maternal DNA. Therefore, we developed a simple and effective separation method, improved NIPS (iNIPS), that enriches the fetal fraction and improves the accuracy of NIPS for fetal ...[more]

PMID: 30518878

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Project description:ObjectiveTo describe our clinical experience across the entire range of fetal-fraction (FF) measurements of a non-invasive prenatal screen (NIPS) that uses whole- genome sequencing (WGS).MethodsWe analyzed retrospectively results from 58 105 singleton pregnancies that underwent NIPS on a customized WGS platform during an 8-month period and assessed clinical test performance for trisomy 21, trisomy 18 and trisomy 13. Pregnancy outcomes were sought for all screen-positive patients and for 18% of screen-negative patients. As differences in outcome-collection response rates could artificially impact test-performance calculations, we computed inferred sensitivity, specificity, positive predictive values (PPV) and negative predictive values adjusted for ascertainment bias.ResultsThe screening test yielded a result for 99.9% (n = 58 048) of patients, meaning that approximately 1 in 1000 patients received a test failure (i.e. test failure rate = 0.1%). Of pregnancies with a test result, 572 (1%) screened positive for one of the common aneuploidies (362 for trisomy 21, 142 for trisomy 18 and 68 for trisomy 13). Informative outcomes were received for 237 (41.4%) patients with a screen-positive result and 3258 (5.7%) of those with a screen-negative result. In the full cohort, inferred sensitivities for trisomy 21, trisomy 18 and trisomy 13 were 99.7%, 96.8% and 94.3%, respectively, and PPVs were 93.1%, 85.2% and 48.4%, respectively. If a FF threshold of 4% had been employed to guard against false negatives, calculated sensitivities for the three aneuploidies would not have changed significantly, yet, importantly, the overall test-failure rate would have increased to 6.6% (n = 3829), impacting 1 in 15 women.ConclusionsOur clinical experience demonstrates that a customized WGS-based NIPS without a FF threshold achieves high accuracy while maintaining a low test-failure rate of 0.1%. As such, alternative strategies to ensure high accuracy of detection of common aneuploidies in samples with low FF (such as redraw after test failure, redrawing at a later gestational age, risk scoring based on FF) are not necessary for this screening approach. © 2019 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Project description:ObjectiveTo identify pregnancies at increased risk for trisomy 13, trisomy 18 or triploidy attributable to low fetal fraction (FF).MethodsA FF-based risk (FFBR) model was built using data from more than 165 000 singleton pregnancies referred for single-nucleotide polymorphism (SNP)-based non-invasive prenatal testing (NIPT). Based on maternal weight and gestational age (GA), FF distributions for normal, trisomy 13, trisomy 18 and triploid pregnancies were constructed and used to adjust prior risks for these abnormalities. A risk cut-off of ≥ 1% was chosen to define pregnancies at high risk for trisomy 13, trisomy 18 or triploidy (high FFBR score). The model was evaluated on an independent blinded set of pregnancies for which SNP-based NIPT did not return a result, and for which pregnancy outcome information was gathered retrospectively.ResultsThe evaluation cohort comprised 1148 cases, of which approximately half received a high FFBR score. Compared with rates expected based on maternal age (MA) and GA, cases with a high FFBR score had a significantly increased rate of trisomy 13, trisomy 18 or triploidy combined (5.7% vs 0.7%; P < 0.001) and also of unexplained pregnancy loss (14.7% vs 10.4%; P < 0.001). For cases that did not receive a high FFBR score, the incidence of a chromosomal abnormality or pregnancy loss was not significantly different from that expected based on MA and GA. In this study cohort, the sensitivity of the FFBR model for detection of trisomy 13, trisomy 18 or triploidy was 91.4% (95% CI, 76.9-98.2%) with a positive predictive value of 5.7% (32/564; 95% CI, 3.9-7.9%).ConclusionsFor pregnancies with a FF too low to receive a result on standard NIPT, the FFBR algorithm identified a subset of cases at increased risk for trisomy 13, trisomy 18 or triploidy. For the remainder of cases, the risk of a fetal chromosomal abnormality was unchanged from that expected based on MA and GA. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Project description:ObjectiveWe and others have previously demonstrated that the size-selection enrichment method could remarkably improve fetal fraction (FF) in the early gestational age (GA, 12-13 weeks), suggesting that 9 or 10 weeks should not be used as a threshold for GA in size-selection noninvasive prenatal screening (NIPS). Here, we assessed whether this method was reliable for detecting fetal chromosomal aneuploidy at the earliest GA (6-8 weeks).MethodsSize-selection NIPS for fetal chromosomal aneuploidy was applied to 208 pregnancy plasma samples (102 male and 106 female fetuses), while the 169 pregnancy samples with male fetuses also underwent standard NIPS. Multivariable linear regression models were used to evaluate the association between fold-change of FF and experimental factors.ResultsThe sensitivity of the cell-free DNA (cfDNA) test in detecting aneuploidy was 100% when screened with FF enrichment, whereas the sensitivity of the same patients was only 62.5% (5/8) without FF enrichment. In the 102 pregnancy samples with male fetuses, FF increased from 6.1% to 15.7%, and the median increase in FF was 2.8-fold with enrichment. Moreover, there was a trend toward an increasing success rate of the cfDNA test from 6 to 13 weeks of gestation, especially when the test success rate reached 100% after 7 weeks with FF enrichment. Multivariate linear regression analysis demonstrated that a lower initial FF, shorter cfDNA size, increased body mass index (BMI), and later GA were all independent predictors of a higher fold-change of FF. Compared with ≤ 120 bp cfDNA fragments, the mean fold-change of FF differences was 0.820 for 121-125 bp, 0.229 for 126-130 bp, - 0.154 for 131-135 bp, - 0.525 for 136-140 bp and - 0.934 for > 140 bp (Ptrend < 0.0001), suggesting that fold-change of FF significantly decreased with cfDNA fragments > 125 bp. These results were statistically significant after adjusting for confounding factors in the models for fold-change of FF.ConclusionsThe FF enrichment method is a reasonable strategy to detect fetal chromosomal aneuploidy in early pregnancy loss with reduced false negatives and increased test success rate after 7 weeks of GA and should be recommended for patients with early pregnancy loss.

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Enrichment of the fetal fraction in non-invasive prenatal screening reduces maternal background interference.

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Enrichment of the fetal fraction in non-invasive prenatal screening reduces maternal background interference.

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