Clinical implementation of routine screening for fetal trisomies in the UK NHS: cell-free DNA test contingent on results from first-trimester combined test

Is intermediate risk really intermediate? Comparison of karyotype and non-invasive prenatal testing results of pregnancies at intermediate risk of trisomy 21 on maternal serum screening

The purpose of this study was to assess the additional contribution of karyotyping compared with genome-wide non-invasive prenatal testing (NIPT) for pregnancies at intermediate risk for trisomy 21 (T21), calculated using the maternal serum screening without major structural anomalies detected through sonography. Karyotype results of all pregnancies undergoing invasive prenatal diagnostic testing between January 2013 and March 2022 were obtained from a large hospital-based laboratory. Pregnancies with no major structural anomalies on ultrasound (including soft markers) and an intermediate risk for T21 on maternal serum screening were included in this study. The additional contribution of karyotyping for abnormal karyotype results was calculated after excluding results that could theoretically be identified with genome-wide NIPT. Among the 511 pregnancies analyzed, 13 (2.54%) were found to have abnormal karyotype results, 9 (1.76%) of which could theoretically have been detected with genome-wide NIPT. Within the cohort, 6/263 (2.28%) of women aged 35 years and older, and 3/248 (1.20%) of women younger than 35 years had results that could have been detected with genome-wide NIPT. After excluding results detectable using genome-wide NIPT, the additional contribution of karyotyping was found as 4/502 (0.79%) for the entire cohort, 2/257 (0.77%) for women aged 35 years and older, 2/245 (0.81%) for women younger than 35 years. Of the 511 examined pregnancies at intermediate risk for T21 by maternal serum screening, genome-wide NIPT would have failed to detect 4 of 13 abnormal karyotype results. The findings hold importance in guiding couples' informed decision-making processes regarding their choice of genetic screening and diagnostic testing in case of intermediate risk for T21.

The value of combined detailed first-trimester ultrasound-biochemical analysis for screening fetal aneuploidy in the era of non-invasive prenatal testing

PURPOSE

This study aimed to investigate the performance, cost-effectiveness and additional findings of combined detailed ultrasound and biochemical screening for risks of major fetal trisomies in the first-trimester.

METHODS

This is a retrospective analysis study, we estimated the risk of trisomies 21, 18 and 13 based on maternal age, fetal nuchal translucency thickness, nasal bone, ductus venosus pulsatility index velocity, tricuspid regurgitation, fetal heart rate, free beta-human chorionic gonadotropin, and pregnancy-associated plasma protein A in singleton pregnant women, and performed non-invasive prenatal testing for women with risks of trisomy 21 between 1:500 and 1:300. Invasive diagnostic testing was performed for women with positive or failed non-invasive prenatal testing result and in the high-risk group of this screening method. The direct costs were compared between this strategy and the non-invasive prenatal testing which alone used as first-line screening for all pregnant women.

RESULTS

Among 25,155 singleton pregnant women who underwent screening, 24,361 were available for analysis, of these, 194 cases underwent non-invasive prenatal testing. Among the 24,361 women, 39, 19, and 7 had trisomies 21, 18 and 13, respectively. The use of this strategy could potentially detect approximately 94.87% of trisomy 21 cases, 100% of trisomy 18 cases, and 100% of trisomy 13 cases, with false-positive rates of 2.49%, 0.41%, and 0.49%, respectively. The overall detection rate and overall false-positive rates were 96.92% and 2.52%, respectively. The detection rate was 100% in the advanced age group and 94.12% in the general age group. Additionally, structural abnormalities were detected in 137 fetuses, and 44 fetuses had other chromosomal abnormalities. The total cost of this strategy was $3,730,843.30, and the cost per person tested was $153.15. The total cost of using non-invasive prenatal testing as the first-line strategy would be $6,813,387.04 and the cost per person tested was $279.68.

CONCLUSIONS

Our strategy is an efficient and cost-effective approach for detecting major trisomies and identifying more fetuses with a potential abnormality. Therefore, this strategy is a valuable screening method and highly feasible in the clinical setting.

Current controversies in prenatal diagnosis: Noninvasive prenatal testing should replace other screening strategies for fetal trisomies 13, 18, 21

This is a written summary of the oral debate presented at the International Society for Prenatal Diagnosis annual conference in Edinburgh in 2023. The topic under debate is whether noninvasive prenatal testing (NIPT) using cell-free fetal DNA should replace other screening strategies for the detection of fetal trisomies 13, 18, 21. There is no disagreement that NIPT is far more sensitive and has better positive predictive values for identifying trisomies 13, 18, and 21 than traditional screening approaches using biochemical markers and measurement of nuchal translucency. The major issue lies in the potential adverse consequences associated with abandoning traditional screening methods. The source of disagreement stems primarily from whether you consider the role of ultrasound in the context of screening to be strictly for nuchal translucency measurement or whether it should be combined with a fetal anatomy scan. The debate featured two experts who presented evidence in favor of each argument.

First Trimester Contingent Screening for Aneuploidies with Cell-Free Fetal DNA in Singleton Pregnancies - a Swiss Single Centre Experience

Introduction

Switzerland was amongst the first countries to offer cell-free fetal DNA (cffDNA) testing covered by the health insurance to pregnant women with a risk ≥ 1:1000 for trisomies at first trimester combined screening (FTCS). The aim of this study is to evaluate the implementation of this contingent model in a single tertiary referral centre and its effect on gestational age at diagnosing trisomy 21.

Materials and Methods

Between July 2015 and December 2020 all singleton pregnancies at 11-14 weeks of gestation without major fetal malformation were included and stratified according to their risk at FTCS. Statistical analysis was performed by GraphPad Version 9.1 for Windows.

Results

4424 pregnancies were included. Of 166 (3.8%) pregnancies with a NT ≥ 3.5 mm and/or a risk ≥ 1:10 at FCTS, 130 (78.3%) opted for direct invasive testing. 803 (18.2%) pregnancies had an intermediate risk, 692 (86.2%) of them opted for cffDNA first. 3455 (78.1%) pregnancies had a risk < 1:1000. 63 fetuses were diagnosed with trisomy 21, 47 (74.6%) directly by invasive procedures after FTCS, 16 (25.4%) by cffDNA first.

Conclusions

Most women choose cffDNA or invasive testing as second tier according to national guidelines. Despite the delay associated with cffDNA testing after FCTS, 75% of all trisomy 21 are still diagnosed in the first trimester with this contingent screening model.

The role of ultrasound in first-trimester screening after the introduction of NIPT as a service of public health insurance - a consensus statement of the Fetal Medicine Foundation (FMF) Germany

Combined first-trimester screening (FTS) and noninvasive prenatal testing (NIPT) have been proven to be reliable noninvasive procedures to detect the most common chromosomal abnormalities (trisomies 21, 18, 13) in the first trimester. The aim of this paper is to demonstrate the strengths and limitations of these two procedures and to give a consensus statement of the Fetal Medicine Foundation (FMF) Germany on how to use the two techniques in the first trimester after the introduction of NIPT as a service of the statutory health insurance companies in Germany.

Discordant performances of non-invasive prenatal testing for foetal trisomy 21 screening in subgroups of pregnancies

BACKGROUND

Non-invasive prenatal testing (NIPT) has been widely adopted as an approach for foetal aneuploidy screening. This study was to evaluate the performance of NIPT for foetal T21 detection in subgroups of pregnancies and the correlation between Z-score and discordant positive predictive values (PPVs).

METHODS

We retrospectively reviewed the NIPT results among 22361 pregnancies undergoing combined second-trimester screening (cSTS) previously. Sixty-four cases with positive NIPT results for foetal T21 were validated by invasive prenatal diagnosis.

RESULTS

In pregnancies with cSTS-T21 low-, intermediate-, and high-risk, the PPVs at NIPT were 14.3%, 64.3%, and 86.4%, respectively. Mean Z-scores of positive NIPT cases with cSTS-T21 high- and intermediate-risk were comparable, while were higher than that of cases with pre-test low-risk. Furthermore, PPVs for positive NIPT cases at 3 < Z < 5, 5 ≤ Z < 9, and Z ≥ 9 were 16.7%, 63.2%, and 100.0%, respectively.

CONCLUSIONS

This study suggested that Z-score value of positive cases might be associated with discordant PPVs for T21 screening in subgroups of pregnancies.

A new contingent screening strategy increased detection rate of trisomy 21 in the first trimester

BACKGROUND

Although the traditional contingent screening strategy is effective, there are still undetected low-risk trisomy 21. This study aims to define appropriate cut-off values of serum biochemical markers at low-risk and develop a strategy for sequential prenatal testing associated with first-trimester screening to increase the detection rate of trisomy 21.

METHODS

This was a 9-year retrospective analysis of singleton pregnant women who underwent serum biochemical screening or combined first-trimester screening (CFTS) in the first trimester. For the low-risk group, the cut-off values of the serum biochemical markers were adjusted to determine the appropriate detection efficiency. Gravidas with abnormal serum biochemical markers at low-risk were advised to undergo further non-invasive prenatal screening (NIPS), whereas others continued with routine prenatal care.

RESULTS

When cut-off values of free beta subunit of human chorionic gonadotropin (free β-hCG) multiples of the median (MoM) or pregnancy-associated plasma protein A (PAPP-A) MoM were defined with ≥ 2.75 or ≤ 0.5, 7.72% (2,194/28,405) in the serum biochemical screening group and 12.36% (4,005/32,403) in CFTS group could be detected as abnormal results for further NIPS. Finally, 55.56% (5/9) and 85.71% (6/7) of trisomy 21 cases with false-negative results were detected, and the overall detection rate for trisomy 21 was improved by 10.64% (5/47) and 12.77% (6/47), respectively.

CONCLUSIONS

The new contingent screening strategy can increase the detection rate of trisomy 21 compared with the traditional contingent screening strategy.

Non-invasive prenatal testing for the diagnosis of congenital abnormalities: Insights from a large multicenter study in southern China

Although non-invasive prenatal testing (NIPT) is widely used to detect fetal abnormalities, the results of NIPT vary by population, and data for the screening efficiency of NIPT positive predictive value (PPV) from different populations is limited. Herein, we retrospectively analyzed the NIPT results in a large multicenter study involving 52,855 pregnant women. Depending on gestational age, amniotic fluid or umbilical cord blood was extracted for karyotype and/or chromosome microarray analysis (CMA) in NIPT-positive patients, and the PPV and follow-up data were evaluated to determine its clinical value. Among the 52,855 cases, 754 were NIPT-positive, with a positivity rate of 1.4%. Karyotype analysis and/or CMA confirmed 323 chromosomal abnormalities, with a PPV of 45.1%. PPV for trisomy 21 (T21), trisomy 18 (T18), trisomy 13 (T13), sex chromosomal aneuploidies (SCAs), and copy number variations (CNVs) were 78.9, 35.3, 22.2, 36.9, and 32.9%, respectively. The PPVs for T21, T18, and T13 increased with age, whereas the PPVs for SCAs and CNVs had little correlation with age. The PPV was significantly higher in patients with advanced age and abnormal ultrasound. The NIPT results are affected by population characteristics. NIPT had a high PPV for T21 and a low PPV for T13 and T18, and screening for SCAs and CNVs showed clinical significance in southern China.

Does a High-Risk (>1/50) Result for First-Trimester Combined Screening Always Entail Invasive Testing? Which Patients from This Group Might Benefit from cfDNA Testing?

Currently, cell-free DNA (cfDNA) is offered as part of a contingent screening for patients with a first-trimester combined test (FCT) risk between 1/50 and 1/250. However, most aneuploidies are within the group of patients with a risk above 1/10. An observational, retrospective, and multi-centric study was carried out, to evaluate the theorical performance of lowering the cut-off point for the high-risk group from 1/50 to 1/10. Out of the 25,920 patients included, 25,374 (97.9%) consented to the cfDNA contingent screening for aneuploidies. With the proposed strategy, knowing that the detection rate (DR) of cfDNA testing for trisomy 21 is 99.7%, the DR for trisomy 21 would have stayed in a 93.2%, just as it was with the current strategy. In this instance, 267 (1.1%) invasive tests would have been performed, while the current strategy had a total of 307 (1.2%). The false positive rate (FPR) rate would have stayed at 5.2% in both scenarios. In conclusion, the contingent screening of aneuploidies based in the result of the FCT, offering the analysis of cfDNA to patients with an intermediate risk after lowering the cut-off point from 1/50 to 1/10, is a valid alternative that might maintain the current detection rates and avoid the complications associated with invasive testing.

First Trimester Screening - Current Status and Future Prospects After Introduction of Non-invasive Prenatal Testing (NIPT) at a Tertiary Referral Center

Objective To investigate the uptake of different components of first trimester screening (FTS) and the impact on invasive diagnostic testing (IPT) since the introduction of non-invasive prenatal testing (NIPT) at a level III center. Methods Retrospective data analysis was conducted for singleton pregnancies that presented for FTS between 01/2019-12/2019 (group 1, n = 990). Patients were categorized into three risk groups: low risk for trisomy 21 (< 1 : 1000), intermediate risk (1 : 101-1 : 1000) and high risk (≥ 1 : 100). Uptake of NIPT and IPT was analyzed for each of the risk groups. Results were compared to a previous cohort from 2012/2013 (immediately after the introduction of NIPT, group 2, n = 1178). Results Group 1 showed a significant increase in the use of NIPT as part of FTS (29.5% vs. 3.7% for group 2, p = 0.001) in all three risk groups. Overall IPT rates were lower in group 1 (8.6%) vs. group 2 (11.3%, p = 0.038), mainly due to a significant reduction of IPT in the intermediate risk group. IPT rates in the high-risk group remained stable over time. Conclusion Appropriate clinical implementation of NIPT is still currently a challenge for prenatal medicine experts. Our data suggest that widespread uptake of NIPT is becoming more common these days; however, a contingent approach might prevent redundant uptake.

Whole genome non-invasive prenatal testing in prenatal screening algorithm: clinical experience from 12,700 pregnancies

BACKGROUND

A fast adoption of a non-invasive prenatal testing (NIPT) in clinical practice is a global tendency last years. Firstly, in Russia according a new regulation it was possible to perform a widescale testing of pregnant women in chromosomal abnormality risk. The aim of the study-to assess efficiency of using NIPT as a second-line first trimester screening test in Moscow.

METHODS

Based on the first trimester combined prenatal screening results 12,700 pregnant women were classified as a high-risk (cut-off ≥ 1:100) and an intermediate-risk (cut-off 1:101 - 1:2500) groups followed by whole genome NIPT. Women from high-risk group and those who had positive NIPT results from intermediate-risk group were considered for invasive prenatal diagnostic.

RESULTS

258 (2.0%) samples with positive NIPT results were detected including 126 cases of trisomy 21 (T21), 40 cases of T18, 12 cases of T13, 41 cases of sex chromosome aneuploidies (SCAs) and 39 cases of rare autosomal aneuploidies (RAAs) and significant copy number variations (CNVs). Statistically significant associations (p < 0.05) were revealed for fetal fraction (FF) and both for some patient's (body mass index and weight) and fetus's (sex and high risk of aneuploidies) characteristics. NIPT showed as a high sensitivity as specificity for common trisomies and SCAs with an overall false positive rate 0.3%.

CONCLUSIONS

NIPT demonstrated high sensitivity and specificity. As a second-line screening test it has shown a high efficiency in detecting fetus chromosomal anomalies as well as it could potentially lower the number of invasive procedures in pregnant women.

Antenatal screening for chromosomal abnormalities

Screening for chromosomal disorders, especially for trisomy 21, has undergone a number of changes in the last 50 years. Today, cell-free DNA analysis (cfDNA) is the gold standard in screening for trisomy 21. Despite the advantages that cfDNA offers in screening for common trisomies, it must be recognized that it does not address many other chromosomal disorders and any of the structural fetal anomalies. In the first trimester, the optimal approach is to combine an ultrasound assessment of the fetus, which includes an NT measurement, with cfDNA testing. If fetal structural defects are detected or if the NT thickness is increased, an amniocentesis or a CVS with at least chromosomal microarray should be offered.

Population contingent cfDNA screening implementation: increasing diagnostic accuracy and reducing invasive testing. 6 years results in a single center

OBJECTIVES

In 2018, a contingent screening program was implemented in the community of Castilla y Leon (Spain). This study aimed to compare the results achieved in the University Hospital of Salamanca during the three years of contingent screening (2018-2020) with those of the previous three years (2015-2017) to assess the modification in the rate of trisomies detection and the number of invasive tests.

METHODS

A total of 9903 singleton pregnancies without malformations nor nuchal translucency >p99 were included. 5165 patients underwent combined screening and 4738 had contingent screening based on the combined test risk. In the combined test group, women were offered an invasive test if the risk was ≥1:270 whilst risks under 1:270 were considered low risks, and no further testing was offered. In the contingent screening group, invasive testing was offered if the risk was ≥1:100 (≥1:50 from 2020 onwards) whilst cfDNA was offered if the combined test risk was between 1:100 to 1:1000 (1:50-1:1000 from 2020 onwards). When risk was <1:1000, no further testing was offered.

RESULTS

There were 30 cases of trisomy 21 throughout the 6 years of study. 4 cases had risks <1:270 and were diagnosed by cfDNA. Risk >1:1000 threshold for contingent test detected 100% T21. There were no false-negative results. "No-call" cfDNA results were minimized by repeating blood collection two weeks later, as fetal fraction was doubled. Invasive testing had a drop rate of 84% after contingent screening implementation.

DISCUSSION

The implementation of population-based contingent screening significantly reduces the number of invasive tests without lowering diagnostic accuracy. To achieve the maximum efficiency of the program, it is important to know the best cut-offs according to the population where the program is to be implemented. The number of uninformative results due to low fetal fraction (FF) can be reduced by repeating the test 2 weeks after the initial extraction: this increases the FF to twice the initial one, achieving informative results and avoiding unnecessary invasive tests.

Audit of the first > 7500 noninvasive prenatal aneuploidy tests in a Swiss genetics center

Objectives

Noninvasive prenatal testing (NIPT) is actually the most accurate method of screening for fetal chromosomal aberration (FCA). We used pregnancy outcome record to evaluate a complete data set of single nucleotide polymorphism-based test results performed by a Swiss genetics center.

Materials and methods

The Panorama^® test assesses the risk of fetal trisomies (21, 18 and 13), gonosomal aneuploidy (GAN), triploidy or vanishing twins (VTT) and five different microdeletions (MD). We evaluated all 7549 test results meeting legal and quality requirements taken in women with nondonor singleton pregnancies between April 2013 and September 2016 classifying them as high or low risk. Follow-up ended after 9 months, data collection 7 months later.

Results

The Panorama^® test provided conclusive results in 96.1% of cases, detecting 153 FCA: T21 n = 76, T18 n = 19, T13 n = 15, GAN n = 19, VTT n = 13 and MD n = 11 (overall prevalence 2.0%). Pregnancy outcome record was available for 68.6% of conclusive laboratory results, including 2.0% high-risk cases. In this cohort the Panorama^® test exhibited 99.90% sensitivity for each trisomy; specificity was 99.90% for T21, 99.98% for T18 and 99.94% for T13. False positive rate was 0.10% for T21, 0.02% for T18 and 0.06% for T13.

Conclusion

SNP-based testing by a Swiss genetics center confirms the expected accuracy of NIPT in FCA detection.

Performance of a universal prenatal screening program incorporating cell-free fetal DNA analysis in Ontario, Canada

BACKGROUND:

The emergence of cell-free fetal DNA (cfDNA) testing technology has disrupted the landscape of prenatal screening for trisomies 21 (T21) and 18 (T18). Publicly funded systems around the world are grappling with how to best integrate this more accurate but costly technology, as there is limited evidence about its incremental value in real-world conditions. The objectives of this study were to describe the population-based performance of Ontario’s prenatal screening program, which incorporates publicly funded cfDNA screening for specific indications, and the effect of cfDNA testing on the screening and diagnostic choices made by pregnant people.

METHODS:

We conducted a retrospective, descriptive cohort study using routinely collected data from Better Outcomes & Registry Network (BORN) Ontario, which captures linked population data for prenatal and neonatal health encounters across Ontario. We included all singleton pregnancies with an estimated due date between Sept. 1, 2016, and Mar. 31, 2019, that underwent publicly funded prenatal screening in Ontario, and a comparison cohort from Apr. 1, 2012, and Mar. 31, 2013. We assessed performance of the screening program for the detection of T21 or T18 by calculating sensitivity, specificity, positive predictive value and negative predictive value against diagnostic cytogenetic results or birth outcomes. We assessed the impact of the program by calculating the proportion of T21 screen-positive pregnancies undergoing subsequent cfDNA screening and invasive prenatal diagnostic testing.

RESULTS:

The study cohort included 373 682 pregnancies. The prenatal screening program had an uptake of 69.9%, a screen-positive rate and sensitivity of 1.6% and 89.9% for T21, and 0.2% and 80.5% for T18, respectively. The test failure rate for cfDNA screening was 2.2%. Invasive prenatal diagnostic testing decreased from 4.4% in 2012–2013 to 2.4% over the study period; 65.2% of pregnant people who received a screen-positive result from cfDNA testing went on to have invasive prenatal diagnostic testing.

INTERPRETATION:

This publicly funded screening program, incorporating cfDNA analysis for common aneuploidies, showed robust performance, a substantial reduction in invasive prenatal diagnostic testing and that pregnant people exercise autonomy in their choices about prenatal screening and diagnosis.

Contingent prenatal screening for frequent aneuploidies with cell-free fetal DNA analysis

OBJECTIVE

To analyze the results of contingent screening for common aneuploidies at our center from June 2017 to June 2019.

MATERIALS AND METHODS

Traditional screening tests were performed using a combination of biochemical markers and ultrasound measurements in the first and second trimesters to assess the risk of trisomies 21 (T21), 18 (T18) and 13 (T13). Cell-free DNA (cf-DNA) testing was offered (Harmony test) to pregnant women at high risk (>1/280 for T21 and > 1/150 for T13 and T18) and a normal early morphology scan. In positive cases, prenatal sampling was strongly recommended to confirm the results by gold standard methods (QF-PCR and karyotyping). Newborns' phenotypes were corroborated after birth in all cases.

RESULTS

In this prospective study, 8153 pregnant women were enrolled, resulting in 390 at high risk according to traditional screening tests. cfDNA testing was offered to 383 women. Traditional screening tests showed a false negative rate of 9.68% for T21. Traditional test sensitivity for T21 was 90.3%, for a false positive rate of 4.17% and a positive predictive value of 7.6%. The positive and negative predictive value for cfDNA testing was 100%. The approach used avoided invasive procedures in 91.3% of women at high risk. The prevalence of chromosomal abnormalities in the population analyzed was 1 in 164, and 1 in 210 for T21.

CONCLUSIONS

Our results show that offering cf-DNA testing to women at high risk in traditional tests (including those with risks >1 in 50) significantly reduces false positives and, therefore, the number of invasive tests. Extending the use of cf-DNA testing to intermediate risk categories may be cost effective.

Utilization and uptake of clinical genetics services in high-income countries: A scoping review

Ongoing rapid growth in the need for genetic services has the potential to severely strain the capacity of the clinical genetics workforce to deliver this care. Unfortunately, assessments of the scale of this health policy challenge and potential solutions are hampered by the lack of a consolidated evidence base on the growth in genetic service utilization. To enable health policy research and strategic planning by health systems in this area, we conducted a scoping review of the literature on the utilization and uptake of clinical genetics services in high-income countries published between 2010 and 2018. One-hundred-and-ninety-five unique studies were included in the review. Most focused on cancer (85/195; 44%) and prenatal care (50/195; 26%), which are consistently the two areas with the greatest volume of genetic service utilization in both the United States and other high-income countries. Utilization and uptake rates varied considerably and were influenced by contextual factors including health system characteristics, provider knowledge, and patient preferences. Moreover, growth in genetic service utilization appears to be driven to a significant degree by technological advances and the integration of new tests into clinical care. Our review highlights both the policy challenge posed by the rapid growth in the utilization of genetic services and the variability in this trend across clinical indications and health systems.

Cell-free DNA and RNA-measurement and applications in clinical diagnostics with focus on metabolic disorders

Circulating cell-free DNA (cfDNA) and RNA (cfRNA) hold enormous potential as a new class of biomarkers for the development of noninvasive liquid biopsies in many diseases and conditions. In recent years, cfDNA and cfRNA have been studied intensely as tools for noninvasive prenatal testing, solid organ transplantation, cancer screening, and monitoring of tumors. In obesity, higher cfDNA concentration indicates accelerated cellular turnover of adipocytes during expansion of adipose mass and may be directly involved in the development of adipose tissue insulin resistance by inducing inflammation. Furthermore, cfDNA and cfRNA have promising diagnostic value in a range of obesity-related metabolic disorders, such as nonalcoholic fatty liver disease, type 2 diabetes, and diabetic complications. Here, we review the current and future applications of cfDNA and cfRNA within clinical diagnostics, discuss technical and analytical challenges in the field, and summarize the opportunities of using cfDNA and cfRNA in the diagnostics and prognostics of obesity-related metabolic disorders.

First-trimester prediction of small-for-gestational age in pregnancies at false-positive high or intermediate risk for fetal aneuploidy

OBJECTIVES

To explore the risk of small-for-gestational age (SGA) and fetal growth restriction (FGR) and to test the performance of first-trimester screening for SGA and FGR in women with a false-positive high or intermediate risk for aneuploidy.

METHODS

This was a prospective cohort study of women with a singleton pregnancy attending for a routine first-trimester scan. The risks of aneuploidy and preterm SGA (defined as birth weight < 10^th percentile with delivery before 37 weeks) were determined according to Fetal Medicine Foundation algorithms. In non-malformed euploid pregnancies, the predictive performance of both the aneuploidy and preterm SGA risks was evaluated for SGA, FGR (defined as birth weight < 3^rd centile), preterm SGA and early SGA (delivery before 34 weeks), using receiver-operating-characteristics (ROC) curve analysis, in those with a high or intermediate risk of aneuploidy and in the overall population.

RESULTS

A total of 2053 pregnancies were included in the analysis, of which 191 (9.3%) were at high or intermediate risk for aneuploidy (≥ 1/1000) and 304 (14.8%) were at high risk for preterm SGA (≥ 1/100). In total, there were 140 (6.8%) cases of SGA, 61 (3.0%) of FGR, 44 (2.1%) of preterm SGA and 33 (1.6%) of early SGA. Among women with a false-positive high or intermediate risk for aneuploidy, the rates of SGA, FGR, preterm SGA and early SGA were 13.6% (26/191), 7.9 % (15/191), 6.8% (13/191) and 5.8% (11/191), respectively. Compared with women with a first-trimester low risk for preterm SGA, regardless of aneuploidy risk, those with a high risk for preterm SGA and a high or intermediate risk for aneuploidy had relative risks for SGA, FGR, preterm SGA and early SGA of 6 (95% CI, 3.9-9), 9.2 (95% CI, 5.1-16.5), 13.4 (95% CI, 6.9-26.1) and 17.6 (95% CI, 8.1-38.2), respectively. The predictive performance for SGA of the preterm SGA algorithm was higher in women at high or intermediate risk for aneuploidy than in the overall population (area under the ROC curve (AUC), 0.8 vs 0.7; P < 0.001). Among women at high or intermediate risk for aneuploidy, the predictive performance of the preterm SGA algorithm was better than that of the aneuploidy algorithm for SGA (AUC, 0.80 vs 0.58; P = 0.003), preterm SGA (AUC, 0.85 vs 0.65; P = 0.013) and early SGA (AUC, 0.86 vs 0.60; P = 0.002).

CONCLUSION

In women with a first-trimester false-positive high or intermediate risk of aneuploidy, further screening for SGA allows stratification of the risk for fetal growth disorders. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.

Prenatal screening for trisomy 21: a comparative performance and cost analysis of different screening strategies

Background

Prenatal screening for chromosome aneuploidies have constantly been evolving, especially with the introduction of cell-free fetal DNA (cfDNA) screening in the most recent years. This study compares the performance, costs and timing of test results of three cfDNA screening implementation strategies: contingent, reflex and primary.

Methods

We modelled enhanced first trimester screening (eFTS) as the first-tier test in contingent or reflex strategies. cfDNA test was performed contingent on or reflex from eFTS results. A comparison was made between cfDNA screening using sequencing technology and Rolling Circle Amplification (RCA)/imaging solution. All model assumptions were based on results from previous publications or information from the Ontario prenatal screening population.

Results

At an eFTS risk cut-off of ≥1/1000, contingent and reflex cfDNA screening have the same detection rate (DR) (94%) for trisomy 21. Reflex cfDNA screening using RCA/Imaging solution provided the lowest false positive rate and cost. The number of women requiring genetic counselling and diagnostic testing was significantly reduced and women received their cfDNA screening result 9 days sooner compared with the contingent model. While primary cfDNA screening improved the trisomy 21 DR by 3–5%, it was more costly and more women required diagnostic testing.

Conclusion

Reflex cfDNA screening is the most cost-effective prenatal screening strategy. It can improve the efficiency of prenatal aneuploidy screening by reducing the number of patient visits and providing more timely results.

First-trimester screening based on cell-free DNA vs combined screening: A randomized clinical trial on women's experience

OBJECTIVE

To compare women's experience of first-trimester combined screening (FTCS), with women's experience of an approach that uses the combination of a detailed early anatomy scan and cell-free DNA (cfDNA) analysis.

METHODS

This was single-center, open label, parallel group, randomized clinical trial. Pregnant women were randomized at the time of their first prenatal visit to either a policy of first-trimester risk assessment based on FTCS, or to a policy of first-trimester risk assessment based on ultrasound findings and cfDNA. FTCS included ultrasound evaluation with crown-rump length, nuchal translucency (NT) measurement, and a detailed ultrasound scan, along with biochemistry (PAPP-A and free beta hCG). In this group, invasive diagnostic testing was offered to patients with risk >1 in 100, or NT >3.5 mm, or any fetal abnormalities on ultrasound. Women randomized in the intervention group received an approach of first-trimester risk assessment based on ultrasound findings and cfDNA. cfDNA analysis included a simultaneous microarray-based assay of non-polymorphic (chromosomes 13, 18, 21, X and Y) and polymorphic loci to estimate chromosome proportion and fetal fraction. In the intervention group, invasive diagnostic testing was offered to patients with abnormal cfDNA screening results, or NT >3.5 mm, or any fetal abnormalities on ultrasound. Participants received pre-test and post-test questionnaires regarding to measure reassurance, satisfaction, and anxiety. The primary outcome was the post-test reassurance, defined as mean score of reassurance post-test questionnaire. The effect of the assigned screening test on the mean of each outcome was quantified as mean difference (MD) with 95% confidence interval (CI).

RESULTS

Forty women with singleton gestations were enrolled in the trial. Mean score for reassurance was significantly higher in the cfDNA group compared to the FTCS group in the pre-test questionnaire (MD 0.80 points, 95% CI 0.27 to 1.33) and in the post-test questionnaire (MD 16.50 points, 95% CI 2.18 to 30.82). Women randomized to the cfDNA group had higher satisfaction and lower mean anxiety score as assessed in the STAI pre-test questionnaire.

CONCLUSIONS

First-trimester risk assessment for fetal aneuploidy with a combination of a detailed ultrasound examination and cfDNA is associated with better maternal reassurance and better maternal satisfaction compared to the standard first-trimester combined screening with nuchal translucency, and biochemistry.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04077060.

Incidence of chromosomal abnormalities in fetuses with first trimester ultrasound anomalies and a low-risk cell-free DNA test for common trisomies

OBJECTIVE

To examine the incidence and type of chromosomal abnormalities in fetuses with first trimester ultrasound anomalies and a low-risk cfDNA test for common trisomies.

METHODS

In 486 singleton pregnancies undergoing invasive testing after combined screening, a detailed first trimester ultrasound assessment was carried out and a maternal blood sample was sent for cfDNA analysis. Ultrasound and cfDNA data were analyzed in relation to fetal karyotype.

RESULTS

Invasive testing demonstrated a chromosomal abnormality in 157 (32.3%) of 486 fetuses. In 348 cases with a low-risk cfDNA test for common trisomies, NT ≥ 3.5 mm and/or a major structural defect were observed in 92 (26.4%) fetuses. A chromosomal abnormality was found in 17 (18.5%; 95%CI 10.55-26.41) of these pregnancies, including 1 (1.1%) case of trisomy 21 and 16 (17.4%) fetuses with abnormalities different from common trisomies. The respective incidence in the 256 cases with a low-risk cfDNA test result and no ultrasound anomalies was 2.3% (95% CI 0.49-4.20; n = 6).

CONCLUSIONS

In fetuses with first trimester ultrasound anomalies and a low-risk cfDNA result for trisomy 21, 18 and 13, diagnostic testing should be offered with the main objective to detect chromosomal abnormalities beyond common trisomies.

The effect of maternal body mass index and gestational age on circulating trophoblast yield in cell-based noninvasive prenatal testing

OBJECTIVE

To examine the effects of maternal body mass index (BMI) and gestational age (GA) on the number of single circulating trophoblasts (SCT).

METHODS

Maternal blood was collected in 20 to 40 mL. All singleton pregnant women at any gestation were recruited. Trophoblasts were recovered by immunomagnetic enrichment and stained for cytokeratin and CD45. Candidate trophoblasts were identified by fluorescence microscopy.

RESULTS

Blood samples were collected from 425 singleton pregnancies from April 2018 to December 2019. At least one candidate cell was identified in 88% (373/425). There was an inverse correlation between trophoblasts yield and increasing BMI (r = -0.19, P < .001). The mean ± SD number of trophoblasts/mL was 0.12  ± 0.22 in the underweight group (n = 5), 0.23 ± 0.25 in the normal weight (n = 169), 0.18 ± 0.19 in the overweight (n = 114), and 0.13 ± 0.15 in the obese (n = 109). Significantly more cells were identified in the normal weight than those in the obese (P = .001). In addition, the mean ± SD number of cells/mL was 0.21  ± 0.21 at GA of 10 to 14 weeks (n = 260), 0.14 ± 0.23 at GA ≥15 (n = 102) and 0.12 ± 0.12 at GA <10 (n = 63); P < .001.

CONCLUSION

The lower number of SCT was identified from the samples of women with a high BMI. Cell recovery for SCT testing seems optimal at GA of 10 to 14 weeks, but earlier and later testing is still possible.

Advanced maternal age and adverse pregnancy outcomes

A wide range of adverse pregnancy outcomes are associated with women of advanced maternal age (AMA). These include increased risks for miscarriage, chromosomal abnormalities, stillbirth, foetal growth restriction, preterm birth, pre-eclampsia, gestational diabetes mellitus and caesarean section. While a wide body of literature has reported on these risks, varying definitions in both AMA and reported outcomes can make synthesizing the information difficult when counselling an individual women about her specific risks. In this chapter, we discuss the role of AMA on adverse pregnancy outcomes with a view to clarifying the magnitude of the risks for each outcome in the context to enable more informed clinical counselling and decision-making.

Clinical and Economic Evaluation after Adopting Contingent Cell-Free DNA Screening for Fetal Trisomies in South Spain

INTRODUCTION

Contingent cell-free (cf) DNA screening on the basis of the first-trimester combined test (FCT) results has emerged as a cost-effective strategy for screening of trisomy 21 (T21).

OBJECTIVES

To assess performance, patients' uptake, and cost of contingent cfDNA screening and to compare them with those of the established FCT.

METHODS

This is a prospective cohort study including all singleton pregnancies attending to their FCT for screening of T21 at 2 university hospitals in South Spain. When the FCT risk was ≥1:50, there were major fetal malformations, or the nuchal translucency was ≥3.5 mm, women were recommended invasive testing (IT); if the risk was between 1:50 and 1:270, women were recommended cfDNA testing; and for risks bellow 1:270, no further testing was recommended. Detection rate (DR), false-positive rate (FPR), patients' uptake, and associated costs were evaluated.

RESULTS

We analyzed 10,541 women, including 46 T21 cases. DR of our contingent strategy was 89.1% (41/46) at 1.4% (146/10,541) FPR. Uptake of cfDNA testing was 91.2% (340/373), and overall IT rate was 2.0%. The total cost of our strategy was €1,462,895.7, similar to €1,446,525.7 had cfDNA testing not been available.

CONCLUSIONS

Contingent cfDNA screening shows high DR, low IT rate, and high uptake at a similar cost than traditional screening.

A Retrospective Analysis Of Different Contingent Screening Models For Fetal Down Syndrome In Southwestern China

To discuss combinations of traditional screening and noninvasive prenatal screening (NIPS) and to compare which traditional screening is the most suitable first-line screening approach to NIPS, pregnant women were recruited in this retrospective observational study. Pregnant women underwent one of four traditional screening tests. The 9 contingent models were combined by high risk cut-offs of 1:50, 1:100, 1:270 and intermediate risk cut-offs of 1:1000, 1:1500, 1:2000. We analyzed cost and performance of various screening models with contingent screening of different risk cut-offs. Compared with other screening tests, combined first-trimester screening (CFTS) had the lowest proportion of high risk (≥1:270) with the highest detection rate (DR) (78.79%) and the lowest proportion of intermediate risk (1:271~1:1000). When intermediate risk was 1:51 ~1:1500, CFTS as first-line screening had the lowest cost with DR of 93.94%. Other screening tests as the first-line screening with intermediate risk of 1:51~1:1000 had the lowest cost, there DR were 90.91%, 84.62%, 91.67%, respectively. Our study demonstrated if only one traditional screening was allowed to screen pregnant women, CFTS was recommended as the first choice. According to local health and economic conditions, adopting appropriate traditional screening with suitable cut-offs as first-line screening will contributed to a cost-effective screening model.

Assessment of a change of protocol of prenatal screening by inclusion of non-invasive prenatal diagnosis

Objectives

Non-invasive prenatal screening (NIPS) is a test for the detection of major fetal chromosomal abnormalities in maternal blood during pregnancy. The purpose of this study was to assess the performance of NIPS implemented within the framework of the Screening Program for Congenital Abnormalities of the Andalusian Health System.

Methods

A retrospective observational study was undertaken to determine the number of NIPS tests performed since its introduction. The number of invasive diagnostic tests done after the implementation of NIPS in the patients included in the program between March 2016 and August 2017 was also quantified.

Results

A total of 6,258 combined first- and second trimester screening tests were performed, covering 95% of the population. In total, 250 subjects were identified as high risk, of whom 200 underwent NIPS after loss to follow-up. NIPS showed a sensitivity of 100% (95% CI: 76.84-100%) and a specificity of 99.46% (95% CI: 97.04-99.99%).

Conclusions

This test has proven to have a very high sensitivity and specificity. The results obtained demonstrate that the incorporation of NIPS in clinical practice minimizes the rate of miscarriages and reduces the frequency of invasive procedures by 70%.

Diagnosis of major heart defects by routine first-trimester ultrasound examination: association with increased nuchal translucency, tricuspid regurgitation and abnormal flow in ductus venosus

OBJECTIVE

To examine the association between fetal major heart defects and increased nuchal translucency thickness (NT), tricuspid regurgitation and abnormal flow in the ductus venosus in a large population of singleton pregnancies undergoing routine ultrasound examination at 11-13 weeks' gestation.

METHODS

This was a retrospective study of prospectively collected data from singleton pregnancies attending for a routine ultrasound scan at 11-13 weeks' gestation, which included examination of fetal anatomy, measurement of NT and assessment of blood flow across the tricuspid valve and in the ductus venosus, according to a standardized protocol. The incidence of fetal NT ≥ 95^th and ≥ 99^th percentiles, tricuspid regurgitation and reversed a-wave in the ductus venosus in fetuses with and those without a major heart defect was determined and the performance of each marker and their combination in the detection of major heart defects was calculated.

RESULTS

The study population of 93 209 pregnancies with no apparent chromosomal abnormality included 211 (0.23%) with a fetal major heart defect and 92 998 morphologically normal neonates. In 113 (53.6%) cases with a major heart defect, the diagnosis was made at the 11-13-week scan, in 82 (38.9%) at the 18-24-week scan, in 10 (4.7%) at the third-trimester scan and in six (2.8%) postnatally. At the 11-13-week scan, we diagnosed all cases of tricuspid or pulmonary atresia and polyvalvular dysplasia, > 90% of cases of hypoplastic left heart syndrome or atrioventricular septal defect, about 60% of complex heart defects and cases of left atrial isomerism (interrupted inferior vena cava with normal intracardiac anatomy), 30-40% of cases of tetralogy of Fallot and arch abnormalities, 25% of tricuspid valve abnormalities and about 15% of cases of transposition of the great arteries, but none of aortic or pulmonary stenosis or common arterial trunk. Fetal NT ≥ 95^th or ≥ 99^th percentile, tricuspid regurgitation or abnormal ductus venosus flow was observed in 77 (36.5%), 45 (21.3%), 61 (28.9%) and 58 (27.5%) fetuses with a major heart defect, respectively, and in 5678 (6.1%), 857 (0.9%), 1136 (1.2%) and 1644 (1.8%) of those without a heart defect. Any one of NT ≥ 95^th percentile, tricuspid regurgitation or abnormal flow in the ductus venosus was found in 117 (55.5%; 95% CI, 48.5-62.3%) fetuses with a heart defect and in 8166 (8.8%; 95% CI, 8.6-9.0%) of those without a heart defect. Any one of NT ≥ 99^th percentile or the other two markers was found in 99 (46.9%; 95% CI, 40.0-53.9%) fetuses with a heart defect and in 3517 (3.8%; 95% CI, 3.7-3.9%) of those without a heart defect.

CONCLUSION

At 11-13 weeks' gestation, measurement of fetal NT and assessment of flow across the tricuspid valve and in the ductus venosus can lead to early diagnosis of major heart defect. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Should pregnant women be charged for non-invasive prenatal screening? Implications for reproductive autonomy and equal access

The introduction of non-invasive prenatal testing (NIPT) in healthcare systems around the world offers an opportunity to reconsider funding policies for prenatal screening. In some countries with universal access healthcare systems, pregnant women and their partners are asked to (co)pay for NIPT. In this paper, we discuss two important rationales for charging women for NIPT: (1) to prevent increased uptake of NIPT and (2) to promote informed choice. First, given the aim of prenatal screening (reproductive autonomy), high or low uptake rates are not intrinsically desirable or undesirable. Using funding policies to negatively affect uptake, however, is at odds with the aim of screening. Furthermore, copayment disproportionally affects those of lower socioeconomic status, which conflicts with justice requirements and impedes equal access to prenatal screening. Second, we argue that although payment models may influence pregnant women's choice behaviours and perceptions of the relevance of NIPT, the copayment requirement does not necessarily lead to better-informed choices. On the contrary, external (ie, financial) influences on women's personal choices for or against prenatal screening should ideally be avoided. To improve informed decision-making, healthcare systems should instead invest in adequate non-directive, value-focused pretest counselling. This paper concludes that requiring (substantial) copayments for NIPT in universal access healthcare systems fails to promote reproductive autonomy and is unfair.

Noninvasive Prenatal Testing for Trisomies 21, 18, and 13, Sex Chromosome Aneuploidies, and Microdeletions in Average-Risk Pregnancies: A Cost-Effectiveness Analysis

OBJECTIVE

The cost effectiveness of noninvasive prenatal testing (NIPT) has been established for high-risk pregnancies but remains unclear for pregnancies at other risk levels. The aim was to assess the cost effectiveness of NIPT in average-risk pregnancies from the perspective of a provincial public payer in Canada.

METHODS

A model was developed to compare traditional prenatal screening (TPS), NIPT as a second-tier test (performed only after a positive TPS result), and NIPT as a first-tier test (performed instead of TPS) for trisomies 21, 18, and 13; sex chromosome aneuploidies; and microdeletions in a hypothetical annual population cohort of average-risk pregnancies (142 000 to 148,000) in Ontario, Canada. A probabilistic analysis was conducted with 5000 repetitions.

RESULTS

Compared with TPS, NIPT as a second-tier test detected more affected fetuses with trisomies 21, 18, and 13 (188 vs. 158), substantially reduced the number of diagnostic tests (i.e., chorionic villus sampling and amniocentesis) performed (660 vs. 3107), and reduced the cost of prenatal screening ($26.7 million vs. $27.6 million) annually. Compared with second-tier NIPT, first-tier NIPT detected an additional 80 cases of trisomies 21, 18, and 13 at an additional cost of $33 million. The incremental cost per additional affected fetus detected was $412 411. Extending first-tier NIPT to include testing for sex chromosome aneuploidies and 22q11.2 deletion would increase the total screening cost.

CONCLUSIONS

NIPT as a second-tier test is cost-saving compared with TPS alone. Compared with second-tier NIPT, first-tier NIPT detects more cases of chromosomal anomalies but at a substantially higher cost.

Women's choices in non-invasive prenatal testing for aneuploidy screening: results from a single centre prior to introduction in England

OBJECTIVE

To evaluate patient choices and uptake of non-invasive prenatal testing (NIPT) for aneuploidy screening offered in a contingency model as part of routine care.

METHOD

We retrospectively reviewed data for all women with a singleton pregnancy attending for routine first trimester screening over an 18-month period. Women with a 'high-chance' of trisomy 21, 18 or 13 (≥1:150) were offered the choice of no further testing, NIPT or invasive testing, in line with the screening pathway recommended by the UK National Screening Committee.

RESULTS

Of 9342 women attending for a first trimester ultrasound scan, 7939 women were included in this study. Of these, 352 had a high-chance screening result for trisomy 21, and 291 (82.7%) opted for NIPT. The proportion of women opting for NIPT decreased as the chance of trisomy 21 increased: uptake was 93.2%, 90.0%, 77.1% and 47.2% for women with a chance of 1:100-150, 1:50-99, 1:10-49 and >1:10, respectively. 516 women (5.5%) accessed primary NIPT screening in the private sector, and 638 women (6.8%) declined any aneuploidy screening or testing.

CONCLUSION

Implementation of NIPT testing in a contingency model has a high uptake in a non-research National Health Service setting; the rate of uptake is related to the combined test risk result.

Antenatal screening for fetal trisomies using microarray-based cell-free DNA testing: A systematic review and meta-analysis

OBJECTIVE

To evaluate the test accuracy of non-invasive prenatal testing (NIPT) for fetal trisomy 21, 18, and 13 using cell-free (cf) DNA analysis in maternal plasma with microarray quantitation.

METHOD

Systematic review and meta-analysis. Searches in MEDLINE, Pre-MEDLINE, EMBASE, Web of Science, and the Cochrane Library to 09.07.2018.

RESULTS

Five studies analyzing 3074 samples, including 187 trisomy 21, 43 trisomy 18, and 19 trisomy 13 cases, were identified. Risk of bias was high in all studies, introduced particularly by exclusions from analysis and by the role of the sponsor. Sensitivity of microarray-based cfDNA testing was 99.5% (95%CI 96.3%-99.9%) for trisomy 21, 97.7% (95%CI 87.9%-99.6%) for trisomy 18, and 100% (95%CI 83.2%-100%) for trisomy 13. Specificity was 100% (95% CI 99.87%-100%) for trisomy 21, 99.97% (95%CI 99.81%-99.99%) for trisomy 18, and 99.97% (95%CI 99.81%-99.99%) for trisomy 13. Pooled test failure rate was 1.1%. A direct comparison of microarray- and sequencing-based cfDNA found equivalent test accuracy.

CONCLUSION

Included studies suggest that NIPT using microarray-based cfDNA testing has high sensitivity and specificity for detecting fetal trisomy 21, 18, and 13. However, the evidence base is small and at high risk of bias.

Implementation of maternal blood cell-free DNA testing in early screening for aneuploidies

Several externally blinded validation and implementation studies in the last 9 years have shown that it is now possible, through analysis of cell-free (cf) DNA in maternal blood, to effectively detect a high proportion of fetuses affected by trisomies 21, 18, and 13 at a much lower false-positive rate (FPR) than all other existing screening methods. This article is aimed at reviewing technical and clinical considerations for implementing cfDNA testing in routine practice, including methods of analysis, performance of the test, models for clinical implementation, and interpretation of results.

Is there still a role for nuchal translucency measurement in the changing paradigm of first trimester screening?

Objectives

To give an overview of the genetic and structural abnormalities occurring in fetuses with nuchal translucency (NT) measurement exceeding the 95th percentile at first‐trimester screening and to investigate which of these abnormalities would be missed if cell‐free fetal DNA (cfDNA) were used as a first‐tier screening test for chromosomal abnormalities.

Methods

This is a national study including 1901 pregnancies with NT≥95th percentile referred to seven university hospitals in the Netherlands between 1 January 2010 and 1 January 2016. All cases with unknown pregnancy outcome were excluded. Results of detailed ultrasound examinations, karyotyping, genotyping, pregnancy and neonatal outcomes, investigation by a clinical geneticist and post‐mortem investigations were collected.

Results

In total, 821 (43%) pregnancies had at least one abnormality. The rate of abnormalities was 21% for fetuses with NT between 95^th and 99^th percentile and 62% for fetuses with NT≥99^th percentile. Prevalence of single‐gene disorders, submicroscopic, chromosomal and structural abnormalities was 2%, 2%, 30% and 9%, respectively.

Conclusion

Although cfDNA is superior to the combined test, especially for the detection of trisomy 21, 34% of the congenital abnormalities occurring in fetuses with increased NT may remain undetected in the first trimester of pregnancy, unless cfDNA is used in combination with fetal sonographic assessment, including NT measurement.

What's already known about this topic?

Nuchal translucency is associated with a wide range of chromosomal and structural abnormalities.

What does this study add?

If cell‐free DNA were used as the only first trimester screening test, 34% of fetal congenital abnormalities would be missed in the first trimester of pregnancy.

In high‐risk pregnancies with increased nuchal translucency (NT≥95^th percentile), 23% of abnormalities are found in fetuses with NT between 95^th and 99^th percentile.

Targeted capture enrichment followed by NGS: development and validation of a single comprehensive NIPT for chromosomal aneuploidies, microdeletion syndromes and monogenic diseases

BACKGROUND

Non-invasive prenatal testing (NIPT) has been widely adopted for the detection of fetal aneuploidies and microdeletion syndromes, nevertheless, limited clinical utilization has been reported for the non-invasive prenatal screening of monogenic diseases. In this study, we present the development and validation of a single comprehensive NIPT for prenatal screening of chromosomal aneuploidies, microdeletions and 50 autosomal recessive disorders associated with severe or moderate clinical phenotype.

RESULTS

We employed a targeted capture enrichment technology powered by custom TArget Capture Sequences (TACS) and multi-engine bioinformatics analysis pipeline to develop and validate a novel NIPT test. This test was validated using 2033 cell-fee DNA (cfDNA) samples from maternal plasma of pregnant women referred for NIPT and paternal genomic DNA. Additionally, 200 amniotic fluid and CVS samples were used for validation purposes. All NIPT samples were correctly classified exhibiting 100% sensitivity (CI 89.7-100%) and 100% specificity (CI 99.8-100%) for chromosomal aneuploidies and microdeletions. Furthermore, 613 targeted causative mutations, of which 87 were unique, corresponding to 21 monogenic diseases, were identified. For the validation of the assay for prenatal diagnosis purposes, all aneuploidies, microdeletions and point mutations were correctly detected in all 200 amniotic fluid and CVS samples.

CONCLUSIONS

We present a NIPT for aneuploidies, microdeletions, and monogenic disorders. To our knowledge this is the first time that such a comprehensive NIPT is available for clinical implementation.

Creating basis for introducing non‐invasive prenatal testing in the Estonian public health setting

OBJECTIVE

The study aimed to validate a whole-genome sequencing-based NIPT laboratory method and our recently developed NIPTmer aneuploidy detection software with the potential to integrate the pipeline into prenatal clinical care in Estonia.

METHOD

In total, 424 maternal blood samples were included. Analysis pipeline involved cell-free DNA extraction, library preparation and massively parallel sequencing on Illumina platform. Aneuploidies were determined with NIPTmer software, which is based on counting pre-defined per-chromosome sets of unique k-mers from sequencing raw data. SeqFF was implemented to estimate cell-free fetal DNA (cffDNA) fraction.

RESULTS

NIPTmer identified correctly all samples of non-mosaic trisomy 21 (T21, 15/15), T18 (9/9), T13 (4/4) and monosomy X (4/4) cases, with the 100% sensitivity. However, one mosaic T18 remained undetected. Six false-positive (FP) results were observed (FP rate of 1.5%, 6/398), including three for T18 (specificity 99.3%) and three for T13 (specificity 99.3%). The level of cffDNA of <4% was estimated in eight samples, including one sample with T13 and T18. Despite low cffDNA level, these two samples were determined as aneuploid.

CONCLUSION

We believe that the developed NIPT method can successfully be used as a universal primary screening test in combination with ultrasound scan for the first trimester fetal examination.

Nicht invasive Pränataldiagnostik mittels molekulargenetischer Tests (NIPT) zur Erkennung der Trisomien 13, 18 und 21

Hintergrund

Molekulargenetische Tests (NIPT) auf Trisomie sind längst Teil der nicht invasiven Pränataldiagnostik (NIPD). In Deutschland wird derzeit geprüft, ob und für wen diese Tests von den gesetzlichen Krankenkassen künftig bezahlt werden sollen.

Fragestellung

(I) Diagnostische Eigenschaften der NIPT zur Entdeckung der Trisomien 13, 18 und 21 und (II) hypothetische Berechnung der möglichen Anwendung der NIPT in verschiedenen Gruppen.

Methoden

(I) Systematische Recherche nach Primärliteratur und systematischen Übersichten in MEDLINE und vier weiteren Datenbanken. Einschlusskriterien: Studien mit schwangeren Frauen, Indextest: NIPT mittels molekulargenetischer Analyse von cffDNA im mütterlichen Blut zur Bestimmung des Trisomie-Risikos; Referenztest: zytogenetische Diagnostik oder postnatale klinische Untersuchung. (II) Orientierende Recherche. Hypothetische Berechnungen für (1) alle schwangeren Frauen nach aktuellem Vorgehen ohne NIPT am Beispiel von Ersttrimesterscreening (ETS), (2) Anwendung bei schwangeren Frauen mit erhöhtem Risiko, z. B. nach vorgeschaltetem auffälligem ETS und (3) NIPT in einer Population mit und ohne erhöhtes Risiko für eine Trisomie.

Ergebnisse

Bei 22 eingeschlossenen Studien lagen die Sensitivität und die Spezifität zur Erkennung der Trisomie 21 bei 99,13 % (95 %-KI: [97,39 %; 99,72 %]) und 99,95 % (95 %-KI: [99,88 %; 99,98 %]). Der mögliche Einfluss von Testversagern blieb bei den Berechnungen unberücksichtigt, womit die Sensitivität oder die Spezifität der NIPT möglicherweise überschätzt wurde. Für die Erkennung der Trisomien 13 und 18 konnte jeweils die Sensitivität nicht robust geschätzt werden.

Diskussion

Bei Frauen mit erhöhtem Risiko können NIPT die Zahl der invasiven Tests und damit der testbedingten Fehlgeburten vermutlich verringern.

Diagnosis of fetal non-chromosomal abnormalities on routine ultrasound examination at 11-13 weeks' gestation

OBJECTIVE

To examine the performance of the routine 11-13-week scan in detecting fetal non-chromosomal abnormalities.

METHODS

This was a retrospective study of prospectively collected data from 100 997 singleton pregnancies attending for a routine ultrasound examination of fetal anatomy, performed according to a standardized protocol, at 11-13 weeks' gestation. All continuing pregnancies had an additional scan at 18-24 weeks and 71 754 had a scan at either 30-34 or 35-37 weeks. The final diagnosis of fetal abnormality was based on the results of postnatal examination in cases of live birth and on the findings of the last ultrasound examination in cases of pregnancy termination, miscarriage or stillbirth. The performance of the 11-13-week scan in the detection of fetal abnormalities was determined.

RESULTS

The study population contained 1720 (1.7%) pregnancies with a fetal abnormality, including 474 (27.6%) detected on the first-trimester scan, 926 (53.8%) detected on the second-trimester scan and 320 (18.6%) detected in the third trimester or postnatally. At 11-13 weeks' gestation, we diagnosed all cases of acrania, alobar holoprosencephaly, encephalocele, tricuspid or pulmonary atresia, pentalogy of Cantrell, ectopia cordis, exomphalos, gastroschisis and body-stalk anomaly and > 50% of cases of open spina bifida, hypoplastic left heart syndrome, atrioventricular septal defect, complex heart defect, left atrial isomerism (interrupted inferior vena cava with normal intracardiac anatomy), lower urinary tract obstruction, absence of extremities, fetal akinesia deformation sequence and lethal skeletal dysplasia. Common abnormalities that were detected in < 10% of cases at 11-13 weeks included ventriculomegaly, agenesis of the corpus callosum, isolated cleft lip, congenital pulmonary airway malformation, ventricular septal defect, abdominal cysts, unilateral renal agenesis or multicystic kidney, hydronephrosis, duplex kidney, hypospadias and talipes.

CONCLUSIONS

A routine 11-13-week scan, carried out according to a standardized protocol, can identify many severe non-chromosomal fetal abnormalities. A summary statistic of the performance of the first-trimester scan is futile because some abnormalities are always detectable, whereas others are either non-detectable or sometimes detectable. To maximize prenatal detection of abnormalities, additional scans in both the second and third trimesters are necessary. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

New screen on the block: non-invasive prenatal testing for fetal chromosomal abnormalities

Non-invasive prenatal testing (NIPT) is a new screen for fetal chromosomal abnormalities. It is a screening test based on technology that involves the analysis of feto-placental DNA that is present in maternal blood. This DNA is then analysed for abnormalities of specific chromosomes (eg 13, 18, 21, X, Y). NIPT has a much higher screening capability for chromosomal abnormalities than current combined first trimester screening, with ~99% sensitivity for trisomy 21 (Down syndrome) and at least a 10-fold higher positive predictive value. The low false-positive rate (1-3%) is one of the most advertised advantages of NIPT. In practice, this could lead to a significant reduction in the number of false-positive tests and the need for invasive diagnostic procedures. NIPT is now suitable for singleton and twin pregnancies and can be performed from ~10 weeks in a pregnancy. NIPT is not currently publicly funded in most countries. However, the increasing availability of NIPT commercially will likely lead to an increase in demand for this as a screening option. Given the high numbers of women who visit a general practitioner (GP) in their first trimester, GPs are well-placed to also offer NIPT as a screening option. A GP's role in facilitating access to this service will likely be crucial in ensuring equity in access to this technology, and it is important to ensure that they are well supported to do so.

Clinical application of a contingent screening strategy for trisomies with cell-free DNA: a pilot study

BACKGROUND

Different strategies have been designed for clinical implementation of cell-free DNA (cfDNA) testing. We aimed to evaluate the performance of a contingent strategy based on conventional screening and offering cfDNA to the intermediate-risk group, for the screening for trisomies 21, 18 and 13. Secondary objectives were to assess the uptake of cfDNA in women with intermediate-risk, to evaluate the performance of cfDNA testing, and the preferences of pregnant women with intermediate risk.

METHODS

Prospective observational pilot study between February 2016 and March 2017. Singleton pregnancies with a known outcome were included in the study. At the conventional screening (first trimester combined test or second trimester quadruple test) women were classified in high (risk ≥1:250) or low risk (< 1:250). For the study, a contingent strategy was applied: following the conventional screening women were classified into three groups: high risk (risk ≥1:10 or nuchal translucency ≥3 mm), intermediate-risk (risk 1:11 to 1:1500) and low risk (< 1:1500), and a cfDNA test was offered to those at the intermediate risk.

RESULTS

For the analysis, 2639 women were included, 2422 (91.8%) had a first trimester combined test and 217 (8.2%) a second trimester quadruple test. There were 5 cases of trisomy 21, 4 of trisomy 18 and none of trisomy 13. For the contingent strategy, the detection rate and false positive rates were 88.9% (8/9) and 1.3% (35/2630), respectively. For the conventional strategy, the detection rate and false positive rates were 66.7% (6/9) and 5.3% (140/2630), respectively. The cfDNA test had a detection rate for trisomy 21 of 100% (3 out of 3), and a false positive rate of 0.2% (1/466). In a survey, 81.8% (374/457) of women in the intermediate-risk group would choose cfDNA testing as the second line test, mainly due to the lack of risk for the fetus.

CONCLUSION

A contingent screening strategy for trisomies 21, 18 and 13, based on conventional screening, and offering a cfDNA test to women with a risk between 1:11 to 1:1500, reduced the false positive rate and increased the detection rate for these trisomies. Moreover, this strategy is well accepted by women.

No. 348-Joint SOGC-CCMG Guideline: Update on Prenatal Screening for Fetal Aneuploidy, Fetal Anomalies, and Adverse Pregnancy Outcomes

OBJECTIVE

To review the available prenatal screening options in light of the recent technical advances and to provide an update of previous guidelines in the field of prenatal screening.

INTENDED USERS

Health care providers involved in prenatal screening, including general practitioners, obstetricians, midwives, maternal fetal medicine specialists, geneticists, and radiologists.

TARGET POPULATION

All pregnant women receiving counselling and providing informed consent for prenatal screening.

EVIDENCE

Published literature was retrieved through searches of Medline, PubMed, and the Cochrane Library in and prior to March 2016 using an appropriate controlled vocabulary (prenatal diagnosis, amniocentesis, chorionic villi sampling, non-invasive prenatal screening) and key words (prenatal screening, prenatal genetic counselling). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English and published from January 1985 to May 2016. Searches were updated on a regular basis and incorporated in the guideline. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical speciality societies.

GUIDELINE UPDATE

Evidence will be reviewed 5 years after publication to determine whether all or part of the guideline should be updated. However, if important new evidence is published prior to the 5-year cycle, the review process may be accelerated for a more rapid update of some recommendations.

The contingent use of cell-free fetal DNA for prenatal screening of trisomies 21, 18, 13 in pregnant women within a national health service: A budget impact analysis

OBJECTIVE

Non-invasive prenatal testing (NIPT) based on cell-free fetal DNA (cffDNA) is highly accurate in the detection of common fetal autosomal trisomies. Aim of this project was to investigate short-term costs and clinical outcomes of the contingent use of cffDNA for prenatal screening of trisomies 21, 18, 13 within a national health service (NHS).

METHODS

An economic analysis was developed from the perspective of the Italian NHS to compare two possible scenarios for managing pregnant women: women managed according to the Standard of Care screening (SoC) vs a cffDNA scenario, where Harmony Prenatal Test was introduced as a second line screening choice for women with an "at risk" result from SoC screening.

RESULTS

The introduction of cffDNA as a second line screening test, conditional to a risk ≥ 1:1,000 from SoC screening, showed a 3% increase in the detection of trisomies, with a 71% decrease in the number of invasive tests performed. Total short-term costs (pregnancy management until childbirth) decreased by € 19 million (from € 84.5 to 65.5 million).

CONCLUSION

The adoption of the Harmony Prenatal Test in women resulting at risk from SoC screening, implied a greater number of trisomies detection, together with a reduction of the healthcare costs.

First-trimester screening for trisomies by cfDNA testing of maternal blood in singleton and twin pregnancies: factors affecting test failure

OBJECTIVE

To examine factors affecting the rate of failure to obtain a result from cell-free DNA (cfDNA) testing of maternal blood for fetal trisomies 21, 18 and 13 in singleton and twin pregnancies in the first trimester.

METHODS

This was a prospective study of 23 495 singleton and 928 twin pregnancies undergoing screening for fetal trisomy by targeted cfDNA testing at 10 + 0 to 14 + 1 weeks' gestation. Multivariate logistic regression analysis was used to determine significant predictors of failure to obtain a result after first sampling.

RESULTS

There was no result from cfDNA testing after first sampling in 3.4% (798/23 495) of singletons, 11.3% (91/806) of dichorionic twins and 4.9% (6/122) of monochorionic twins. Multivariate logistic regression analysis demonstrated that the risk of test failure, first, increased with increasing maternal age (odds ratio (OR), 1.02; 95% CI, 1.01-1.04) and weight (OR, 1.05; 95% CI, 1.04-1.05), decreasing gestational age (OR, 0.85; 95% CI, 0.79-0.91), serum pregnancy-associated plasma protein-A (PAPP-A) multiples of the median (MoM) (OR, 0.56; 95% CI, 0.49-0.65) and free β-human chorionic gonadotropin (β-hCG) MoM (OR, 0.67; 95% CI, 0.60-0.74), second, was higher in women of black (OR, 1.72; 95% CI, 1.33-2.20) and South Asian (OR, 1.99; 95% CI, 1.56-2.52) than those of white racial origin, in dichorionic twin than in singleton pregnancy (OR, 1.75; 95% CI, 1.34-2.26) and in pregnancies conceived by in-vitro fertilization than in those conceived naturally (OR, 3.82; 95% CI, 3.19-4.55) and, third, was lower in parous than in nulliparous women (OR, 0.63; 95% CI, 0.55-0.74).

CONCLUSIONS

Maternal age, weight, racial origin and parity, gestational age, dichorionicity, method of conception and serum levels of free β-hCG and PAPP-A are independent predictors of cfDNA test failure. The risk of test failure is higher in dichorionic twin than in singleton pregnancies, mainly because a higher proportion of twins are conceived by in-vitro fertilization and more of the women are nulliparous. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Screening for trisomies by cfDNA testing of maternal blood in twin pregnancy: update of The Fetal Medicine Foundation results and meta-analysis

OBJECTIVES

To report on the routine clinical implementation of cell-free DNA (cfDNA) analysis of maternal blood for trisomies 21, 18 and 13 in twin pregnancy and to define the performance of the test by combining our results with those identified in a systematic review of the literature.

METHODS

The data for the prospective study were derived from screening for trisomies 21, 18 and 13 in twin pregnancies at 10 + 0 to 14 + 1 weeks' gestation. Two populations were included; first, self-referred women to the Fetal Medicine Centre in London or Brugmann University Hospital in Brussels and, second, women selected for the cfDNA test after routine first-trimester combined testing at one of two National Health Service hospitals in England. This dataset was used to determine the performance of screening for the three trisomies. Search of MEDLINE, EMBASE, CENTRAL (The Cochrane Library), ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform (ICTRP) was carried out to identify all peer-reviewed publications on clinical validation or implementation of maternal cfDNA testing for trisomies 21, 18 and 13 in twin pregnancy. A meta-analysis was then performed using our data and those in the studies identified by the literature search.

RESULTS

In our dataset of 997 twin pregnancies with a cfDNA result and known outcome, the test classified correctly 16 (94.1%) of the 17 cases of trisomy 21, nine (90.0%) of the 10 cases of trisomy 18, one (50.0%) of the two cases of trisomy 13 and 962 (99.4%) of the 968 cases without any of the three trisomies. The literature search identified seven relevant studies, excluding our previous papers because their data are included in the current study. In the combined populations of our study and the seven studies identified by the literature search, there were 56 trisomy-21 and 3718 non-trisomy-21 twin pregnancies; the pooled weighted detection rate (DR) and false-positive rate (FPR) were 98.2% (95% CI, 83.2-99.8%) and 0.05% (95% CI, 0.01-0.26%), respectively. In the combined total of 18 cases of trisomy 18 and 3143 non-trisomy-18 pregnancies, the pooled weighted DR and FPR were 88.9% (95% CI, 64.8-97.2%) and 0.03% (95% CI, 0.00-0.33%), respectively. For trisomy 13, there were only three affected cases and two (66.7%) of these were detected by the cfDNA test at a FPR of 0.19% (5/2569).

CONCLUSIONS

The performance of cfDNA testing for trisomy 21 in twin pregnancy is similar to that reported in singleton pregnancy and is superior to that of the first-trimester combined test or second-trimester biochemical testing. The number of cases of trisomies 18 and 13 is too small for accurate assessment of the predictive performance of the cfDNA test. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Profile of women choosing the Harmony® Prenatal Test

INTRODUCTION

The Harmony® Prenatal Test, a noninvasive cell-free DNA (cfDNA) method for major trisomies has been available since January 2013 at our unit, and tests were sent to the Ariosa Clinical Laboratory Improvement Amendments (CLIA) laboratory in California. From July 2017 onward, prenatal cfDNA has been reimbursed in Belgium for all pregnancies; however, since then samples are sent to a local laboratory. Little data are available on patient's profile and choices toward cfDNA and on the performance of local technology transfer centers. Areas covered: The profiles and choices of women regarding this test were evaluated. Further, the performance of cfDNA at the local laboratory was compared to the one in California. Our results showed that women from the Netherlands, as compared to Belgium, were more likely to undergo cfDNA testing for maternal request and would be less likely to undergo karyotyping if cfDNA were unavailable, therefore are better candidates for cfDNA testing, when this is used as first-line screening. Expert commentary: Our findings highlight the importance of conducting these types of studies, before decisions about clinical implementation are made by national governments and ministries of health.

Cell-free DNA and contingent screening: Our first year

INTRODUCTION

Analysis of cell-free DNA (cfDNA) from maternal blood has showed a great potential as a screening method for fetal aneuploidies. cfDNA can be used as a first line screening tool or in a contingent model, after the combined test.

METHODS

Prospective study of women attending for first trimester combined screening in our Hospital, in the first year of contingent cfDNA screening. According to the combined screening test result patients were divided in high-risk (offered invasive test or routine follow-up), intermediate-risk (counselled for cfDNA, invasive or routine follow-up) or low-risk (routine ultrasound follow-up). Pregnancy outcomes and performance of screening were evaluated. A cost-effectiveness analysis was also done.

RESULTS

The majority of the 1272 enrolled participants were Caucasian (82,6%), multiparous (51,7%) and the median maternal age was 30 years old. Thirty women screened high-risk and 83,3% of them opted for an invasive test. Forty-nine patients had an intermediate risk and 75,5% of them choose cfDNA testing. Our rate of invasive tests decreased from 3.5% to 2.4%.

DISCUSSION

The cut-offs used to determine high and intermediate-risk are based on a compromise between detection rate, pregnancy lost rate and cost. Above a determined cut-off in the intermediate-risk group, the cost for each additional detected trisomy case is very high. One major benefit of this contingent model was the decrease in invasive testing.

CONCLUSION

The contingent cfDNA screening model can be easily implemented in a public hospital with a low-risk population. Since cost/benefit is an important issue, further studies are needed to determine the ideal cut-off for our country.

The consequences of implementing non-invasive prenatal testing with cell-free foetal DNA for the detection of Down syndrome in the Spanish National Health Service: a cost-effectiveness analysis

BACKGROUND

DNA-based non-invasive prenatal testing (NIPT) using maternal blood constitutes an emerging technology for the detection of Down syndrome (DS). The aim of the study was to conduct a cost-effectiveness analysis to evaluate the economic costs and health implications of the introduction of NIPT based on cell-free foetal DNA analysis through different screening strategies for the detection of DS.

METHODS

An analytical short-term decision model was developed, from the payer´s perspective (Spanish National Health Service). The main outcome measure was the number of DS cases detected. Secondary measures included associated miscarriages, women undergoing current screening, women undergoing NIPT, positive NIPT and invasive procedures performed. The study setting was the Spanish National Health Service. Three strategies were compared: (a) first- and second-trimester screening (current screening); (b) NIPT as contingent testing; and (c) NIPT as first-line testing. Modelling was based on a hypothetical cohort of 100,000 Spanish pregnant women. Population data were obtained from the database of the Basque Antenatal Screening Programme. Deterministic sensitivity analyses were performed to assess variations in the cost of NIPT, screening risk cut-off, screening uptake-rate and rate of failure of NIPT.

RESULTS

NIPT as contingent testing (strategy b) led to fewer miscarriages following invasive procedures and a slight reduction in the number of DS cases detected compared to current screening. However, lowering the screening cut-off to ≥ 1:500 would improve the overall effectiveness of NIPT as contingent testing, increasing the number of DS cases detected and decreasing foetal losses as compared to the current screening, despite there would be an extra-cost of 3.5%. When NIPT was used as first-line testing (strategy c), the screening would be more effective but also more expensive, with incremental cost-effectiveness ratios (ICERs) per additional case of DS detected of €1,299,763 and €1,232,763, compared with strategies a and b, respectively. Results were sensitive to the different parameters considered in the analysis.

CONCLUSIONS

Both, as first-line testing and as contingent testing when screening cut-off was lowered ≥ 1:500, NIPT would lead to more favourable outcomes as compared to the current screening (both in terms of DS cases detected and miscarriages avoided), but at a greater cost.

Routine first-trimester screening for fetal trisomies in twin pregnancy: cell-free DNA test contingent on results from combined test

OBJECTIVE

To report on the routine clinical implementation of cell-free DNA (cfDNA) analysis of maternal blood for trisomies 21, 18 and 13, contingent on the results of the first-trimester combined test in twin pregnancy.

METHODS

Screening for trisomies 21, 18 and 13 was carried out in 959 twin pregnancies by assessment of a combination of maternal age, fetal nuchal translucency thickness, and serum free β-human chorionic gonadotropin and pregnancy-associated plasma protein-A at 11-13 weeks' gestation in two UK NHS hospitals. Women in the high-risk group (risk ≥ 1 in 100) were offered the option of invasive testing, cfDNA testing or no further testing, and those in the intermediate-risk group (risk 1 in 101 to 1 in 2500 in the first phase of the study and 1 in 101 to 1 in 500 in the second phase) were offered cfDNA or no further testing. The trisomic status of the pregnancies was determined by prenatal or postnatal karyotyping or examination of the neonates.

RESULTS

In 42 (4.4%) of the 959 pregnancies, there was termination, miscarriage or stillbirth with no known karyotype or there was loss to follow-up. The 917 pregnancies with known trisomic status of both twins included six that were discordant for trisomy 21, four that were discordant for trisomy 18 and 907 with no trisomy 21, 18 or 13. Following combined screening, 47 (5.1%), 203 (22.1%) and 667 (72.7%) of the pregnancies were classified as high risk, intermediate risk and low risk, respectively. The high-risk group included five (83.3%) cases of trisomy 21 and three (75.0%) of trisomy 18. The cfDNA test was carried out in 224 pregnancies and results were provided in 214 (95.5%); this group included six pregnancies with trisomy 21, three with trisomy 18 and 206 with no trisomy 21, 18 or 13. The cfDNA test classified correctly as screen positive all six cases of trisomy 21 and two of the three with trisomy 18, and as screen negative for each of the trisomies all 206 unaffected pregnancies. Contingent screening led to prenatal detection of all cases of trisomy 21 and three of four with trisomy 18.

CONCLUSION

This study has demonstrated the feasibility of introducing cfDNA testing, contingent on the results of the first-trimester combined test for major trisomies, in a routine population of twin pregnancies. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

A contingent model for cell-free DNA testing to detect fetal aneuploidy after first trimester combined screening

Objective

To assess the results of the first trimester combined test to design a prenatal protocol for the introduction of the cell-free fetal DNA test as a contingent screening model.

Method

An observational retrospective study in 12,327 singleton pregnancies to analyze the results of the combined first trimester screening, the nuchal translucency ≥97.5 percentile, their cytogenetic results and birth outcomes.

Results

A total of 533 (4.3%) pregnant women had a risk in combined first trimester screening above 1/300. In this group, sixty nine had an unbalanced karyotype. The abnormal/normal karyotype ratio was 1/28 in pregnant women with intermediate risk (1/51-1/300) for trisomy 21 and trisomy 18, 1/58 with intermediate risk just for trisomy 21 and 1/37 with intermediate risk just for trisomy 18. A 19.8% of the unbalanced karyotypes had chromosomal abnormalities other than trisomies 21, 18 and 13. Two false negatives cases at first trimester combined screening presented a nuchal translucency ≥ p97.5^th.

Conclusion

We propose the introduction of the cell-free fetal DNA test when the risk of first trimester combined screening is intermediate (1/51–1/300) and when nuchal translucency is ≥ p97.5^th with a low risk in the combined screening. This policy would allow us to continue to detect uncommon chromosomal abnormalities.