First trimester combined screening for Trisomy 21 in Hong Kong: outcome of the first 10,000 cases

Impact of replacing or adding placental growth factor on Down syndrome screening: A prospective cohort study

OBJECTIVES

To assess whether adding placental growth factor (PlGF) or replacing pregnancy-associated plasma protein-A (PAPP-A) improves the first trimester combined test performance for trisomy 21.

METHODS

A total of 11,518 women with a singleton pregnancy who underwent the first trimester combined test between December 2016 and December 2019 were included. PlGF was measured and estimated term risk for trisomy 21 was calculated by (1) adding PlGF to the combined test and (2) replacing PAPP-A with PlGF.

RESULTS

Twenty-nine pregnancies had trisomy 21. The combined tests detection rate (DR), false positive rate (FPR) and screen positive rate (SPR) were 89.7%, 5.7% and 6% respectively. DR when adding PlGF to the combined test or replacing PAPP-A remained unchanged. Replacing PAPP-A by PlGF increased FPR and SPR to 6.2% and 6.4% respectively. Adding PlGF to the combined test gave FPR and SPR rates of 5.5% and 5.7% respectively. Change in FPR and SPR was not significant (p > 0.1 for all).

CONCLUSION

Adding PlGF to the combined test or replacing PAPP-A with PlGF did not improve trisomy 21 DR and resulted in a non-significant marginal change in FPR and SPR.

Physicians' perception toward non-invasive prenatal testing through the eye of the Rogers' diffusion of innovation theory in China

OBJECTIVE

Physicians' attitudes and adoption behavior toward the delivery of prenatal tests take vital significance for its influence on their professional practice and patient acceptance. This study aimed to identify how physicians have perceived the diffusion of non-invasive prenatal testing (NIPT) in China.

METHODS

A cross-sectional study was conducted from July 2016 to October 2016 in Shanghai, and Fujian and Sichuan Provinces in China. Physicians working on prenatal screening completed a self-report questionnaire. Following Roger's diffusion of innovation model, multivariable logistic regressions were performed separately for the following key elements of the theory which influence diffusion: physician-perceived attributes of NIPT, communication channels, the nature of the social system, the extent of change agent (who introduces innovations into a society), promotion efforts, and physicians' benefits from adopting NIPT.

RESULTS

Most specialists had a positive attitude (53.2 percent) toward NIPT, whereas 58.9 percent of physicians had already adopted NIPT in their clinical practice. Physician adoption of NIPT was positively associated with the strength of HTA evidence (p = .03), perceived communication frequency with colleagues (p = .04), adoption by other physicians (p = .07), hospital competition (p = .06), hospital teaching status (p = .02), perceived for-profit genetic testing company's promotion (p < .001), and perceived clinical practice skill improvement (p = .02). However, the adoption behavior toward NIPT may be negatively associated with physician-perceived ethical concerns of NIPT (p = .06).

CONCLUSION

Obstetricians and gynecologists' positive perceptions facilitate the adoption of NIPT. Combined with cost-effectiveness analysis of prenatal screening methods, health policy makers can promote the adoption of appropriate, cost-effective prenatal screening in pregnant women.

Performance of prenatal screening using maternal serum and ultrasound markers for Down syndrome in Chinese women: a systematic review and meta-analysis

BACKGROUND

Controversies about the performance of conventional prenatal screening using maternal serum and ultrasound markers (PSMSUM) in detecting Down syndrome (DS) have been raised as a result of a recently available noninvasive prenatal test based on cell-free fetal DNA sequencing.

OBJECTIVES

To evaluate the screening performance of PSMSUM in detecting DS in Chinese women.

SEARCH STRATEGY

An exhaustive literature search of MEDLINE, Embase, the Cochrane Library, ISI Web of Science and China BioMedical Disc.

SELECTION CRITERIA

Primary studies, published from January 2004 to November 2014, which examined the screening accuracy of PSMSUM in pregnant Chinese women, compared with a reference standard, either chromosomal verification or inspection of the newborn.

DATA COLLECTION AND ANALYSIS

Data were extracted as screening positive/negative results for Down and non-Down syndrome pregnancies, allowing estimation of sensitivities and specificities. Risks of bias within and across studies were assessed. Screening accuracy measures were pooled using a bivariate random effects regression model.

MAIN RESULTS

Seventy-eight studies, involving six categories of PSMSUM, were included. Second-trimester double serum [pooled sensitivity (SEN) = 0.80, pooled specificity (SPE) = 0.95] and triple-serum (pooled SEN = 0.79, pooled SPE = 0.96) screening were the predominant PSMSUM methods. The screening performances of these methods achieved the national standard but varied enormously across studies. First-trimester combined screening (pooled SEN = 0.92, pooled SPE = 0.93) and second-trimester quadruple serum screening (median SEN = 0.86, median SPE = 0.96) performed better, but were rarely used.

AUTHOR'S CONCLUSIONS

Second-trimester maternal serum screening has the potential to achieve satisfactory screening performance in middle- and low-income countries. The reported enormous range in screening performance of second-trimester PSMSUM calls for urgent implementation of methods for performance optimization.

TWEETABLE ABSTRACT

Meta-analysis results show good accuracy of maternal serum and ultrasound screening for trisomy 21 in Chinese women.

Prenatal Screening Markers for Down Syndrome: Sensitivity, Specificity, Positive and Negative Expected Value Method

Background

Genetic screening for chromosomopathy is performed in the first trimester of pregnancy by determining fetal nuchal translucency (NT), and the pregnancy associated plasma protein-A (PAPP-A) and free human chorionic gonadotropin (free-beta HCG) biomarkers in maternal serum.

Methods

We tested the sensitivity, specificity, positive and negative expected values of each marker with the aim of setting a model for prenatal screening readings. Statistical data treatment has been performed on a sample of 340 pregnant women with positive results of prenatal screening.

Results

Sensitivity of PAPP-A was 0.6250 (probability 62.50%), free beta HCG 0.5893 (58.93%), NT 0.1785 (17.85%). Specificity of PAPP-A was 0.5106 (probability 51.06%), free beta HCG 0.5246 (52.46%), NT 0.9718 (97.18%). Positive expected value of PAPP-A was 0.2011 (probability 20.11%), free beta HCG 0.1964 (19.64%), NT 0.556 (55.56%). Negative expected value of PAPP-A was 0.8735 (probability 87.35%), free beta HCG 0.8662 (86.62%), NT 0.8571 (85.71%). The NT marker has a significantly higher specificity, which means that its normal value will significantly reduce the final risk of trisomy 21. The sensitivity of NT is much lower than that of biochemical markers, which means that a pathological value of NT does not have a significant influence on the final risk, i.e. the significantly higher sensitivity of biochemical markers will reduce the final risk of trisomy 21.

Conclusions

The analyses stress the importance of using a software which has the possibility to separate the level of a biochemical risk by correlating PAPP-A and free beta HCG and, by adding the NT marker, calculate the level of a final risk of Down syndrome.

First trimester ultrasound tests alone or in combination with first trimester serum tests for Down's syndrome screening

BACKGROUND

Down's syndrome occurs when a person has three, rather than two copies of chromosome 21; or the specific area of chromosome 21 implicated in causing Down's syndrome. It is the commonest congenital cause of mental disability and also leads to numerous metabolic and structural problems. It can be life-threatening, or lead to considerable ill health, although some individuals have only mild problems and can lead relatively normal lives. Having a baby with Down's syndrome is likely to have a significant impact on family life.Non-invasive screening based on biochemical analysis of maternal serum or urine, or fetal ultrasound measurements, allows estimates of the risk of a pregnancy being affected and provides information to guide decisions about definitive testing.Before agreeing to screening tests, parents need to be fully informed about the risks, benefits and possible consequences of such a test. This includes subsequent choices for further tests they may face, and the implications of both false positive and false negative screening tests (i.e. invasive diagnostic testing, and the possibility that a miscarried fetus may be chromosomally normal). The decisions that may be faced by expectant parents inevitably engender a high level of anxiety at all stages of the screening process, and the outcomes of screening can be associated with considerable physical and psychological morbidity. No screening test can predict the severity of problems a person with Down's syndrome will have.

OBJECTIVES

To estimate and compare the accuracy of first trimester ultrasound markers alone, and in combination with first trimester serum tests for the detection of Down's syndrome.

SEARCH METHODS

We carried out extensive literature searches including MEDLINE (1980 to 25 August 2011), Embase (1980 to 25 August 2011), BIOSIS via EDINA (1985 to 25 August 2011), CINAHL via OVID (1982 to 25 August 2011), and The Database of Abstracts of Reviews of Effects (the Cochrane Library 2011, Issue 7). We checked reference lists and published review articles for additional potentially relevant studies.

SELECTION CRITERIA

Studies evaluating tests of first trimester ultrasound screening, alone or in combination with first trimester serum tests (up to 14 weeks' gestation) for Down's syndrome, compared with a reference standard, either chromosomal verification or macroscopic postnatal inspection.

DATA COLLECTION AND ANALYSIS

Data were extracted as test positive/test negative results for Down's and non-Down's pregnancies allowing estimation of detection rates (sensitivity) and false positive rates (1-specificity). We performed quality assessment according to QUADAS criteria. We used hierarchical summary ROC meta-analytical methods to analyse test performance and compare test accuracy. Analysis of studies allowing direct comparison between tests was undertaken. We investigated the impact of maternal age on test performance in subgroup analyses.

MAIN RESULTS

We included 126 studies (152 publications) involving 1,604,040 fetuses (including 8454 Down's syndrome cases). Studies were generally good quality, although differential verification was common with invasive testing of only high-risk pregnancies. Sixty test combinations were evaluated formed from combinations of 11 different ultrasound markers (nuchal translucency (NT), nasal bone, ductus venosus Doppler, maxillary bone length, fetal heart rate, aberrant right subclavian artery, frontomaxillary facial angle, presence of mitral gap, tricuspid regurgitation, tricuspid blood flow and iliac angle 90 degrees); 12 serum tests (inhibin A, alpha-fetoprotein (AFP), free beta human chorionic gonadotrophin (ßhCG), total hCG, pregnancy-associated plasma protein A (PAPP-A), unconjugated oestriol (uE3), disintegrin and metalloprotease 12 (ADAM 12), placental growth factor (PlGF), placental growth hormone (PGH), invasive trophoblast antigen (ITA) (synonymous with hyperglycosylated hCG), growth hormone binding protein (GHBP) and placental protein 13 (PP13)); and maternal age. The most frequently evaluated serum markers in combination with ultrasound markers were PAPP-A and free ßhCG.Comparisons of the 10 most frequently evaluated test strategies showed that a combined NT, PAPP-A, free ßhCG and maternal age test strategy significantly outperformed ultrasound markers alone (with or without maternal age) except nasal bone, detecting about nine out of every 10 Down's syndrome pregnancies at a 5% false positive rate (FPR). In both direct and indirect comparisons, the combined NT, PAPP-A, free ßhCG and maternal age test strategy showed superior diagnostic accuracy to an NT and maternal age test strategy (P < 0.0001). Based on the indirect comparison of all available studies for the two tests, the sensitivity (95% confidence interval) estimated at a 5% FPR for the combined NT, PAPP-A, free ßhCG and maternal age test strategy (69 studies; 1,173,853 fetuses including 6010 with Down's syndrome) was 87% (86 to 89) and for the NT and maternal age test strategy (50 studies; 530,874 fetuses including 2701 Down's syndrome pregnancies) was 71% (66 to 75). Combinations of NT with other ultrasound markers, PAPP-A and free ßhCG were evaluated in one or two studies and showed sensitivities of more than 90% and specificities of more than 95%.High-risk populations (defined before screening was done, mainly due to advanced maternal age of 35 years or more, or previous pregnancies affected with Down's syndrome) showed lower detection rates compared to routine screening populations at a 5% FPR. Women who miscarried in the over 35 group were more likely to have been offered an invasive test to verify a negative screening results, whereas those under 35 were usually not offered invasive testing for a negative screening result. Pregnancy loss in women under 35 therefore leads to under-ascertainment of screening results, potentially missing a proportion of affected pregnancies and affecting test sensitivity. Conversely, for the NT, PAPP-A, free ßhCG and maternal age test strategy, detection rates and false positive rates increased with maternal age in the five studies that provided data separately for the subset of women aged 35 years or more.

AUTHORS' CONCLUSIONS

Test strategies that combine ultrasound markers with serum markers, especially PAPP-A and free ßhCG, and maternal age were significantly better than those involving only ultrasound markers (with or without maternal age) except nasal bone. They detect about nine out of 10 Down's affected pregnancies for a fixed 5% FPR. Although the absence of nasal bone appeared to have a high diagnostic accuracy, only five out of 10 affected Down's pregnancies were detected at a 1% FPR.

Recurrent increased nuchal translucency: a first trimester presentation of familial 13p satellite deletion

Chromosome 13 is one of the acrocentric chromosomes of the human karyotype. Acrocentric chromosomes are the most variable chromosomes in the human karyotype and these variations appear to have no clinical consequences. To the best of our knowledge, this is the first reported case of a first trimester presentation of a 13 short arm satellite deletion with markedly increased nuchal translucency (NT). In this case, the 13p short arm satellite deletion was associated with increased NT in two pregnancies from the same couple.

The assessment of combined first trimester screening in women of advanced maternal age in an Asian cohort

INTRODUCTION

First trimester screening (FTS) is a validated screening tool that has been shown to achieve detection rates of 84%-90% for trisomies 21, 18 and 13. However, its effectiveness for different maternal ages has not been assessed. The present study aimed to assess the performance of FTS in an Asian population, and to compare its effectiveness in older (≥ 35 years) and younger (< 35 years) women. The potential use of noninvasive prenatal test (NIPT) as a contingent screening test is also examined.

METHODS

Data on cases of FTS performed on singleton pregnancies over a six-year period was collated from two Singapore maternal centres, National University Hospital and Singapore General Hospital. Cases that had a 1:250 risk of trisomy were considered to be screen-positive. Pregnancy outcomes were obtained from birth records or karyotype test results.

RESULTS

From 10,289 FTS cases, we obtained a sensitivity of 87.8%, a specificity of 97.6%, a false positive rate of 2.4% and a false negative rate of 0.06% for the detection of aneuploidy. The overall detection rate for trisomy 21 was 86.5%-85.7% for older women and 87.5% for younger women. The mean number of invasive tests required per case of trisomy 21 was 9.3 in younger women, 8.6 in older women and 13.5 in women with intermediate risk (1:250-1,000).

CONCLUSION

While the performance of FTS was similar in younger and older women, more invasive procedures were required to diagnose trisomy 21 in women with intermediate risk. It may be advantageous to offer contingent NIPT to this group of women to reduce the risk of iatrogenic fetal loss.

Non-invasive prenatal testing: ethics and policy considerations

New technologies analyzing fetal DNA in maternal blood have led to the wide commercial availability of non-invasive prenatal testing (NIPT). We present here for clinicians the ethical and policy issues related to an emerging practice option. Although NIPT presents opportunities for pregnant women, particularly women who are at increased risk of having a baby with an abnormality or who are otherwise likely to access invasive prenatal testing, NIPT brings significant ethics and policy challenges. The ethical issues include multiple aspects of informed decision-making, such as access to counselling about the possible results of the test in advance of making a decision about participation in NIPT. Policy considerations include issues related to offering and promoting a privately available medical strategy in publicly funded institutions. Ethics and policy considerations merge in NIPT with regard to sex selection and support for persons living with disabilities.

Ten Years of Experience with First-Trimester Screening for Fetal Aneuploidy Employing Biochemistry from Gestational Weeks 6+0 to 13+6

Objectives: To validate the performance of first-trimester screening for fetal aneuploidy employing blood samples drawn in gestational weeks 6-13. Methods: Prospective combined first-trimester screening for fetal aneuploidy in Denmark was validated in two large datasets: (1) a dataset from the Central Denmark Region including 147,768 pregnancies from October 2003 to October 2013, and (2) a national dataset including 220,739 pregnancies from January 2008 to August 2011. Results: For trisomy 21, the weekly median multiple of the median (MoM) increased from 0.37 in week 6 to 0.70 in week 13 (pregnancy-associated plasma protein-A), and from 0.99 in week 6 to 2.68 in week 13 (free βhCG). The overall detection rate (DR) for fetal trisomy 21 was 91.2%. Employing blood samples from gestational week 9, the DR was 97% (p = 0.05). For fetal trisomy 18, trisomy 13 and triploidy, the overall DRs after first-trimester screening were 79.5, 86 and 85%. In the national dataset, the overall DR for trisomy 21 was 86.3% ranging from 89 (weeks 9 and 10) to 80% (weeks 12 and 13). Conclusion: The results from both datasets show that blood sampling in gestational weeks 9-10 is a robust and high-performance strategy, which can be applied for routine first-trimester screening in clinical practice.

Diagnostic accuracy of the BACs-on-Beads™ assay versus karyotyping for prenatal detection of chromosomal abnormalities: a retrospective consecutive case series

OBJECTIVE

To evaluate the diagnostic performance of the BACs-on-Beads(™) (BoBs(™)) assay for prenatal detection of chromosomal abnormalities.

DESIGN

Retrospective study.

SETTING

Tertiary prenatal diagnosis centre.

POPULATION

Women referred for prenatal diagnosis.

METHODS

We retrieved 2153 archived DNA samples collected between January 2010 and August 2011 for the BoBs(™) assay. These samples had previously been tested by quantitative fluorescence polymerase chain reaction (QF-PCR) and karyotyping. In the BoBs(™) assay a sample was defined as normal disomic when the ratio of the fluorescence intensities in a chromosome locus lay within the threshold (mean ratio ± 2SD), and as deleted or duplicated when the ratio was below the lower threshold (0.6-0.8) or above the upper threshold (1.3-1.4), respectively. The BoBs(™) results were further validated by microarray and compared in a blinded manner with the original QF-PCR and karyotyping results.

MAIN OUTCOME MEASURES

Concordance of any numerical, structural, and submicroscopic chromosomal abnormalities between the methods.

RESULTS

BACs-on-Beads(™) was similar to karyotyping and QF-PCR in detecting trisomy 13, trisomy 18, trisomy 21, and sex chromosomal aneuploidies, and superior to QF-PCR in detecting major structural abnormalities (53.3 versus 13.3%) and mosaicism (28.6 versus 0%) involving chromosomal abnormalities other than the common aneuploidies. BoBs(™) detected six microdeletion syndromes missed by karyotyping and QF-PCR; however, BoBs(™) missed two cases of triploidy identified by QF-PCR. Therefore, the sensitivity of BoBs(™) is 96.7% (95% CI 92.6-98.7%), and its specificity is 100% (95% CI 99.8-100%).

CONCLUSIONS

BACs-on-Beads(™) can replace QF-PCR for triaging in prenatal diagnosis, and gives a better diagnostic yield than current rapid aneuploidy tests.

Clinical utility of noninvasive fetal trisomy (NIFTY) test--early experience

Objective: To report the initial experience of noninvasive prenatal diagnosis of fetal Down syndrome (The NIFTY test) in a clinical setting. Methods: The NIFTY test was offered as a screening test for fetal Down syndrome to pregnant women with a singleton pregnancy at 12 weeks of gestation or beyond. A satisfaction questionnaire was sent to the first 400 patients. Results: During a 6-month period, 567 NIFTY tests were performed. Over 90% of those studied were ethnic Chinese, and the mean age of the women studied was 36 years. The test was performed at 12–13 weeks of gestation in 49.21%. The median reporting time was 9 days. The test was positive for trisomy 21 in eight cases, and for trisomy 18 in 1 case; all were confirmed by fetal karyotyping. There was no false-positive result. Of the questionnaires, 182 completed responses were received. Over 95% had complete or almost complete resolution of anxiety. Except for one, all were satisfied with the NIFTY test, and all indicated that they would recommend the test to their friends. Conclusion: The NIFTY test was a highly specific test. Unnecessary invasive tests and associated fetal losses could be avoided in almost all women who have a normal fetus.

Effect of image settings on nuchal translucency thickness measurement by a semi-automated system

OBJECTIVE

To investigate whether pre- and post-processing image settings affect NT measurements made by a semi-automatic method (SAM).

METHODS

Different image settings (e.g. gain) were either adjusted one at a time on images that had been obtained during fetal NT scans (post-processing, n = 66), or adjusted one at a time during live scanning and image acquisition of the adult posterior tibial artery (pre-processing group, n = 91). The NT and luminal diameter of the posterior tibial artery, respectively, were measured by SAM on all original and adjusted images.

RESULTS

Alteration of the image settings resulted in a statistically significant effect on the measurements taken by SAM, with an average pair difference ranging from 0.001 mm to 0.139 mm. Most of the differences were small and therefore the clinical impact would be negligible. The pair differences were greatest with a very high contrast setting, or without tissue harmonic imaging (THI); the paired difference in measurement in those with vs those without THI was more than 0.1 mm in over 40% of cases.

CONCLUSIONS

Measurements made by SAM are affected by image settings.

Identification of submicroscopic chromosomal aberrations in fetuses with increased nuchal translucency and apparently normal karyotype

OBJECTIVE

Fetal nuchal translucency (NT) is assessed by ultrasonography as a screening tool for aneuploidy at 11 to 13 + 6 weeks' gestation. Fetuses with increased NT but apparently normal karyotype are still at higher risk of structural abnormality and a range of genetic syndromes, which may be related to major and submicroscopic chromosomal abnormalities. The aim of this study was to report the prevalence of submicroscopic chromosomal abnormalities in a cohort of apparently euploid fetuses that presented with increased NT.

METHODS

DNA was extracted from stored chorionic villus samples from fetuses found to have increased NT (> 3.5 mm) during first-trimester screening. These samples were examined by microarray-based comparative genomic hybridization (aCGH) using a 44K oligonucleotide array specifically constructed for prenatal screening. Variations in copy number (CNVs) were reported after excluding known non-pathogenic variants and after validation with multiplex ligation-dependent probe amplification (MLPA) or real-time quantitative polymerase chain reaction (qPCR). The prevalence of pathogenic CNVs is reported and the association with NT and other ultrasound findings described.

RESULTS

CNVs were reported in 6/48 (12.5%) cases by aCGH and the microdeletions or microduplications ranged from 1.1 to 7.9 Mb. Five of these were validated by MLPA/real-time qPCR and four (8.3%) were considered to be pathogenic and clinically significant. The incidence of pathogenic CNVs was 20.0% (2/10) among those cases with other sonographic anomalies and 5.3% (2/38) among those without.

CONCLUSION

aCGH allows detection of submicroscopic chromosomal abnormalities, the prevalence of which may be increased in fetuses with NT > 3.5 mm and an apparently normal karyotype.

Fetal nuchal translucency thickness in different cut-off points for aneuploidy screening in the south of Vietnam

AIMS

The purpose of this study was to define the most suitable cut-off point for fetal nuchal translucency thickness in a screening program for aneuploidy and trisomy 21 in the south of Vietnam.

MATERIAL & METHODS

Two thousand and five hundred cases of singleton pregnancies were followed prospectively from the first trimester to the delivery. The rate of aneuploidy was calculated by seeking a relationship to increased fetal nuchal translucency thickness then calculating the sensitivity and specificity of different cut-off points in thickness measurement to find the most suitable point for screening.

RESULTS

The prevalence of fetal abnormality was 1.5% (95% CI 1.1-2.1), and 1.2% (95% CI 0.8-1.7) of aneuploidy cases found and the commonest was trisomy 21. A cut-off point at 2.4 mm showed the highest level of sensitivity and specificity for the detection of aneuploidy (65.5 and 95.7%) and trisomy 21 (75.0 and 95.1%), with a false-positive rate of 4.3 and 4.9%, respectively.

CONCLUSION

Using a cut-off point of nuchal translucency at 2.4 mm has potential for aneuploidy and trisomy 21 screening in the south of Vietnam.

Comparison of likelihood ratios of first-trimester nuchal translucency measurements: multiples of median, delta or mixture

OBJECTIVE

To compare the likelihood ratios (LR) determined for a measured nuchal translucency (NT) using the multiples of the median (MoM), delta-NT and mixture model approaches.

METHODS

This was a retrospective study of singleton pregnancies with known outcome screened at the 12(th) week of pregnancy between January 2006 and May 2008. NT, crown-rump length (CRL) and LR for trisomy 21 using the delta-NT approach (LRNT-delta) were extracted from The Fetal Medicine Foundation trisomy 21 risk-calculation software database. NT measurements were converted into their equivalent MoM by dividing by the expected CRL-specific median NT. LR for trisomy 21 based on the MoM (LRNT-MoM) of each case was then calculated as the ratio of the Gaussian probability density functions using published trisomy 21 risk-screening parameters. The LR using the mixture model (LRNT-mixture) was calculated as the ratio of individual composite probability densities reported for trisomy 21 and unaffected pregnancies. The intraclass correlation coefficient (ICC) was used to assess the agreement between the three different approaches while the paired t-test was used to perform pairwise comparisons.

RESULTS

Of the 5907 pregnancies with known outcome, 14 had trisomy 21. The ICC between the three approaches to determining an LR was 0.947 (95% CI, 0.943-0.951; P < 0.0001). Pairwise comparison indicated that differences between LR were statistically significant (P < 0.0001). Likelihood ratios determined via the delta-NT model were in general greater than those produced by both the mixture model (z = 5.58, P < 0.0001) and the MoM approaches (z = 32.8, P < 0.0001). For a 5% false-positive rate the detection rate of trisomy 21 (DR) was 78.6% (95% CI, 57.1-99.9%) The screen positive thresholds to achieve this DR were 1 : 200 for the delta-NT approach, 1 : 220 for the mixture approach and 1 : 290 for the MoM approach.

CONCLUSION

No single method of determining NT-associated LR outperformed the others in its ability to detect a trisomy 21-affected pregnancy.

Comparison of first-trimester contingent screening strategies for Down syndrome

OBJECTIVE

To assess the relative performance of a multi-stage first-trimester screening protocol for fetal Down syndrome.

METHODS

Data from 10,767 women who underwent combined ultrasound and biochemistry (BC) screening in the first trimester were reanalyzed using a contingent model approach. Amongst the 10,854 fetuses with known outcome, 32 had Down syndrome, 232 had other abnormalities and 10,590 were unaffected. Nuchal translucency (NT), BC and combined (NT-BC) gestational age-specific risks were calculated for each individual using The Fetal Medicine Foundation risk calculation algorithms (Mixture Model and Biochemistry). Individual patients were categorized as at low, high or intermediate risk according to one of the following three strategies. In 'Strategy-NT-BC' initial screening was performed using both NT and BC. In 'Strategy-BC' initial screening was undertaken using maternal serum markers followed by NT assessment in those with an intermediate risk (1 : 51 < risk <or= 1:1000) while in 'Strategy-NT' initial screening was undertaken using NT followed by serum marker assessment in those with an intermediate risk (1 : 51 < risk <or= 1:1000). The nasal bone was assessed in those with an intermediate risk as the final stage in each of the three strategies. Those with an adjusted risk of 1 in 100 or higher after nasal bone assessment were reclassified as high risk. Detection and false-positive rates were compared between differing strategies in our local population, and this analysis was also performed with the maternal age for our population standardized to the distribution found in England and Wales.

RESULTS

In our local population the detection rate for a 5% false-positive rate using a combined screening policy (NT-BC) was 88% (95% CI, 75.3-98.9%), and 2.3% had an absent nasal bone. The respective detection rate and false-positive rate of the three multi-stage screening strategies were: Strategy-NT-BC: 87.5 and 2.5%; Strategy-BC: 87.5 and 5%; Strategy-NT: 84.4 and 2.9%. In the contingent Strategy-BC only 29% of those initially screened using serum markers required an NT scan. If the model were applied to a hypothetical obstetric population standardized to the maternal age distribution in England and Wales, the detection and false-positive rates of the same three screening strategies would be: Strategy-NT-BC: 86.2 and 1.9%; Strategy-BC: 82.8 and 4%; Strategy-NT: 75.8 and 2.3%, respectively.

CONCLUSION

First-trimester contingent screening provides detection and false-positive rates comparable to those achieved using combined screening, but could be used to significantly reduce the number of scans performed.

Non-invasive prenatal detection of fetal trisomy 18 by RNA-SNP allelic ratio analysis using maternal plasma SERPINB2 mRNA: a feasibility study

OBJECTIVE

Non-invasive prenatal diagnosis of chromosome aneuploidies has been achieved by measuring the ratio of two alleles of a single nucleotide polymorphism (SNP) in circulating placental mRNA (the RNA-SNP allelic ratio approach) in maternal plasma. We investigated the feasibility of applying this approach for the non-invasive prenatal detection of fetal trisomy 18.

METHOD

We targeted serpin peptidase inhibitor, clade B (ovalbumin), membrane 2 (SERPINB2) mRNA, which is transcribed from chromosome 18 and is preferentially expressed by the placenta. We developed a mass-spectrometric assay to measure the SERPINB2 RNA-SNP allelic ratios in the placental samples and maternal plasma obtained from pregnancies involving euploid and trisomy 18 fetuses.

RESULTS

We were able to separate all the euploid and trisomy 18 placentas by their SERPINB2 RNA-SNP allelic ratios. The allelic ratios of the trisomy 18 placentas deviated from the reference interval established from the euploid placentas. Due to the relatively low concentrations of SERPINB2 mRNA in maternal plasma, we used pooled maternal plasma samples for analysis. We were able to identify three of the four pooled trisomy 18 plasma samples by their deviated allelic ratios when compared with the reference interval obtained from pooled euploid plasma samples.

CONCLUSION

It is feasible to detect fetal trisomy 18 non-invasively by maternal plasma SERPINB2 RNA-SNP analysis provided that sufficient quantities of plasma samples are used.