Contingent screening for Down syndrome--results from the FaSTER trial

Second-trimester contingent screening for small-for-gestational-age neonate

OBJECTIVES

First, to investigate the additive value of second-trimester placental growth factor (PlGF) for the prediction of a small-for-gestational-age (SGA) neonate. Second, to examine second-trimester contingent screening strategies.

METHODS

This was a prospective observational study in women with singleton pregnancy undergoing routine ultrasound examination at 19-24 weeks' gestation. We used the competing-risks model for prediction of SGA. The parameters for the prior model and the likelihoods for estimated fetal weight (EFW) and uterine artery pulsatility index (UtA-PI) were those presented in previous studies. A folded-plane regression model was fitted in the dataset of this study to describe the likelihood of PlGF. We compared the prediction of screening by maternal risk factors against the prediction provided by a combination of maternal risk factors, EFW, UtA-PI and PlGF. We also examined the additive value of PlGF in a policy that uses maternal risk factors, EFW and UtA-PI.

RESULTS

The study population included 40 241 singleton pregnancies. Overall, the prediction of SGA improved with increasing degree of prematurity, with increasing severity of smallness and in the presence of coexisting pre-eclampsia. The combination of maternal risk factors, EFW, UtA-PI and PlGF improved significantly the prediction provided by maternal risk factors alone for all the examined cut-offs of birth weight and gestational age at delivery. Screening by a combination of maternal risk factors and serum PlGF improved the prediction of SGA when compared to screening by maternal risk factors alone. However, the incremental improvement in prediction was decreased when PlGF was added to screening by a combination of maternal risk factors, EFW and UtA-PI. If first-line screening for a SGA neonate with birth weight < 10^th percentile delivered at < 37 weeks' gestation was by maternal risk factors and EFW, the same detection rate of 90%, at an overall false-positive rate (FPR) of 50%, as that achieved by screening with maternal risk factors, EFW, UtA-PI and PlGF in the whole population can be achieved by reserving measurements of UtA-PI and PlGF for only 80% of the population. Similarly, in screening for a SGA neonate with birth weight < 10^th percentile delivered at < 30 weeks, the same detection rate of 90%, at an overall FPR of 14%, as that achieved by screening with maternal risk factors, EFW, UtA-PI and PlGF in the whole population can be achieved by reserving measurements of UtA-PI and PlGF for only 70% of the population. The additive value of PlGF in reducing the FPR to about 10% with a simultaneous detection rate of 90% for a SGA neonate with birth weight < 3^rd percentile born < 30 weeks, is gained by measuring PlGF in only 50% of the population when first-line screening is by maternal factors, EFW and UtA-PI.

CONCLUSIONS

The combination of maternal risk factors, EFW, UtA-PI and PlGF provides effective second-trimester prediction of SGA. Serum PlGF is useful for predicting a SGA neonate with birth weight < 3^rd percentile born < 30 weeks after an inclusive assessment by maternal risk factors and biophysical markers. Similar detection rates and FPRs can be achieved by application of contingent screening strategies. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Contingent screening in stratification of pregnancy care based on risk of pre-eclampsia at 19-24 weeks' gestation

OBJECTIVE

To explore the possibility of carrying out routine screening for pre-eclampsia (PE) with delivery at < 28, < 32, < 36 weeks' gestation by maternal factors, uterine artery pulsatility index (UtA-PI) and mean arterial pressure (MAP) in all pregnancies and reserving measurements of placental growth factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) for only a subgroup of the population.

METHODS

This was a prospective observational study in two UK maternity hospitals involving women with singleton pregnancy attending for routine assessment at 19-24 weeks' gestation. The improvement in performance of screening for PE, at fixed risk cut-offs, by the addition of serum PlGF and sFlt-1 to screening by maternal factors, UtA-PI and MAP, was estimated. We examined a policy of contingent screening in which biochemical testing was reserved for only a subgroup of the population. The main outcome measures were the additional contribution of PlGF and sFlt-1 to the performance of screening for PE and the proportion of the population requiring measurement of PlGF and sFlt-1 for maximum performance of screening.

RESULTS

The study population included 37 886 singleton pregnancies. At each risk cut-off, the highest detection rates for delivery with PE and the lowest screen-positive rates were achieved in screening with maternal factors, UtA-PI, MAP, PlGF and sFlt-1. The maximum performance by such screening was also achieved by contingent screening in which PlGF and sFlt-1 were measured in only about 40% of the population.

CONCLUSION

The performance of screening for PE by a combination of maternal factors, UtA-PI and MAP is improved by measurement of PlGF and sFlt-1 in about 40% of the population. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

The Knowledge, Attitude, Practices, and Satisfaction of Non-Invasive Prenatal Testing among Chinese Pregnant Women under Different Payment Schemes: A Comparative Study

Non-invasive prenatal testing (NIPT) for aneuploidy screening has been widely applied across China, and costs can affect Chinese pregnant women’s choices. This study aims to assess the knowledge, attitude, practices (KAP) and satisfaction regarding NIPT among pregnant women in China, and to further explore the relationship between payment schemes and women’s acceptability of and satisfaction with NIPT. A questionnaire survey was performed in Shenzhen and Zhengzhou, China, which separately applied “insurance coverage” and “out-of-pocket” payment scheme for NIPT. The major differences between the two cities were compared using chi-square test, Wilcoxon rank sum test, and propensity score matched analysis. Logistic regression models were applied to explore predictors for women’s acceptability and satisfaction. Compared with Zhengzhou participants, a higher proportion of Shenzhen women had heard of NIPT (87.30% vs. 64.03%), were willing to receive NIPT (91.80% vs. 80.43%) and had taken NIPT (83.12% vs. 54.54%), while their satisfaction level was lower. Having NIPT-related knowledge was associated with higher acceptability, and receiving genetic counseling helped to improve satisfaction. Besides, women with higher annual household incomes were more likely to take and be satisfied with NIPT. In conclusion, more attention should be paid to health education, subsidies for NIPT, and genetic counseling.

Prenatal Genetic Testing Options

All patients should be offered prenatal screening and diagnosis. Testing options depend on many factors, including patient age, family history, and patient preference. Options are rapidly changing with emerging technology. Aneuploidy screening options include ultrasound, maternal analytes, and cell-free DNA. Prenatal chromosomal microarray is the recommended diagnostic test for patients with anomalies visualized on prenatal ultrasound. Prenatal whole exome sequencing is clinically available but is limited by challenges with counseling, interpretation, and turn-around time. Future technologies are emerging and may soon allow for translation of prenatal diagnosis to in utero therapy.

Two-stage screening for preterm preeclampsia at 11-13 weeks' gestation

BACKGROUND

Screening for preeclampsia at 11-13 weeks' gestation by a combination of maternal factors, mean arterial pressure, uterine artery pulsatility index, and serum placental growth factor (triple test) can predict about 90% of preeclampsia, with delivery at <32 weeks (early-preeclampsia), and 75% of preeclampsia with delivery at <37 weeks (preterm preeclampsia), at a screen-positive rate of 10%. In pregnancies identified as being at high risk for preeclampsia by such screening, administration of aspirin (150 mg/d from 11 to 14 weeks' gestation to 36 weeks) reduces the rate of early preeclampsia by about 90% and preterm preeclampsia by about 60%. Recording of maternal history and blood pressure are part of routine prenatal care, but measurement of uterine artery pulsatility index and placental growth factor require additional costs.

OBJECTIVE

To explore the possibility of carrying out first-stage screening in the whole population by maternal factors alone or a combination of maternal factors, mean arterial pressure and uterine artery pulsatility index or maternal factors, mean arterial pressure, and placental growth factor and proceeding to second-stage screening by the triple test only for a subgroup of the population selected on the basis of the risk derived from first-stage screening.

STUDY DESIGN

The data for this study were derived from prospective nonintervention screening for preeclampsia at 11⁺⁰ to 13⁺⁶ weeks' gestation in 61,174 singleton pregnancies. Patient-specific risks of delivery with preeclampsia at <37 and <32 weeks' gestation were calculated using the competing risks model to combine the prior distribution of the gestational age at delivery with preeclampsia, obtained from maternal characteristics and medical history, with various combinations of multiple of the median values of mean arterial pressure, uterine artery pulsatility index, and placental growth factor. We estimated the detection rate of preterm-preeclampsia and early-preeclampsia at overall screen-positive rate of 10%, 15%, and 20% from a policy in which first-stage screening of the whole population is carried out by some of the components of the triple test and second-stage screening by the full triple test on women selected on the basis of results from first-stage screening.

RESULTS

If the method of first-stage screening is maternal factors, then measurements of mean arterial pressure, uterine artery pulsatility index, and placental growth factor can be reserved for only 70% of the population, achieving similar detection rate and screen-positive rate as with screening the whole population with the triple test. In the case of first-stage screening by maternal factors, mean arterial pressure, and uterine artery pulsatility index, then measurement of placental growth factor can be reserved for only 30-40% of the population, and if first-stage screening is by maternal factors, mean arterial pressure, and placental growth factor, measurement of uterine artery pulsatility index can be reserved for only 20-30% of the population. Empirical results were consistent with model-based performance.

CONCLUSION

Two-stage screening and biomarker testing for only part of the population will have financial benefits over conducting the test for the entire population.

Have we done our last amniocentesis? Updates on cell-free DNA for Down syndrome screening

Prenatal aneuploidy screening changed significantly in 2012 when cell-free fetal deoxyribonucleic acid (DNA) was introduced as a noninvasive prenatal test. A noninvasive prenatal test detects cell free fragments of fetal DNA from the placenta circulating in maternal blood that coexist with cell-free DNA (cfDNA) of maternal origin. Using next-generation sequencing, the noninvasive prenatal test compares maternal and fetal cfDNA ratios for chromosomes of interest (i.e., 21, 18, 13, X, and Y) to assess chromosomal aneuploidy. Compared to traditional screening using ultrasound and serum markers, the noninvasive prenatal test has superior test characteristics, including a higher detection rate and positive predictive value, and a lower false-positive rate. The noninvasive prenatal test is already used for primary screening in high-risk women and is rapidly expanding to all women. Given its increasing use, understanding the noninvasive prenatal test's limitations is critical. Discordant results (i.e. noninvasive prenatal test is positive for aneuploidy with a normal fetal karyotype) can occur because of biological processes such as aneuploidy confined to the placenta, a vanished twin, maternal aneuploidy or maternal cancer. Use of the noninvasive prenatal test for screening beyond the most common aneuploidies is not recommended. The noninvasive prenatal test is a major advance in prenatal aneuploidy screening but it is not diagnostic and does not replace invasive testing (i.e. chorionic villous sampling or amniocentesis) for confirmation of fetal chromosomal disorders.

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.

Sequential combined test, second trimester maternal serum markers, and circulating fetal cells to select women for invasive prenatal diagnosis

From January 1^st 2013 to August 31^st 2016, 24408 pregnant women received the first trimester Combined test and contingently offered second trimester maternal serum screening to identify those women who would most benefit from invasive prenatal diagnosis (IPD). The screening was based on first trimester cut-offs of ≥1:30 (IPD indicated), 1:31 to 1:899 (second trimester screening indicated) and ≤1:900 (no further action), and a second trimester cut-off of ≥1:250. From January 2014, analysis of fetal cells from peripheral maternal blood was also offered to women with positive screening results. For fetal Down syndrome, the overall detection rate was 96.8% for a false-positive rate of 2.8% resulting in an odds of being affected given a positive result (OAPR) of 1:11, equivalent to a positive predictive value (PPV) of 8.1%. Additional chromosome abnormalities were also identified resulting in an OAPR for any chromosome abnormality of 1:6.6 (PPV 11.9%). For a sub-set of cases with positive contingent test results, FISH analysis of circulating fetal cells in maternal circulation identified 7 abnormal and 39 as normal cases with 100% specificity and 100% sensitivity. We conclude that contingent screening using conventional Combined and second trimester screening tests is effective but can potentially be considerably enhanced through the addition of fetal cell analysis.

Optimal risk cut-offs for Down syndrome contingent maternal serum screening

OBJECTIVES

The objective of this study is to identify the optimal cut-off points of contingent serum screening excluding nuchal translucency (NT) measurement, to categorize the risk level in the first trimester.

METHODS

A prospective database of women undergoing contingent serum screening, without NT measurement, was reviewed. In conventional categorization, the results of first-trimester screening were categorized into high risk (>1:30) (invasive diagnosis was offered); intermediate risk (1:30-1:1500) (second-trimester screening was needed); and low risk (<1:1500) (no further test). We recategorized the risk levels using various upper and lower cut-offs and compared detection rates, false-positive rates, and rates of intermediate risk.

RESULTS

Among 24,874 women, the prevalence of Down syndrome was 1:691. The previously agreed cut-offs had a detection rate of 88.9% and a false-positive rate of 8.5% with high rate of intermediate risk (38.2%). Re-categorization provided the optimal lower and upper cut-offs 1/900 and 1/50, respectively, giving a detection rate of 86.1%, a false-positive rate of 8.1%, and a rate of intermediate risk of 24.8%.

CONCLUSIONS

This is the first study on contingent serum screening without NT measurement which shows a high detection rate with an acceptable false-positive rate. The optimal cut-offs to categorize the risk levels of the upper and the lower cut-off was 1:30-1:50 and 1:900, respectively.

First and second trimester serum tests with and without first trimester ultrasound tests for Down's syndrome screening

BACKGROUND

Down's syndrome occurs when a person has three copies of chromosome 21 (or the specific area of chromosome 21 implicated in causing Down's syndrome) rather than two. It is the commonest congenital cause of mental disability. 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 (i.e. invasive diagnostic testing, and the possibility that a miscarried fetus may be chromosomally normal) and false negative screening tests (i.e. a fetus with Down's syndrome will be missed). 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 and second trimester serum markers with and without first trimester ultrasound markers for the detection of Down's syndrome in the antenatal period, as combinations of markers.

SEARCH METHODS

We conducted a sensitive and comprehensive literature search of 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), the Database of Abstracts of Reviews of Effectiveness (the Cochrane Library 25 August 2011), MEDION (25 August 2011), the Database of Systematic Reviews and Meta-Analyses in Laboratory Medicine (25 August 2011), the National Research Register (Archived 2007), and Health Services Research Projects in Progress database (25 August 2011). We did not apply a diagnostic test search filter. We did forward citation searching in ISI citation indices, Google Scholar and PubMed 'related articles'. We also searched reference lists of retrieved articles SELECTION CRITERIA: Studies evaluating tests of combining first and second trimester maternal serum markers in women up to 24 weeks of gestation for Down's syndrome, with or without first trimester ultrasound markers, 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

Twenty-two studies (reported in 25 publications) involving 228,615 pregnancies (including 1067 with Down's syndrome) were included. Studies were generally high quality, although differential verification was common with invasive testing of only high risk pregnancies. Ten studies made direct comparisons between tests. Thirty-two different test combinations were evaluated formed from combinations of eight different tests and maternal age; first trimester nuchal translucency (NT) and the serum markers AFP, uE3, total hCG, free βhCG, Inhibin A, PAPP-A and ADAM 12. We looked at tests combining first and second trimester markers with or without ultrasound as complete tests, and we also examined stepwise and contingent strategies.Meta-analysis of the six most frequently evaluated test combinations showed that a test strategy involving maternal age and a combination of first trimester NT and PAPP-A, and second trimester total hCG, uE3, AFP and Inhibin A significantly outperformed other test combinations that involved only one serum marker or NT in the first trimester, detecting about nine out of every 10 Down's syndrome pregnancies at a 5% false positive rate. However, the evidence was limited in terms of the number of studies evaluating this strategy, and we therefore cannot recommend one single screening strategy.

AUTHORS' CONCLUSIONS

Tests involving first trimester ultrasound with first and second trimester serum markers in combination with maternal age are significantly better than those without ultrasound, or those evaluating first trimester ultrasound in combination with second trimester serum markers, without first trimester serum markers. We cannot make recommendations about a specific strategy on the basis of the small number of studies available.

Expanding Use of cfDNA Screening in Pregnancy: Current and Emerging Ethical, Legal, and Social Issues

Purpose of Review

In 2011, screening platforms became available in the US that detect and analyze fragments of cell-free placental DNA (cfDNA) in maternal blood serum. Marketed as noninvasive prenatal tests (NIPT), cfDNA screening is more accurate than previously available serum screening tests for certain aneuploidies. The combination of a noninvasive procedure, high specificity and sensitivity, and lower false positive rates for some aneuploidies (most notably Down's syndrome) has led to broad clinician and patient adoption. New ethical, legal, and social issues arise from the increased use and expanded implementation of cfDNA in pregnancy.

Recent Findings

Recently, several professional associations have amended their guidelines on cfDNA, removing language recommending its use in only "high-risk" pregnancies in favor of making cfDNA screening an available option for women with "low-risk" pregnancies as well. At the same time, commercial cfDNA screening laboratories continue to expand the range of available test panels. As a result, the future of prenatal screening will likely include a broader range of genetic tests in a wider range of patients.

Summary

This article addresses the ethical, legal, and social issues related to the shift in guidance and expanded use of cfDNA in pregnant women, including concerns regarding routinized testing, an unmet and increasing demand for genetic counseling services, social and economic disparities in access, impact on groups living with disabling conditions, and provider liability.

Contingent screening for preterm pre-eclampsia

OBJECTIVE

Effective screening for pre-eclampsia resulting in delivery < 37 weeks' gestation (preterm PE) is provided by assessment of a combination of maternal factors, mean arterial pressure (MAP), uterine artery pulsatility index (UtA-PI) and serum placental growth factor (PlGF) at 11-13 or 19-24 weeks' gestation. This study explores the possibility of carrying out routine screening for preterm PE by maternal factors and MAP in all pregnancies and reserving measurements of UtA-PI and PlGF for a subgroup of the population, selected on the basis of the risk derived from screening by maternal factors and MAP alone.

METHODS

Study data were derived from prospective screening for adverse obstetric outcomes in women attending their routine hospital visit at 11-13 and/or 19-24 weeks' gestation. Bayes' theorem was used to derive the a-priori risk for preterm PE from maternal factors and MAP. The posterior risk was obtained by the addition of UtA-PI and PlGF. We estimated the detection rate (DR) of preterm PE, at an overall false-positive rate (FPR) of 10%, from a policy in which first-stage screening by a combination of maternal factors and MAP defines screen-positive, screen-negative and intermediate-risk groups, with the latter undergoing second-stage screening by UtA-PI and PlGF.

RESULTS

At 11-13 weeks' gestation, the model-based DR of preterm PE, at a 10% FPR, when screening the whole population by maternal factors, MAP, UtA-PI and PlGF was 74%. A similar DR was achieved by two-stage screening, with screening by maternal factors and MAP in the first stage and reserving measurement of UtA-PI and PlGF for the second stage and for only 50% of the population. If second-stage screening was offered to 30% of the population, there would be only a small reduction in DR from 74% to 71%. At 19-24 weeks, the model-based DR of preterm PE, at a 10% FPR, when screening the whole population by maternal factors, MAP, UtA-PI and PlGF was 84%. A similar DR was achieved by two-stage screening with measurements of UtA-PI and PlGF in only 70% of the population; if second-stage screening was offered to 40% of the population, the DR would be reduced from 84% to 81%.

CONCLUSIONS

High DR of preterm PE can be achieved by two-stage screening in the first and second trimesters with maternal factors and MAP in the whole population and measurements of UtA-PI and PlGF in only some of the pregnancies. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

How Effective Is First-Trimester Screening for Trisomy 21 Based on Ultrasound Only?

Objective: To evaluate the most common first-trimester ultrasound features of fetuses with trisomy 21 (T21) and to examine the screening performance for Down syndrome (DS) using only ultrasound-based protocols. To investigate whether maternal age (MA) has an impact on the efficacy of the ultrasound-based screening methods. Methods: In a prospective study, 6,265 patients were examined. Two ultrasound-based risk calculation protocols were applied: ‘NT' (based on nuchal translucency) and ‘NT+' (based on NT and secondary markers). Results: A total of 5,696 patients were enrolled for analysis; 84 subjects with T21 were identified. Combinations of abnormal ultrasound markers were observed in only 1.2% of euploid fetuses compared to 71.5% of fetuses with T21. Among 17.9% of DS cases with cardiac anomaly, 14.3% comprised atrioventricular septal defects. For a false-positive rate of 3%, the detection rates of T21 were 73.8 and 91.7% for the ‘NT' and ‘NT+' protocols, respectively. The efficacy of both methods was affected by MA. Conclusions: Most of the fetuses with DS demonstrate a combination of ultrasound markers of aneuploidy in the first trimester. The ‘NT+' protocol is efficient and provides comparable performance as a combined screening test. It is a valuable method, especially when the access to biochemical analysis is restricted.

Comparing outcomes and costs between contingent and combined first-trimester screening strategies for Down's syndrome

OBJECTIVE

To compare a contingent strategy with a combined strategy for prenatal detection of Down's syndrome (DS) in terms of cost, outcomes and safety.

STUDY DESIGN

The contingent strategy was based on a simulation, removing measurement of the free beta subunit of human chorionic gonadotropin (free βhCG) and calculating the DS risk retrospectively in 32,371 pregnant women who had been screened with the combined strategy in the first trimester. In the contingent strategy, a risk between 1:31 and 1:1000 in the first trimester indicated further testing in the second trimester (alpha-fetoprotein, inhibin A, unconjugated oestriol and free βhCG). The cut-off risk values for the contingent and combined strategies in the first trimester were 1:30 and 1:250, respectively, and the cut-off risk value for integrated screening in the second trimester was 1:250. Costs were compared in terms of avoided DS births, and the ratio of loss of healthy fetuses following invasive procedures per avoided DS birth was calculated.

RESULTS

The combined strategy had sensitivity of 40/44 (90.9%) and a false-positive rate of 2.8%. Corresponding values for the contingent strategy were 39/44 (88.6%) and 1.3%, respectively. Only 11% of pregnant women required tests in the second trimester, and the approximate cost reduction for each avoided DS birth was 5000€. The ratio of lost healthy fetuses following invasive procedures per avoided DS birth improved by up to 0.65.

CONCLUSION

The contingent strategy has similar effectiveness to the combined strategy, but has lower costs and fewer invasive procedures.

"Don't Want No Risk and Don't Want No Problems": Public Understandings of the Risks and Benefits of Non-Invasive Prenatal Testing in the United States

BACKGROUND

The recent availability of new non-invasive prenatal genetic tests for fetal aneuploidy has raised questions concerning whether and how these new tests will be integrated into prenatal medical care. Among the many factors to be considered are public understandings and preferences about prenatal testing mechanisms and the prospect of fetal aneuploidy.

METHODS

To address these issues, we conducted a nation-wide mixed-method survey of 2,960 adults in the United States to explore justifications for choices among prenatal testing mechanisms. Open responses were qualitatively coded and grouped by theme.

RESULTS

Respondents cited accuracy, followed by cost, as the most significant aspects of prenatal testing. Acceptance of testing was predicated on differing valuations of knowledge and on personal and religious beliefs. Trust in the medical establishment, attitudes towards risk, and beliefs about health and illness were also considered relevant.

CONCLUSIONS

Although a significant portion of the sample population valued the additional accuracy provided by the new non-invasive tests, they nevertheless expressed concerns over high costs. Furthermore, participants continued to express reservations about the value of prenatal genetic information per se, regardless of how it was obtained.

Cell-free fetal DNA testing for fetal aneuploidy and beyond: clinical integration challenges in the US context

The recent release of new, non-invasive prenatal tests for fetal aneuploidy using cell-free fetal DNA (cffDNA) has been hailed as a revolution in prenatal testing and has triggered significant commercial interest in the field. Ongoing research portends the arrival of a wide range of cffDNA tests. However, it is not yet clear how these tests will be integrated into well-established prenatal testing strategies in the USA, as the timing of such testing and the degree to which new non-invasive tests will supplement or replace existing screening and diagnostic tools remain uncertain. We argue that there is an urgent need for policy-makers, regulators and professional societies to provide guidance on the most efficient and ethical manner for such tests to be introduced into clinical practice in the USA.

Optimal cut-offs for Down syndrome contingent screening in a population of 10,156 pregnant women

STUDY DESIGN

A population of 10,156 pregnant women with singleton pregnancies were screened by the integrated test. Risks were retrospectively recalculated for contingent test strategies with first step intermediate risk groups defined by first trimester upper cut-offs of 1 : 10, 1 : 30, 1 : 50, and 1 : 70 and lower cut-offs 1 : 1500, 1 : 1200, 1 : 1100, and 1 : 900. The second trimester high risk group was based on a single cut-off of 1 : 250.

RESULTS

In the first trimester, the detection rate (DR) ranged from 21% (6/29) to 52% (15/29) as the high risk first trimester cut-off was changed from 1 : 10 to 1 : 70. The corresponding first trimester false positive rate (FPR) increased from 0.2% to 1.4%. In the second trimester, an additional 21/29 (72%) to 12/29 (41%) affected pregnancies could be detected with an additional 1.6% to 2.7% false positives when lower first trimester cut-offs of 1 : 900 to 1 : 1500 were used. The best results were obtained with the upper first trimester cut-off of 1 : 30 and lower first trimester cut-off of 1 : 900, which yielded a rate of women requiring a second trimester test of only 12%, with overall DR and FPR of 93% and 2.8%, respectively.

CONCLUSIONS

Although the study population was relatively small, the results confirm the advantage of using contingent screening and suggest optimal first trimester cut-offs of 1 : 30 (lower cut-off) and 1 : 900 (upper cut-off).

Contingent screening for Down syndrome completed in the first trimester: a multicenter study

OBJECTIVE

To assess a new contingent screening strategy for Down syndrome completed in the first trimester.

METHODS

First-trimester screening combining nuchal translucency thickness measurement and assessment of serum analytes (combined test) was offered to pregnant women who presented for prenatal care during the first trimester to nine health centers and community hospitals in the area served by the Catalan Public Health Service. If an intermediate risk (1/101-1/1000) for Down syndrome was identified, women were referred to the Hospital Clinic Barcelona for risk reassessment that included the use of secondary ultrasound markers (nasal bone, ductus venosus blood flow and tricuspid flow). Intermediate-risk women were divided into two subgroups for further analysis: high-intermediate risk (1/101-1/250) and low-intermediate risk (1/251-1/1000). We compared feasibility and efficacy of both combined and contingent screening strategies.

RESULTS

The combined test, the first screening stage, was performed in 16 001 pregnant women, of whom 1617 (10.1%) were found to have an intermediate risk. Further division of this group showed that 1.8% (n = 289) of women were at high-intermediate risk and 8.3% (n = 1328) at low-intermediate risk. The contingent screening strategy significantly reduced the false-positive rate, from 3.0% to 1.3-1.8% (P < 0.001), without affecting the detection rate (which was 75-79% and 76%, with and without the contingent screening strategy, respectively). However, only 45% of intermediate-risk patients underwent the second screening step due to a preference among high-intermediate-risk (1/101-1/250) women for invasive testing and to low uptake among low-intermediate-risk (1/251-1/1000) women.

CONCLUSIONS

The proposed first-trimester contingent strategy reduces the screen false-positive rate without impacting on the detection rate of Down syndrome. The low compliance observed in our study may prevent its use in certain populations.

Sequential testing for Down syndrome: the impact on estimated risk

OBJECTIVE

Our objective was to describe the utilization of sequential screening and evaluate the impact on estimated Down syndrome risk.

METHODS

We reviewed records of all those undergoing first-trimester screening over a 3-year period. All patients received first-trimester Down syndrome risk, and had options of invasive testing and sequential testing. We compared adjusted first-trimester Down syndrome risk with adjusted risk following sequential testing. Fisher's exact test and chi-square for trend were used for statistical comparison.

RESULTS

First-trimester screening was performed on 12,557 patients. The rate of sequential testing was 34.0%. In 13.1% of patients, sequential testing resulted in a higher risk compared with first-trimester risk, with a risk at least twice as high in 5.2%. The likelihood that sequential testing would increase risk progressively decreased as first-trimester risk declined, from 17.8% for those with first-trimester risk of >1 in 270 to 8.7% in those with first-trimester risk of <1 in 10,000 (p < .001). For those with first-trimester risk <1 in 2000, the likelihood that sequential testing would adjust risk to >1 in 270 was <1%.

CONCLUSIONS

Sequential testing lowers the Down syndrome risk in most cases and is more likely to do so with decreasing first-trimester risk.

Comparison of combined, stepwise sequential, contingent, and integrated screening in 7292 high-risk pregnant women

OBJECTIVE

To compare the efficacy of combined, stepwise sequential, and contingent screening versus the integrated test in detecting fetal aneuploidies.

STUDY DESIGN

First trimester combined test, sequential second trimester, and contingent risks were retrospectively calculated for 7292 unselected pregnant women with singleton pregnancies who had received integrated screening. The first trimester testing was based on nuchal translucency, pregnancy-associated plasma protein-A, and free-beta-human chorionic gonadotrophin (free β-hCG) and the second trimester tests were alpha-fetoprotein, hCG, and unconjugated estriol. A second trimester risk of 1:250 defined a positive result for all protocols with the contingent protocol based on additional second trimester testing for those with risks between 1:30 and 1:1200.

RESULTS

Among the population submitted for the integrated test, the detection rate was 19/21 (90%) for Down syndrome (DS) and 6/6 (100%) for Edwards syndrome (ES) and the DS false-positive rate (FPR) was 247/7271 (3.4%). Provision of the first trimester combined test alone would have resulted in a 17/21 (81%) detection rate for DS, that of 4/6 (67%) for ES and a DS FPR of 292/7271 (4.0%). The sequential and contingent approaches had the same final detection rates as the integrated test but potentially allowed a high proportion of the affected pregnancies to be detected in the first trimester. The lowest net DS FPR was seen with the contingent approach (2.6%) and using this protocol only 12.7% of women would have required second trimester testing.

CONCLUSIONS

Integrated, sequential, and contingent screenings are all more efficacious than the combined test. Overall, the contingent approach was the most efficient with a high-detection rate, the lowest FPR, and the least amount of testing.

Model-predicted performance of second-trimester Down syndrome screening with sonographic prenasal thickness

OBJECTIVE

The purpose of this study was to estimate the Down syndrome detection and false-positive rates for second-trimester sonographic prenasal thickness (PT) measurement alone and in combination with other markers.

METHODS

Multivariate log Gaussian modeling was performed using numerical integration. Parameters for the PT distribution, in multiples of the normal gestation-specific median (MoM), were derived from 105 Down syndrome and 1385 unaffected pregnancies scanned at 14 to 27 weeks. The data included a new series of 25 cases and 535 controls combined with 4 previously published series. The means were estimated by the median and the SDs by the 10th to 90th range divided by 2.563. Parameters for other markers were obtained from the literature.

RESULTS

A log Gaussian model fitted the distribution of PT values well in Down syndrome and unaffected pregnancies. The distribution parameters were as follows: Down syndrome, mean, 1.334 MoM; log(10) SD, 0.0772; unaffected pregnancies, 0.995 and 0.0752, respectively. The model-predicted detection rates for 1%, 3%, and 5% false-positive rates for PT alone were 35%, 51%, and 60%, respectively. The addition of PT to a 4-serum marker protocol increased detection by 14% to 18% compared with serum alone. The simultaneous sonographic measurement of PT and nasal bone length increased detection by 19% to 26%, and with a third sonographic marker, nuchal skin fold, performance was comparable with first-trimester protocols.

CONCLUSIONS

Second-trimester screening with sonographic PT and serum markers is predicted to have a high detection rate, and further sonographic markers could perform comparably with first-trimester screening protocols.

Complete trisomy 21 vs translocation Down syndrome: a comparison of modes of ascertainment

OBJECTIVE

To compare the indications for invasive prenatal testing resulting in the detection of translocation Down syndrome and complete trisomy 21.

STUDY DESIGN

This case control study was based on a large amniocentesis and chorionic villi samples database (n = 534,795). All specimens with translocation Down syndrome (n = 203) comprised the translocation group and were compared with a maternal age-matched group (4 to 1, n = 812) in which complete trisomy 21 was detected. Women with a normal karyotype were randomly selected (n = 812) and served as controls. Indications for invasive testing were compared among the 3 paired groups using χ(2) analysis.

RESULTS

There were no differences in the incidence of abnormal first- and second-trimester screening tests between the translocation Down syndrome and the complete trisomy 21 groups. History of prior aneuploidy was significantly more frequent in the translocation Down syndrome group, as compared with either complete trisomy 21 fetuses or normal controls.

CONCLUSION

Fetuses with translocation Down syndrome present with the same screening abnormalities as fetuses with complete trisomy 21.

Uptake of prenatal diagnostic testing and the effectiveness of prenatal screening for Down syndrome

OBJECTIVES

To map prenatal screening and diagnostic testing pathways in Victorian pregnant women during 2003 to 2004; measure the impact of prenatal diagnostic testing uptake on the effectiveness of prenatal screening for Down syndrome; and assess factors influencing uptake of diagnostic testing following screening.

METHODS

State-wide data collections of prenatal screening and diagnostic tests were linked to all Victorian births and pregnancy terminations for birth defects.

RESULTS

Overall, 52% of women had a prenatal test (65 692/126 305); screening (44.9%), diagnostic testing (3.9%), or both (3.2%). Uptake of diagnostic testing was 71.4% (2390/3349) after an increased risk screen result, and 2.5% (1381/54 286) after a low risk result. Variation in uptake of diagnostic testing reduced the effectiveness of the screening program by 11.2%: from 87.4% (sensitivity - 125/143) to 76.2% (prenatal diagnoses of Down syndrome - 109/143). In both the increased and low risk groups, uptake was influenced by absolute numerical risk, as well as by the change in numerical risk from a priori risk.

CONCLUSIONS

This comprehensive follow-up demonstrates clearly that numerical risk is being used to aid in decision making about confirmatory diagnostic testing. Collectively, these fundamental individual decisions will impact on the overall effectiveness of screening programmes for Down syndrome.

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.

Role of second-trimester genetic sonography after Down syndrome screening

OBJECTIVE

To estimate the effectiveness of second-trimester genetic sonography in modifying Down syndrome screening test results.

METHODS

The First and Second Trimester Evaluation of Risk (FASTER) aneuploidy screening trial participants were studied from 13 centers where a 15- to 23-week genetic sonogram was performed in the same center. Midtrimester Down syndrome risks were estimated for five screening test policies: first-trimester combined, second-trimester quadruple, and testing sequentially by integrated, stepwise, or contingent protocols. The maternal age-specific risk and the screening test risk were modified using likelihood ratios derived from the ultrasound findings. Separate likelihood ratios were obtained for the presence or absence of at least one major fetal structural malformation and for each "soft" sonographic marker statistically significant at the P<.005 level. Detection and false-positive rate were calculated for the genetic sonogram alone and for each test before and after risk modification.

RESULTS

A total of 7,842 pregnancies were studied, including 59 with Down syndrome. Major malformations and 8 of the 18 soft markers evaluated were highly significant. The detection rate for a 5% false-positive rate for the genetic sonogram alone was 69%; the detection rate increased from 81% to 90% with the combined test, from 81% to 90% with the quadruple test, from 93% to 98% with the integrated test, from 97% to 98% with the stepwise test, and from 95% to 97% with the contingent test. The stepwise and contingent use of the genetic sonogram after first-trimester screening both yielded a 90% detection rate.

CONCLUSION

Genetic sonography can increase detection rates substantially for combined and quadruple tests and more modestly for sequential protocols. Substituting sonography for quadruple markers in sequential screening was not useful.

LEVEL OF EVIDENCE

II.

Comparison of modes of ascertainment for mosaic vs complete trisomy 21

OBJECTIVE

We sought to compare the indications for amniocentesis leading to the detection of either mosaicism of trisomy 21 (mosaic-T21) or complete trisomy 21 (T21).

STUDY DESIGN

A retrospective review of a large amniocentesis database (n = 494,163) was conducted. All specimens with mosaic-T21 (n = 124) were compared with a maternal age-matched group of T21 fetuses (n = 496). Samples with normal karyotypes were matched for maternal age and served as normal controls (n = 496). The chi(2) testing was used for statistical analysis.

RESULTS

The presence of an abnormal first-trimester screen, abnormal sonographic findings, and specifically the single sonographic abnormalities of either a cystic hygroma or a cardiac anomaly were significantly less common in the mosaic-T21 as compared with the T21 group. There were no such differences between the mosaic-T21 and the normal control group.

CONCLUSION

Fetuses with mosaic-T21, similar to those with normal karyotype, do not present with the same abnormal screening tests as fetuses with T21.

Correlation between nuchal translucency and nuchal skin-fold measurements in Down syndrome and unaffected fetuses

OBJECTIVE

To assess whether there is a correlation between nuchal translucency (NT) and nuchal skin-fold (NF) measurements, in Down syndrome and in normal pregnancies.

METHODS

Nineteen Down syndrome and 224 normal fetuses underwent ultrasound sequential examinations at 11-13 weeks and 14-28 weeks' gestation. NT was measured at the earlier examination and NF at the later one. Both markers were expressed in multiples of the normal gestation-specific median (MoM). The affected cases had been referred to us for termination of pregnancy; NT had been measured locally and NF was measured at our center prior to the procedure. All unaffected pregnancies were scanned routinely at our center.

RESULTS

There was no statistically significant correlation between NT and NF, in either the Down syndrome (r = 0.076, P = 0.76) or the unaffected (r = - 0.021, P = 0.76) pregnancies. The median NF value in Down syndrome fetuses was 1.538 MoM, compared with 0.990 in unaffected fetuses (P < 0.0001). Gaussian modeling with parameters from a published meta-analysis, updated to include the current series, predicted a 91% detection rate of Down syndrome for a 5% false-positive rate when NF replaced second-trimester biochemistry in a sequential contingent screening strategy.

CONCLUSION

While this study cannot exclude a small correlation between NT and NF, and the Down syndrome karyotype was known at the time of the NF scan, the markers can be considered as independent determinants of Down syndrome risk. Modeling suggests that sequential contingent screening incorporating NF is an effective screening strategy, although this needs to be confirmed in a prospective study.