SURUSS in perspective

Ethnic-specific reference range affects the efficacy of quadruple test as a universal screening for Down syndrome in a developing country

Objective

To evaluate the efficacy of the quadruple test for potential use as a Thai national policy for Down syndrome (DS) screening and establish an accurate equation for risk estimation of Down syndrome based on gestational age, weight and the ethnic-specific reference range of our population.

Methods

A prospective study was conducted on singleton pregnancies at 14 to 21 weeks of gestation to evaluate the efficacy of quadruple DS screening using the automatically calculated Western European descent factor (WF) in our population and the impact of screening using a specific Thai ethnic factor as well as to establish an equation for the risk estimation of DS based on gestational age, weight and a local Thai ethnic factor to correct for the impact of ethnic factor on the screening efficacy.

Results

Of a total of 5,515 women, 12 cases of DS and 8 cases of other aneuploidies were found. The detection rate, false positive rate and specificity were 75.0%, 9.1% and 90.9%, respectively, by automatic calculation with the widely used WF; the screening efficacy was lower when used in Asian populations than in other studies. The best-fitted regression equation of serum quadruple screening of AFP, free β-hCG, uE3 and inhibin A was established by adjustment for gestational age (GA) in days, maternal weight and our Thai-specific ethnic reference range which was created for this study. Calculations with our Thai-specific ethnic model gave a better detection rate of 83.3%, a false positive rate of 9.6% and specificity of 90.4%.

Conclusion

The serum quadruple test had a lower detection rate than expected when the risk estimation was based on the WF reference range. The serum quadruple test using WF had significantly different levels when corrected with our ethnic-specific factor. Using our local ethnic specific model could increase the detection rate of DS screening in Thailand with a minimal increase in false positive rates. Our findings indicate that DS screening should be adjusted with an appropriate individual ethnic factor when used for national screening.

Obstetrical provider knowledge and attitudes towards cell-free DNA screening: results of a cross-sectional national survey

Background

Cell-free DNA (cfDNA) screening has recently acquired tremendous attention, promising patients and healthcare providers a more accurate prenatal screen for aneuploidy than other current screening modalities. It is unclear how much knowledge regarding cfDNA screening obstetrical providers possess which has important implications for the quality and content of the informed consent patients receive.

Methods

A survey was designed to assess obstetrical provider knowledge and attitudes towards cfDNA screening and distributed online through the Society of Obstetricians & Gynecologists of Canada (SOGC). Chi-squared tests were used to detect differences in knowledge and attitudes between groups.

Results

207 respondents completed the survey, composed of 60.6% Obstetricians/Gynecologists (OB/GYN), 15.4% Maternal Fetal Medicine (MFM) specialists, 16.5% General Practitioners (GP), and 7.5% Midwives (MW). MFM demonstrated a significant trend of being most knowledgeable about cfDNA screening followed by OB/GYN, GP, and lastly MW in almost all aspects of cfDNA screening. All groups demonstrated an overall positive attitude towards cfDNA screening; however, OB/GYN and MFM demonstrated a significantly more positive attitude than GP and MW. Despite not yet being a diagnostic test, 19.4% of GP would offer termination of pregnancy immediately following a positive cfDNA screen result compared to none of the MFM and only few OB/GYN or MW.

Conclusions

We have demonstrated that different types of obstetrical providers possess varying amounts of knowledge regarding cfDNA screening with MFM currently having greater knowledge to all other groups. All obstetrical providers must have adequate prenatal screening understanding so that we can embrace the benefits of this novel and promising technology while protecting the integrity of the informed consent process.

Electronic supplementary material

The online version of this article (10.1186/s12884-018-1662-z) contains supplementary material, which is available to authorized users.

Genomics-based non-invasive prenatal testing for detection of fetal chromosomal aneuploidy in pregnant women

BACKGROUND

Common fetal aneuploidies include Down syndrome (trisomy 21 or T21), Edward syndrome (trisomy 18 or T18), Patau syndrome (trisomy 13 or T13), Turner syndrome (45,X), Klinefelter syndrome (47,XXY), Triple X syndrome (47,XXX) and 47,XYY syndrome (47,XYY). Prenatal screening for fetal aneuploidies is standard care in many countries, but current biochemical and ultrasound tests have high false negative and false positive rates. The discovery of fetal circulating cell-free DNA (ccfDNA) in maternal blood offers the potential for genomics-based non-invasive prenatal testing (gNIPT) as a more accurate screening method. Two approaches used for gNIPT are massively parallel shotgun sequencing (MPSS) and targeted massively parallel sequencing (TMPS).

OBJECTIVES

To evaluate and compare the diagnostic accuracy of MPSS and TMPS for gNIPT as a first-tier test in unselected populations of pregnant women undergoing aneuploidy screening or as a second-tier test in pregnant women considered to be high risk after first-tier screening for common fetal aneuploidies. The gNIPT results were confirmed by a reference standard such as fetal karyotype or neonatal clinical examination.

SEARCH METHODS

We searched 13 databases (including MEDLINE, Embase and Web of Science) from 1 January 2007 to 12 July 2016 without any language, search filter or publication type restrictions. We also screened reference lists of relevant full-text articles, websites of private prenatal diagnosis companies and conference abstracts.

SELECTION CRITERIA

Studies could include pregnant women of any age, ethnicity and gestational age with singleton or multifetal pregnancy. The women must have had a screening test for fetal aneuploidy by MPSS or TMPS and a reference standard such as fetal karyotype or medical records from birth.

DATA COLLECTION AND ANALYSIS

Two review authors independently carried out study selection, data extraction and quality assessment (using the QUADAS-2 tool). Where possible, hierarchical models or simpler alternatives were used for meta-analysis.

MAIN RESULTS

Sixty-five studies of 86,139 pregnant women (3141 aneuploids and 82,998 euploids) were included. No study was judged to be at low risk of bias across the four domains of the QUADAS-2 tool but applicability concerns were generally low. Of the 65 studies, 42 enrolled pregnant women at high risk, five recruited an unselected population and 18 recruited cohorts with a mix of prior risk of fetal aneuploidy. Among the 65 studies, 44 evaluated MPSS and 21 evaluated TMPS; of these, five studies also compared gNIPT with a traditional screening test (biochemical, ultrasound or both). Forty-six out of 65 studies (71%) reported gNIPT assay failure rate, which ranged between 0% and 25% for MPSS, and between 0.8% and 7.5% for TMPS.In the population of unselected pregnant women, MPSS was evaluated by only one study; the study assessed T21, T18 and T13. TMPS was assessed for T21 in four studies involving unselected cohorts; three of the studies also assessed T18 and 13. In pooled analyses (88 T21 cases, 22 T18 cases, eight T13 cases and 20,649 unaffected pregnancies (non T21, T18 and T13)), the clinical sensitivity (95% confidence interval (CI)) of TMPS was 99.2% (78.2% to 100%), 90.9% (70.0% to 97.7%) and 65.1% (9.16% to 97.2%) for T21, T18 and T13, respectively. The corresponding clinical specificity was above 99.9% for T21, T18 and T13.In high-risk populations, MPSS was assessed for T21, T18, T13 and 45,X in 30, 28, 20 and 12 studies, respectively. In pooled analyses (1048 T21 cases, 332 T18 cases, 128 T13 cases and 15,797 unaffected pregnancies), the clinical sensitivity (95% confidence interval (CI)) of MPSS was 99.7% (98.0% to 100%), 97.8% (92.5% to 99.4%), 95.8% (86.1% to 98.9%) and 91.7% (78.3% to 97.1%) for T21, T18, T13 and 45,X, respectively. The corresponding clinical specificities (95% CI) were 99.9% (99.8% to 100%), 99.9% (99.8% to 100%), 99.8% (99.8% to 99.9%) and 99.6% (98.9% to 99.8%). In this risk group, TMPS was assessed for T21, T18, T13 and 45,X in six, five, two and four studies. In pooled analyses (246 T21 cases, 112 T18 cases, 20 T13 cases and 4282 unaffected pregnancies), the clinical sensitivity (95% CI) of TMPS was 99.2% (96.8% to 99.8%), 98.2% (93.1% to 99.6%), 100% (83.9% to 100%) and 92.4% (84.1% to 96.5%) for T21, T18, T13 and 45,X respectively. The clinical specificities were above 100% for T21, T18 and T13 and 99.8% (98.3% to 100%) for 45,X. Indirect comparisons of MPSS and TMPS for T21, T18 and 45,X showed no statistical difference in clinical sensitivity, clinical specificity or both. Due to limited data, comparative meta-analysis of MPSS and TMPS was not possible for T13.We were unable to perform meta-analyses of gNIPT for 47,XXX, 47,XXY and 47,XYY because there were very few or no studies in one or more risk groups.

AUTHORS' CONCLUSIONS

These results show that MPSS and TMPS perform similarly in terms of clinical sensitivity and specificity for the detection of fetal T31, T18, T13 and sex chromosome aneuploidy (SCA). However, no study compared the two approaches head-to-head in the same cohort of patients. The accuracy of gNIPT as a prenatal screening test has been mainly evaluated as a second-tier screening test to identify pregnancies at very low risk of fetal aneuploidies (T21, T18 and T13), thus avoiding invasive procedures. Genomics-based non-invasive prenatal testing methods appear to be sensitive and highly specific for detection of fetal trisomies 21, 18 and 13 in high-risk populations. There is paucity of data on the accuracy of gNIPT as a first-tier aneuploidy screening test in a population of unselected pregnant women. With respect to the replacement of invasive tests, the performance of gNIPT observed in this review is not sufficient to replace current invasive diagnostic tests.We conclude that given the current data on the performance of gNIPT, invasive fetal karyotyping is still the required diagnostic approach to confirm the presence of a chromosomal abnormality prior to making irreversible decisions relative to the pregnancy outcome. However, most of the gNIPT studies were prone to bias, especially in terms of the selection of participants.

Down Syndrome Screening in India: Are We There Yet?

Down syndrome is the most common cause of intellectual disability among live born children and is amenable to prenatal detection. Screening for Down syndrome on a population basis requires a thorough understanding of the principles involved in the screening tests. We discuss the rationale behind the commonly available screening tests and the Indian scenario in this setting.

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.

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.

Combined screening test for trisomy 21 - is it as efficient as we believe?

OBJECTIVES

To compare two first-trimester screening strategies: traditional combined screening and the one based on ultrasound markers only. We investigated the effect of maternal age (MA) on the screening performance of both of these strategies.

METHODS

This was a prospective observational study based on a non-selected mixed-risk population of 11,653 women referred for first-trimester screening. The study population was divided in two groups: combined screening (CS) and ultrasound-based screening (US). Absolute risk was calculated to determine the influence of MA on screening performance.

RESULTS

The CS arm comprised 5145 subjects including 51 cases of trisomy 21 (T21), and the US arm comprised 5733 subjects including 87 subjects with T21. Seven hundred and seventy-five subjects were excluded from the study. For a false positive rate (FPR) of 3%, the detection rate (DR) of T21 in CS arm was 78% vs. 90% in US arm. For 5% FPR, DR was 84% and 94% in CS and US arm, respectively. MA had an influence on DR positive rates in CS: both DR and FPR for T21 increased with advance in MA.

CONCLUSIONS

The US protocol showed higher DR of T21 compared to the CS one. It may be considered as a viable alternative to CS for T21 where access to biochemical testing is limited.

Screening for chromosomal abnormalities using combined test in the first trimester of pregnancy

Objective

This study was designed to review the screening performance of combined test at the Ewha Womans University Mokdong hospital.

Methods

All women admitted for routine antenatal care between January 1st 2008 and December 31st 2012 with a known pregnancy outcome were included in this study, totaling 1,156 women with singleton pregnancies presenting at 10 to 13 weeks of gestation. Women were offered screening using a combination of maternal serum pregnancy-associated plasma protein-A, free β-human chorionic gonadotropin and fetal nuchal translucency thickness. Those with an estimated risk of ≥1 in 250 of carrying a fetus with trisomy 21 or ≥1 in 300 risk of trisomy 18 were offered genetic counseling with the option of an invasive diagnostic test.

Results

The median of gestational age was 11+3 weeks, the median of crown-rump length was 47.1 mm, and the median age of the women was 31 years. The detection rate was 80% for trisomy 21 (4 of 5) and 100% for trisomy 13 and 18 (all 2). The false-positive rate was 7.73% for trisomy 21 and 1.21% for trisomy 18.

Conclusion

This study was the first large population study performed with the aim of analyzing the performance of the combined test in Korea. This study demonstrated that the detection rates and other figures of the first trimester combined test are comparable to the results reported in other papers worldwide. Consequently, if strict conditions for good screening outcomes are achieved, the first trimester combined test might well be the earliest detectable screening, improving detection rates without increasing karyotyping or economic and other implications that inevitably ensue.

Urine 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 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. The risk of a Down's syndrome affected pregnancy increases with advancing maternal age.Noninvasive 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 and second trimester urine markers for the detection of Down's syndrome.

SEARCH METHODS

We carried out 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 2011, Issue 7), MEDION (25 August 2011), The Database of Systematic Reviews and Meta-Analyses in Laboratory Medicine (25 August 2011), The National Research Register (archived 2007), Health Services Research Projects in Progress database (25 August 2011). We studied reference lists and published review articles.

SELECTION CRITERIA

Studies evaluating tests of maternal urine in women up to 24 weeks of gestation for Down's syndrome, compared with a reference standard, either chromosomal verification or macroscopic postnatal inspection.

DATA COLLECTION AND ANALYSIS

We extracted data as test positive or 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 (Quality Assessment of Diagnostic Accuracy Studies) criteria. We used hierarchical summary ROC (receiver operating characteristic) meta-analytical methods to analyse test performance and compare test accuracy. We performed analysis of studies allowing direct comparison between tests. We investigated the impact of maternal age on test performance in subgroup analyses.

MAIN RESULTS

We included 19 studies involving 18,013 pregnancies (including 527 with Down's syndrome). Studies were generally of high quality, although differential verification was common with invasive testing of only high-risk pregnancies. Twenty-four test combinations were evaluated formed from combinations of the following seven different markers with and without maternal age: AFP (alpha-fetoprotein), ITA (invasive trophoblast antigen), ß-core fragment, free ßhCG (beta human chorionic gonadotrophin), total hCG, oestriol, gonadotropin peptide and various marker ratios. The strategies evaluated included three double tests and seven single tests in combination with maternal age, and one triple test, two double tests and 11 single tests without maternal age. Twelve of the 19 studies only evaluated the performance of a single test strategy while the remaining seven evaluated at least two test strategies. Two marker combinations were evaluated in more than four studies; second trimester ß-core fragment (six studies), and second trimester ß-core fragment with maternal age (five studies).In direct test comparisons, for a 5% false positive rate (FPR), the diagnostic accuracy of the double marker second trimester ß-core fragment and oestriol with maternal age test combination was significantly better (ratio of diagnostic odds ratio (RDOR): 2.2 (95% confidence interval (CI) 1.1 to 4.5), P = 0.02) (summary sensitivity of 73% (CI 57 to 85) at a cut-point of 5% FPR) than that of the single marker test strategy of second trimester ß-core fragment and maternal age (summary sensitivity of 56% (CI 45 to 66) at a cut-point of 5% FPR), but was not significantly better (RDOR: 1.5 (0.8 to 2.8), P = 0.21) than that of the second trimester ß-core fragment to oestriol ratio and maternal age test strategy (summary sensitivity of 71% (CI 51 to 86) at a cut-point of 5% FPR).

AUTHORS' CONCLUSIONS

Tests involving second trimester ß-core fragment and oestriol with maternal age are significantly more sensitive than the single marker second trimester ß-core fragment and maternal age, however, there were few studies. There is a paucity of evidence available to support the use of urine testing for Down's syndrome screening in clinical practice where alternatives are available.

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.Noninvasive 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. However, no test can predict the severity of problems a person with Down's syndrome will have.

OBJECTIVES

The aim of this review was to estimate and compare the accuracy of first trimester serum markers for the detection of Down's syndrome in the antenatal period, both as individual markers and as combinations of markers. Accuracy is described by the proportion of fetuses with Down's syndrome detected by screening before birth (sensitivity or detection rate) and the proportion of women with a low risk (normal) screening test result who subsequently had a baby unaffected by Down's syndrome (specificity).

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), Health Services Research Projects in Progress database (25 August 2011). We did forward citation searching ISI citation indices, Google Scholar and PubMed 'related articles'. We did not apply a diagnostic test search filter. We also searched reference lists and published review articles.  

SELECTION CRITERIA

We included studies in which all women from a given population had one or more index test(s) compared to a reference standard (either chromosomal verification or macroscopic postnatal inspection). Both consecutive series and diagnostic case-control study designs were included. Randomised trials where individuals were randomised to different screening strategies and all verified using a reference standard were also eligible for inclusion. Studies in which test strategies were compared head-to-head either in the same women, or between randomised groups were identified for inclusion in separate comparisons of test strategies. We excluded studies if they included less than five Down's syndrome cases, or more than 20% of participants were not followed up.

DATA COLLECTION AND ANALYSIS

We extracted data as test positive or 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 (Quality Assessment of Diagnostic Accuracy Studies) criteria. We used hierarchical summary ROC meta-analytical methods or random-effects logistic regression methods to analyse test performance and compare test accuracy as appropriate. Analyses of studies allowing direct and indirect comparisons between tests were undertaken.

MAIN RESULTS

We included 56 studies (reported in 68 publications) involving 204,759 pregnancies (including 2113 with Down's syndrome). Studies were generally of good quality, although differential verification was common with invasive testing of only high-risk pregnancies. We evaluated 78 test combinations formed from combinations of 18 different tests, with or without maternal age; ADAM12 (a disintegrin and metalloprotease), AFP (alpha-fetoprotein), inhibin, PAPP-A (pregnancy-associated plasma protein A, ITA (invasive trophoblast antigen), free βhCG (beta human chorionic gonadotrophin), PlGF (placental growth factor), SP1 (Schwangerschafts protein 1), total hCG, progesterone, uE3 (unconjugated oestriol), GHBP (growth hormone binding protein), PGH (placental growth hormone), hyperglycosylated hCG, ProMBP (proform of eosinophil major basic protein), hPL (human placental lactogen), (free αhCG, and free ßhCG to AFP ratio. Direct comparisons between two or more tests were made in 27 studies.Meta-analysis of the nine best performing or frequently evaluated test combinations showed that a test strategy involving maternal age and a double marker combination of PAPP-A and free ßhCG significantly outperformed the individual markers (with or without maternal age) detecting about seven out of every 10 Down's syndrome pregnancies at a 5% false positive rate (FPR). Limited evidence suggested that marker combinations involving PAPP-A may be more sensitive than those without PAPP-A.

AUTHORS' CONCLUSIONS

Tests involving two markers in combination with maternal age, specifically PAPP-A, free βhCG and maternal age are significantly better than those involving single markers with and without age. They detect seven out of 10 Down's affected pregnancies for a fixed 5% FPR. The addition of further markers (triple tests) has not been shown to be statistically superior; the studies included are small with limited power to detect a difference.The screening blood tests themselves have no adverse effects for the woman, over and above the risks of a routine blood test. However some women who have a 'high risk' screening test result, and are given amniocentesis or chorionic villus sampling (CVS) have a risk of miscarrying a baby unaffected by Down's. Parents will need to weigh up this risk when deciding whether or not to have an amniocentesis or CVS following a 'high risk' screening test result.

Prenatal screening: perspective for the pediatrician

Pediatricians are the first contact of a child with genetic disorders such as Down Syndrome. After diagnosis, parents often express and wish that if it was possible to detect it during pregnancy and could it be avoided in the future pregnancy. This makes it essential that pediatricians should have some idea about the basic screening methods and strategy used during pregnancy.

Epitope analysis and detection of human chorionic gonadotropin (hCG) variants by monoclonal antibodies and mass spectrometry

Human chorionic gonadotropin (hCG) is an important marker for pregnancy, pregnancy-related disorders, and various cancers. Different molecular forms of hCG occur in different clinical conditions, and these can be distinguished with immunoassays using well-characterized monoclonal antibodies. Exact knowledge of the epitopes of the antibodies used is crucial for the design of assays with desired specificity. The epitopes of many hCG antibodies have been determined by comparing their reactivity with six 1st International Reference Reagents (IRRs) for hCG, but the specificity of some antibodies remains to be exactly defined. We have therefore studied the reactivity of 30 monoclonal antibodies (mAbs) with the six 1st IRRs for hCG, and variants were investigated using immunoaffinity extraction combined with liquid chromatography-mass spectrometry (LC-MS/MS) for the detection of hCG variants by specific tryptic signature peptides. Each of the mAbs had previously been characterized with regard to epitope specificity in the 2nd Tissue Differentiation Workshop on hCG of the International Society of Oncology and BioMarkers (ISOBM). Simultaneous identification of different hCG variants by LC-MS/MS confirmed that two standards used for mAb characterization, nicked hCG (hCGn, 1st IRR 99/642) and nicked β subunit of hCG (hCGβn, 1st IRR 99/692), are heterogeneous, being composed of two major variants each: hCGn44/45 and hCGn47/48 as well as hCGβn44/45 and hCGβ47/48. Furthermore, MS revealed cross-contamination by non-nicked hCG of the 1st IRR hCGn (99/642) standard. This information enabled fine-tuning of the previous epitope classifications of mAbs specific for heterodimeric hCG (c-mAbs). LC-MS/MS confirmed that c2-mAbs and most c1-mAbs did not recognize hCGn as the observed response in radioimmunoassays obviously resulted from the contamination of hCGn with hCG. Thus, c1 and c2 epitopes are partially dependent on hCGβ peptide loop 2. c3-mAbs recognized both hCG and hCGn. It appeared that c-mAbs cannot discriminate between hCGn44/45 and hCGn47/48 as they either recognize both or neither variant. For most mAbs directed against hCGβ, epitope specificity determined by LC-MS/MS was highly concordant with that obtained using standard immunological methods. In analogy to c-mAbs, hCGβ-mAbs cannot discern between hCGβn44/45, hCGβn47/48, or intact hCGβ as all 15 mAbs recognizing hCGβ also recognized both nicked variants irrespective of which of the three major hCGβ antigenic domains their epitopes were located within: on the caps of peptide loops 1 and 3, around the cystine knot, or along the hCGβCTP. LC-MS/MS confirmed that their epitopes were not located on hCGβ peptide loop 2. Thus, LC-MS/MS provided in-depth information on hCG variant composition of hCGn (99/642) and hCGβn (99/692) and hCG variant specificity profiles and facilitated precise classification of the epitopes of anti-hCG mAbs. This has impact on the design of selective immunoassays.

The associations of nuchal translucency and fetal abnormalities; significance and implications

This review of literature describes the first-trimester nuchal translucency (NT) which forms the basis of new form of screening which can lead to a significant improvement in detection of congenital anomalies as compared to second trimester screening programs, the so called genetic-sonogram. A growing body of evidence-based studies has demonstrated that fetal NT can be a powerful prenatal screening tool and combined with first trimester serum markers, it can be incredibly promising in near future. It should be expressed as Multiple of median (MoM) and maintained and monitored like any laboratory analyte. The aim of this review was to investigate the different hypotheses on the aetiology of increased NT. Using a computerized database (PubMed), articles on the aetiology of first-trimester NT were retrieved. Furthermore, the cited references of the retrieved articles were used to find additional articles. Based on ultrasonography, the associations of increased NT fetuses are described in relation with Down syndrome, Cardiac anomalies, and a diverse range of other anomalies. The review concludes that first trimester NT ultrasound has the potential to be used as an important tool for the detection of various congenital abnormalities and an early management can be implemented to reduce the mental trauma of expecting mothers by proper counseling and early diagnosis. For the precise measurements, it should be implemented in a meticulous and coherent manner.

Second trimester serum 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 retardation. Noninvasive 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.  

OBJECTIVES

To estimate and compare the accuracy of second trimester serum markers for the detection of Down's syndrome.

SEARCH METHODS

We carried out a sensitive and comprehensive literature search of MEDLINE (1980 to May 2007), EMBASE (1980 to 18 May 2007), BIOSIS via EDINA (1985 to 18 May 2007), CINAHL via OVID (1982 to 18 May 2007), The Database of Abstracts of Reviews of Effectiveness (The Cochrane Library 2007, Issue 1), MEDION (May 2007), The Database of Systematic Reviews and Meta-Analyses in Laboratory Medicine (May 2007), The National Research Register (May 2007), Health Services Research Projects in Progress database (May 2007). We studied reference lists and published review articles.  

SELECTION CRITERIA

Studies evaluating tests of maternal serum in women at 14-24 weeks of 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

Fifty-nine studies involving 341,261 pregnancies (including 1,994 with Down's syndrome) were included. Studies were generally high quality, although differential verification was common with invasive testing of only high-risk pregnancies. Seventeen studies made direct comparisons between tests. Fifty-four test combinations were evaluated formed from combinations of 12 different tests and maternal age; alpha-fetoprotein (AFP), unconjugated oestriol (uE3), total human chorionic gonadotrophin (hCG), free beta human chorionic gonadotrophin (βhCG), free alpha human chorionic gonadotrophin (αhCG), Inhibin A, SP2, CA125, troponin, pregnancy-associated plasma protein A (PAPP-A), placental growth factor (PGF) and proform of eosinophil major basic protein (ProMBP).Meta-analysis of 12 best performing or frequently evaluated test combinations showed double and triple tests (involving AFP, uE3, total hCG, free βhCG) significantly outperform individual markers, detecting six to seven out of every 10 Down's syndrome pregnancies at a 5% false positive rate. Tests additionally involving inhibin performed best (eight out of every 10 Down's syndrome pregnancies) but were not shown to be significantly better than standard triple tests in direct comparisons. Significantly lower sensitivity occurred in women over the age of 35 years. 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 the accuracy of the sensitivity.

AUTHORS' CONCLUSIONS

Tests involving two or more markers in combination with maternal age are significantly more sensitive than those involving one marker. The value of combining four or more tests or including inhibin have not been proven to show statistically significant improvement. Further study is required to investigate reduced test performance in women aged over 35 and the impact of differential pregnancy loss on study findings.

Performance of first-trimester combined test for Down syndrome in different maternal age groups: reason for adjustments in screening policy?

OBJECTIVE

To evaluate the performance of the first-trimester combined test (FCT) in different maternal age groups and to discuss whether adjustments in screening policies should be made.

METHODS

In this retrospective study data (n = 26 274) from a fetal medicine center on FCT (maternal age, fetal NT, free β-human chorionic gonadotrophin, pregnancy-associated plasma protein-A) were studied.

RESULTS

70.6% of cases was <36 years and 43% of the Down syndrome (DS) cases were detected in this age group. For women <36 years and advanced maternal age (AMA) women (≥36 years) detection rate (DR) and false positive rate (FPR) were 94.5% and 4.1%, and 95.8% and 13.0%, respectively (cut-off 1:200). Lowering the cut-off showed an improved balance in DR and FPR. With increasing maternal age FPR and DR increased and odds of being affected given a positive result (OAPR) decreased.

CONCLUSION

FCT is effective in women <36 and ≥36 years. The balance between FPR and DR is more favourable in women <36 years with comparable OAPR. Although FPR increases with increasing maternal age, performance of FCT in AMA women is more effective than screening based on maternal age alone. Lowering the cut-off to 1:100 in AMA women is suggested to improve screening performance. Routinely offering diagnostic testing to AMA women as a screening policy for the detection of DS seems not reasonable.

Performance characteristics of the UniCel DxI 800 immunoassay for the maternal serum quadruple test, including median values for each week of gestation, in Korean women

BACKGROUND

Maternal serum prenatal quadruple screening includes testing for alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG), unconjugated estriol (uE3), and dimeric inhibin A (DIA). We evaluated quadruple screening using an automated platform and looked for any ethnic differences in the median values of each marker.

METHODS

We measured the concentrations of each quadruple test analyte using the UniCel DxI 800 system (Beckman Coulter, USA) in 788 Korean mid-trimester maternal serum samples and calculated their median values using Benetech software (Benetech, Canada). We also compared the results with those obtained using the Immulite 2000 assay (Siemens Healthcare Diagnostics, USA) or ELISA (DSL, USA) in 442 samples.

RESULTS

We obtained mid-trimester median values for each marker. The following are the comparative results for each test using the Immulite 2000 assay or ELISA (x) and the UniCel DxI 800 immunoassay (y): AFP, y=1.10x+0.01, r=0.925; uE3, y=0.28x+0.24, r=0.885; hCG, y=1.22x-3047.8, r=0.944; and DIA, y=0.86x+15.31, r=0.833. Assay results for each of the four markers showed good correlations. However, significant biases necessitated new median calculations of prenatal risk estimates in all four tests.

CONCLUSIONS

We established gestational age-specific second-trimester median values for four markers in Korean samples using the UniCel DxI 800 immunoassay system. Despite significant bias, there were good correlations between the results obtained using the UniCel DxI 800 immunoassay and those obtained using the Immulite 2000 assay.

Antenatal screening and informed choice: a cross-sectional survey of parents and professionals

BACKGROUND

antenatal screening for fetal abnormalities is now offered to all pregnant women in many countries in Europe. Previous studies have shown that women and their partners may not make informed choices about screening.

OBJECTIVES

to investigate knowledge of screening in both prospective parents and professionals offering screening in England, and to identify the ways in which pregnant women and their partners could be supported to make informed decisions about antenatal screening.

DESIGN

cross-sectional survey design. Data were collected from July 2007 to January 2008 using two self-completion questionnaires.

SETTING AND PARTICIPANTS

questionnaires were completed by: (i) pregnant women (n=100) and their partners (n=11), and (ii) midwives involved in offering antenatal screening (n=78).

MEASUREMENTS

demographic data and survey responses were analysed using descriptive statistics and cross-tabulations.

FINDINGS

some midwives lack accurate knowledge about screening and the conditions for which screening is offered. Parents wish to have information about screening at an earlier stage and would like the prospective father to be included in screening discussions. There is evidence that many parents do not perceive the second trimester ultrasound scan as a method of screening. Balanced information about the lives of people with Down syndrome would be seen as helpful by many parents.

KEY CONCLUSIONS

further efforts need to be made to educate midwives more fully so that pregnant women and their partners are able to make informed choices about screening. Balanced information about the lives of people with Down syndrome should be available to prospective parents to support their decision making.

[Prenatal serum marker screening in Korea: survey results]

BACKGROUND

Maternal serum triple marker screening has been covered by the medical insurance system in Korea since December 2004. The number of tests is on the increase, but an external quality control program and a basic survey have not been established yet. The aim of this study was to port the survey of prenatal screening tests.

METHODS

Three different quality control specimens were prepared using the sera obtained from 100 women who were in the 15th to 20th week of pregnancy and visited Asan Medical Center during May 2005. We assumed that the three specimens belonged to the first day of 15 weeks, third day of 16 weeks, and second day of 19 weeks, respectively, and sent them to 10 laboratories. Nine laboratories replied to the survey. We analyzed concentrations, multiples of medians (MoMs), and risk estimates.

RESULTS

The coefficients of variance of MoM were 32.1-32.6% for alpha-fetoprotein, 15.3-19.8% for unconjugated estriol, 6.3-12.5% for human chorionic gonadotropin, and 12.9-18.2% for inhibin-A. In Down syndrome risk estimation for specimen-2, six of the eight laboratories that used the triple test reported the screen positive, but two laboratories reported negative. Three of five laboratories using the quadruple test reported the screen positive, and two laboratories reported negative. In case of neural tube defect, all laboratories except one reported all specimens the screen negative. In case of Edward syndrome, all laboratories reported all specimens the screen negative.

CONCLUSIONS

Since MoMs and risk estimates showed a wide variation among the participating laboratories in this survey, an external quality control and the standardization of the variables seemed warranted.

Single large study or meta-analysis parameters: choosing the most appropriate tool for Down syndrome screening in the first trimester

AIM

The aim of the present study is to determine whether the use of population parameters derived from meta-analysis produces better test characteristics in the first-trimester combined screening than those obtained from large single studies, when screening for Down syndrome (DS) in singleton pregnancies.

METHODS

Retrospective analysis was done on a database of 4248 singleton pregnancies, including 13 cases of DS, for which the values of three markers used in the combined first-trimester test were available. The risk of DS was calculated for each mother from the different population parameters derived by meta-analysis or from two large single studies: the Fetal Medicine Foundation study (FMF) and the Serum, Urine and Ultrasound Screening Study (SURUSS).

RESULTS

When the detection rate was fixed at about 85%, the false-positive rate was significantly higher (Chi-square = 53.49, p < 0.0001) when the parameters obtained by the meta-analysis (6.25%) were compared with the two single studies (FMF, 4.15% and SURUSS, 3.75%).

CONCLUSIONS

This study highlights the importance of selecting appropriate population parameters when insufficient DS cases are available in the study population. When screening for DS in singleton pregnancies during the first trimester, the use of population parameters derived from single large studies produced better test characteristics.

First-trimester screening

Screening for fetal chromosome abnormalities, particularly for trisomy 21, has made dramatic advances. Better screening demonstrates that "high-risk" patients--particularly over age 35--can have lower risk of defects than younger unscreened women. This has caused reduction of amniocentesis for older patients and made screening available for younger patients who have the universal 2% to 3% risk. This means lower procedural-related losses of normal fetuses, and better resource allocation. The trend toward first-trimester detection of structural defects continues; a normal survey is reassuring and helps exclude major defects. Based on screening results, patients can be triaged into early follow-up and possible amniocentesis as 14 to 16 weeks, or a later detailed anatomic survey at 18 to 20 weeks.

The classification, functions and clinical use of different isoforms of HCG

HCG is composed of two subunits, HCGalpha and HCGbeta. During early pregnancy, HCG stimulates progesterone production in the corpus luteum, and injection of HCG is widely used to induce ovulation in assisted reproduction treatment (ART). Under experimental conditions, the free subunits have been shown to exert functions other than those of HCG, but the relevance of these remains to be determined. Intact HCG, free subunits and degraded forms of these occur in biological fluids, and determinations of these are important for diagnosis and monitoring of pregnancy, pregnancy-related disorders and several types of cancer. Development of optimal methods for the various forms has been hampered by lack of appropriate standards and expression of the concentrations of the various forms in units that are not comparable. Furthermore, the nomenclature for HCG assays is confusing and in some cases misleading. These problems can now be solved; a uniform nomenclature has been established, and new standards are available for HCG, its subunits HCGalpha and HCGbeta, the partially degraded or nicked forms of HCG and HCGbeta, and the beta-core fragment. This review describes the biochemical and biological background for the clinical use of determinations of various forms of HCG. The clinical use of HCG and studies on HCG vaccines are briefly reviewed.