Prenatal diagnosis of diverse chromosome abnormalities in a population of patients identified by triple-marker testing as screen positive for Down syndrome

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

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

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.

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.

Update and Review: Maternal Serum Screening

Maternal serum levels of alpha fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) can be used to screen pregnancies for neural tube defects, Down syndrome, Trisomy 18, and pregnancy complications. This article summarizes the most recent information regarding maternal serum screening, including genetic counseling issues.

Early amniocentesis as a method of choice in diagnosing gynecological diseases

INTRODUCTION

The aim of prenatal diagnosis is to detect fetal structural and genetic abnormalities. Used are different medical methods, procedures, processes and techniques. For this reason we can speak about the prevention and detection of hereditary diseases and congenital anomalies in the unborn fetus.

MATERIAL AND METHODS

The authors analyzed the results of early amniocentesis tests performed during 2009 in Institute for Gynecology, Infertility and Perinatology "Mehmedbasic" in Sarajevo. Performed is 299 analysis of amniotic fluid after amnion puncture done in the Institute or at the Clinic of Gynecology and Obstetrics (GAK) Sarajevo.

RESULTS AND DISCUSSION

INDICATIONS FOR THE PERFORMANCE OF EARLY AMNIOCENTESIS WERE: age greater over 35 (84.9%), positive ultrasound markers (1.6%), positive biochemical markers (5.6%) and positive family history for hereditary diseases (7.9%). Detected was 19 pathological cariograms or very high 7% of the total annual number of amniocentesis. An analysis of the distribution of pregnant women in relation to the indication of the result of cytogenetic analysis for each table made positive predictive value (PPV). For indicator age PPV was 0.11, 0.66 for ultrasound markers, for biochemical markers 0.13, for other indications-0.04. The logistic regression model (odds -ratio 11.234 ) indicate a positive ultrasound findings in relation to the year indicates that the risk to gain abnormal fetal karyotype 13 times higher when using only age as an indication for early amniocentesis. Of the 19 pathological cariogram largest number refers to M.Down (10), Sy. Edwards was detected in 2 patients, Sy. Klinefelter in 3, mosaicism in 3 and translocation gene in two of the fetus.

CONCLUSION

The authors would like to acknowledge a very high percentage of pathological cariogram risk groups, the extension of indications for RAC indicate the value of ultrasound markers as a good screening methods and the need for social incentives to perform screening tests and early amniocentesis in B&H in order to prevent genetic abnormalities.

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.

Misconstructions in health economics applied to the evaluation of prenatal screening

The application of economic evaluation to prenatal screening has led to ethical debates about the joint risks of rationing and eugenics. These debates have chosen the wrong target, as economic evaluations espouse the hypotheses and value judgment of their commissioners. This paper explores the difficulties in interpreting and using the results of economic evaluations. The first set of difficulties concerns the diversity in end points and the lack of an aggregate end point to reflect a generally desirable outcome. Another set results from the wider societal implications of economic evaluations and the implicit value judgments. Misunderstandings of the methods used for the economic evaluation of prenatal screening result from the lack of clearly stated objectives from policy makers.

Second-trimester prenatal screening for trisomy 21 using biochemical markers: a 7-year experience in one cytogenetic laboratory

BACKGROUND

Screening for trisomy 21 in the second trimester of pregnancy using biochemical markers is an established part of prenatal care in many developed countries.

OBJECTIVE

The present study was aimed at determining the incidence of trisomy 21 and other chromosomal abnormalities in women undergoing prenatal chromosome analysis after a second-trimester biochemical screening.

RESULTS

A total of 2832 karyotypes were analyzed following a positive second-trimester maternal serum screening (risk > or = 1/250) between 1998 and 2004. Thirty-nine cases of trisomy 21 and 40 other chromosomal abnormalities were detected. The positive predictive value was 1 in 73 karyotypes for trisomy 21 and 1 in 71 for the other chromosomal abnormalities. However, a temporal decline in the detection rate of trisomy 21 was noted, from 1/63 in 1998 to 1/221 in 2004. This change was attributable to an increasing number of pregnant women having first-trimester ultrasound nuchal translucency measurement.

CONCLUSION

Given the fact that nuchal translucency measurement combined with first-trimester biochemical marker screening has a positive predictive value of trisomy 21 comparable to that obtained following second-trimester biochemical screening, we should question whether to move trisomy 21 screening by maternal serum markers from the second trimester to the first trimester in conjunction with nuchal translucency measurement. Furthermore, genetic counseling prior to the amniocentesis should discuss the relatively high probability that a chromosomal abnormality other than trisomy 21 may be identified.

Prenatal diagnosis of 47,XXX

We report 2 cases of 47,XXX that were diagnosed prenatally and were screened positive for trisomy 21 by biochemical and ultrasound markers. These cases underline the importance of discussing the sex chromosome abnormalities during the genetic counseling after an abnormal triple screen test or ultrasound examination.

Prenatal diagnosis of de novo terminal deletion of chromosome 7q

OBJECTIVES

To present the prenatal diagnosis and perinatal findings of a de novo terminal deletion of chromosome 7q.

CASE

Amniocentesis was performed at 21-weeks gestation owing to a positive result of maternal serum multiple-marker screening. The 30-year-old woman, gravida 2, para 1, had a maternal serum multiple-marker screening test at 18-weeks gestation. The risk of Down syndrome was 1/11 calculated from the gestational age, maternal age, a maternal serum alpha-fetoprotein level of 1.026 multiples of the median (MOM), and a maternal serum free beta-human chorionic gonadotrophin (hCG) level of 8.678 MoM. Cytogenetic analysis of the cultured amniotic fluid cells revealed a de novo terminal deletion of 7q, 46,XX,del(7)(q35). Ultrasonography showed intrauterine growth restriction, microcephaly, and tetralogy of Fallot. The pregnancy was terminated subsequently. Grossly, the placenta was normal. On autopsy, the proband additionally manifested a prominent forehead, hypertelorism, epicanthus, upslanting palpebral fissures, a flat and broad nasal bridge, micrognathia, large low-set ears, overriding toes, and a normal brain. Radiography demonstrated a normal spine. Fluorescence in situ hybridization analysis demonstrated a 7q terminal deletion. Genetic marker analysis showed a maternally derived terminal deletion of chromosome 7(q35-qter).

CONCLUSION

Fetuses with a de novo 7q terminal deletion may be associated with a markedly elevated maternal serum hCG level and abnormal sonographic findings of intrauterine growth restriction, microcephaly, and congenital heart defects in the second trimester.

Advances in prenatal screening for Down syndrome: I. general principles and second trimester testing

BACKGROUND

Down syndrome is one of the most important causes of mental retardation in the population. In the absence of prenatal screening and diagnosis, prevalence at birth in the United States would currently exceed 1:600. The purpose of prenatal screening is to identify those women at the increased risk for an affected pregnancy and to maximize the options available to these women.

TESTS AVAILABLE

Second trimester serum screening involves combining the maternal age-specific risk for an affected pregnancy with the risks associated with the concentrations of maternal serum alpha-fetoprotein (MSAFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG) (triple testing). A forth analyte, inhibin-A (INH-A), is increasingly being utilized (quadruple testing). Optimal second trimester screening requires the integration of a number of clinical variables, the most important of which is an accurate assessment of gestational age. In addition to Down syndrome, the triple and quadruple tests preferentially identify fetal trisomy 18, Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith-Lemli-Opitz syndrome, and steroid sulfatase deficiency. Some programs modify the Down syndrome risks generated through maternal serum screening tests with fetal biometric data obtained by ultrasound. Other second trimester tests have shown promise, including the analysis of maternal urine and fetal cells in the maternal circulation, but none are in routine clinical use.

CONCLUSION

The second trimester triple and quadruple tests provide benchmarks for evaluating new screening protocols. The combination of fetal biometry, new test development as well as clarification of the role of co-factors that affect the concentrations of analytes in existing tests should lead to greater efficacy in second trimester screening for Down syndrome.

Second trimester maternal serum analytes in triploid pregnancies: correlation with phenotype and sex chromosome complement

Second trimester maternal serum alpha-fetoprotein (MS-AFP), human chorionic gonadotrophin (hCG), unconjugated estiol (uE3), and inhibin-A (INH-A) levels were evaluated in pregnancies complicated by triploidy. In addition to seven new triploid pregnancies, the results for 67 published cases were reviewed. All cases appear to fall into two major groups. First, those identifiable as screen-positive for both Down syndrome and an open neural tube defect (ONTD) with elevated MS-AFP, grossly elevated hCG, low/normal uE3, and probably elevated INH-A. Pregnancies in the second group are identifiable as screen-positive for trisomy 18 with low/normal MS-AFP, and very low hCG, uE3 and INH-A. Triploid pregnancies with high maternal serum hCG nearly always show a placenta with partial mole (25/27 or 93%), a high frequency of ONTDs or ventral wall defects (VWDs) (8/28 or 29%) and have either an XXX or XXY karyotype (observed ratio 6:10, respectively). Low hCG is infrequently associated with a molar placenta (1/11 or 9%), does not appear to be associated with ONTDs or VWDs (0/29 or 0%), and shows an excess of XXX over XXY karyotypes (observed ratio 17:2). There were 16 cases with either a molar placenta, an ONTD or a VWD that received the MS-AFP and hCG tests. All 16 were screen-positive for an ONTD (MS-AFP> or =2 multiples of the median). In addition, all 31 cases that received MS-AFP, hCG, uE3 (and where available INH-A) were screen-positive for either Down syndrome or trisomy 18. The findings are discussed in the context of expected differences between digynic and diandric triploidy. It is suggested that the sex chromosome complement in triploidy is an important factor in determining risk for partial mole development and in utero survival.

Karyotypes found in the population declared at increased risk of Down syndrome following maternal serum screening

Of the 65 328 pregnancies of South Australian mothers screened by the South Australian Maternal Serum Antenatal Screening (SAMSAS) Programme between 1 January 1991 and 31 December 1997, 3431 (5.25%) were declared at increased risk of fetal Down syndrome. Fetal or neonatal karyotype was determined in 2737/3431 (79.8%) of these pregnancies, including 16 with early fetal loss. Interrogation of the database of the South Australian Neonatal Screening Service showed 643 live-born infants whose phenotype was not subsequently questioned among the 694 pregnancies whose karyotype was not determined. Of the remaining 51/3431 pregnancies, 19 ended in early fetal loss without karyotyping and no newborn screening or other records could be found for 32 cases. The 129 instances of abnormal karyotype found were Down syndrome (84), trisomy 18 (four), trisomy 13 (three), triploidy (two), female sex chromosome aneuploidy (six) and male sex chromosome aneuploidy (five), inherited balanced rearrangements (19), mosaic or de novo balanced abnormalities (four) and unbalanced karyotypes (two). In the pregnancies declared at increased risk of fetal Down syndrome, only the karyotype for Down syndrome occurred with a frequency greater than that expected for the general, pregnant population.

Elevated maternal serum alpha-fetoprotein with low unconjugated estriol and the risk for lethal perinatal outcome

OBJECTIVE

To determine whether a combination of elevated maternal serum alpha-fetoprotein (MSAFP) and low unconjugated estriol (E3) concentration identifies pregnancies at particularly high risk for fetal abnormality or poor outcome.

METHODS

Pregnancy outcomes were reviewed for women with elevated MSAFP (> or =2.0 MoM) from our database of 50,315 women who had received triple marker testing from 1993-1998. Outcomes for those with low E3 (< or =0.7 MoM) were compared with those with normal E3 (>0.7 MoM). The incidences of fetal death, neural tube defects, chromosome abnormalities, congenital abnormalities, preterm birth, small-for-gestational age (SGA), twins, and inaccurate dates were compared in the two groups using Fisher's exact test with P < 0.05 considered significant.

RESULTS

Of the 50,315 women screened, 1,435 (2.85%) had an elevated MSAFP. Pregnancy outcomes were obtained in 94% of those with elevated MSAFP and 70% of all patients screened. Neural tube defects were present in 57 fetuses/infants (21 anencephalic, 29 spina bifida, 7 encephalocele) of which 46 (81%) had an elevated MSAFP. Of the 1,435 women with an elevated MSAFP, 199 (14%) had a low E3. Compared to those women with elevated MSAFP but normal E3, women with elevated MSAFP and low E3 were at significantly increased risk for fetal death (20.6% vs. 2.8%, relative risk (RR) 8.9), anencephaly (9.0% vs. 0.1%, RR 122.8) and chromosome abnormality (2.5% vs. 0.6%, RR 4.0).

CONCLUSIONS

Pregnancies complicated by elevated second trimester MSAFP and low E3 are at a particularly high risk (32%) for lethal perinatal outcomes. Twins, while a common cause of elevated MSAFP, are rarely found when an elevated MSAFP is associated with low E3.

Unexplained elevated midtrimester maternal serum levels of alpha fetoprotein, human chorionic gonadotropin, or low unconjugated estriol: recurrence risk and association with adverse perinatal outcome

OBJECTIVE

To determine if women experiencing an unexplained elevated maternal serum alpha fetoprotein (MSAFP; > or =2.0 MoM) or human chorionic gonadotropin (hCG; > or =2.0 MoM), or low unconjugated estriol (E3; < or =0.5 MoM) in one pregnancy are at increased risk for similar results in a subsequent pregnancy, and to determine if recurrence of these analyte extremes is associated with adverse perinatal outcome.

METHODS

We identified all women delivering two consecutive singleton pregnancies at one hospital between 1992-1997 for whom second trimester trisomy 21 serum screen was performed in each pregnancy. All screens were performed in a single laboratory. Each pregnancy delivered after 20 weeks and had gestational age confirmed by ultrasound prior to 24 weeks. Subjects were excluded if a fetal anomaly or aneuploidy was present. Adverse outcomes included abruption, oligohydramnios, preeclampsia, preterm membrane rupture, preterm delivery, stillbirth, birthweight <10th centile, and admission to neonatal intensive care unit (NICU).

RESULTS

A total of 538 women had 1,076 pregnancies meeting inclusion criteria; 12/515 (2.3%) of women with a normal MSAFP, 28/470 (6.0%) with a normal hCG, and 11/504 (2.2%) with a normal E3 in the first pregnancy had an anomalous result for the respective analyte in the second pregnancy. In contrast, only 4/23 (17.4%) patients with an elevated MSAFP (P = 0.003), 14/44 (31.8%) with an elevated hCG (P < 0.001), and 2/10 (20.0%) with a low E3 (P < 0.025) in the first pregnancy had the same analyte anomaly recur in the second pregnancy. The odds ratios for recurrent elevated MSAFP, hCG, and low E3 were 7.5, 5.3, and 9.2, respectively. Adverse perinatal outcomes occurred with similar frequency, regardless of MSAFP, hCG, or E3 results in consecutive pregnancies, using women with normal MSAFP, hCG, and E3 results in one or both pregnancies as controls.

CONCLUSIONS

Women experiencing an anomalous serum analyte in one pregnancy are at significant risk to experience the same analyte result in a subsequent pregnancy.

Prenatal diagnosis of trisomy 20 mosaicism by maternal serum screening for Down syndrome

We report two cases of prenatally diagnosed trisomy 20 mosaicism associated with positive Down syndrome screening at 16 weeks' gestation. Both infants exhibited normal growth and mental development. These cases suggest that the multiple-marker screening test may play an important role in prenatal detection and diagnosis of chromosomal anomalies in addition to Down syndrome.

Predictive value of the triple screening test for the phenotype of Down syndrome

Maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) are routinely measured in the second trimester ("triple" test) and combined with maternal age to evaluate risk for fetal Down syndrome. Triple test results and clinical findings were retrospectively reviewed for 30 newborns with Down syndrome to determine whether analyte values or second trimester risks for Down syndrome were more extreme in affected pregnancies where cardiac or other severe congenital malformations were present compared to those cases where major anatomical abnormalities were absent. Mean MS-AFP, uE3, maternal age, and second trimester Down syndrome risk were all similar in the two groups of pregnancies. However, hCG concentrations did appear to be higher in the group of Down syndrome pregnancies with anatomical anomalies (mean 1.74 MoM versus 1.19 MoM) (P<0.05). Overall, there was no significant difference in the incidence of major anomalies in patients with screen-positive test results versus those cases that were not identified by the triple test. Prenatal counseling should therefore reflect the general expectations of the Down syndrome phenotype that have been established from live-born infants with this disorder.

Economic evaluation of prenatal screening for Down syndrome in the U.S.A

Maternal serum screening for Down syndrome involves biochemical tests such as alpha-fetoprotein (alpha FP), human chorionic gonadotrophin (hCG) and unconjugated oestriol (uE3), either alone or in combination, that have variable detection and false-positive rates. Choosing a screening protocol requires a trade-off between a desired detection rate and an acceptable false-positive rate. Selecting a screening protocol that maximizes the net benefit to society provides one approach. We have developed a general formula for calculating the per case net social benefit of a screening test and have applied it to United States data. The maximum net benefit associated with each of the various screening options currently available is estimated and the model is further applied to determine the conditions under which the addition of a new marker to an existing protocol can be justified. For each test, or combination of tests, optimal net benefits occur at different detection and false-positive rates. Net benefits are strongly and positively dependent on maternal age; high net benefits are associated with older patients and low, or even negative, net benefits with younger patients. Also, net benefits are affected by the term risk cut-off rate. For triple testing, the 1:351 Down syndrome term risk cut-off appears to provide a higher net benefit than that obtained with 1:250 or 1:300. The optimization of societal net benefit provides a powerful approach to evaluating screening strategies, but the policies used must also consider individuals' freedom in decision making at each step of the prenatal diagnosis pathway.

Triple-marker test as screening for Down syndrome: a meta-analysis

The effectiveness of triple-marker testing as screening for Down syndrome needs to be evaluated by means of formal meta-analytic techniques. We did a MEDLINE search to identify studies evaluating the detection of Down syndrome by use of the triple-marker test. Reference lists of articles were also checked. Papers published in either English, French, or German from 1966 to November 1996 were eligible for this review. Twenty cohort studies were identified. Results of sensitivities and false-positive rates from different subgroups of the study sample were compared by using summary receiver-operating characteristic curve analysis. Medians of sensitivities and false-positive rates were also estimated. A total of 194,326 patients were included. In women of all ages, the medians for sensitivities were 67, 71, and 73 percent when the cutoffs used were 1:190-200, 1:250-295, and 1:350-380, respectively. The median false-positive rates fluctuated between 4 and 8 percent. For women at or above 35 years old, the medians of sensitivity and false-positive rate were 89 and 25 percent, respectively, when the chosen cutoff was 1:190-200. In patients below 35 years old, the median sensitivity was 57 percent if the cutoff used was 1:250-295. Summary receiver-operating characteristic curves showed that 1:190 was the best cutoff for predicting Down syndrome. The triple-marker testing is an effective screening method of detecting Down syndrome pregnancies. It is less effective in younger than in older age groups and may be offered as an alternative to amniocentesis to pregnant women over 35.

Atypicality revisited: further data on the effectiveness of the Mahalanobis distance in Down's syndrome screening

Further data suggesting that assessment of atypicality may be a valuable addition to Down's syndrome screening is presented, based on results from 1521 unaffected pregnancies and 190 chromosomally abnormal pregnancies. For a 1% increase in false positive rates (over the Down's screening-related false positives), it is estimated that the detection of non-trisomy 21 abnormalities may be enhanced by approximately 40%. These false positive and detection rates are similar to previous reports for specific trisomy 18 screens. Further work is necessary to prove whether a specific trisomy 18 screen, or an atypicality screen is preferable.

Down syndrome and neural tube defect screening: the value of using gestational age by ultrasonography

OBJECTIVE

Our goal was to determine whether gestational age should be based on ultrasonographic evaluation or last menstrual period data in the interpretation of second-trimester maternal serum screening for Down syndrome and open neural tube defects.

STUDY DESIGN

Initial and revised screen-positive rates and detection rates were reviewed for women undergoing triple-marker testing (maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol). The study population consisted of > 24,000 women at 15.0 to 21.9 weeks' gestation with approximately 60% of test interpretations based on ultrasonographic evaluation of gestational age. Gestational age and screening results were compared for 24 Down syndrome pregnancies in which both ultrasonography and last menstrual period dating were available.

RESULTS

Both initial and revised screen-positive rates for Down syndrome were significantly lower when ultrasonographic data were used compared with last menstrual period dating. The detection rate for Down syndrome appeared to be higher with ultrasonographic dating (approximately 76% vs 60% for last menstrual period dating). Down syndrome fetuses had a significantly shorter gestational age when evaluated by ultrasonography (relative to last menstrual period dating), but a similar trend was also seen in control pregnancies. Initial and revised screen-positive rates for open neural tube defects were higher for women who had received an ultrasonographic examination compared with the rates for those women referred with only last menstrual period data. The detection rates for open neural tube defects were similar for both methods of pregnancy dating.

CONCLUSION

By use of ultrasonographic measurement of gestational age, the number of amniocenteses performed to detect Down syndrome can be substantially reduced while detection rates are maintained or improved.

Medians for second-trimester maternal serum α-fetoprotein, human chorionic gonadotropin, and unconjugated estriol; differences between races or ethnic groups

Second-trimester maternal serum α-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) are routinely measured in screening fetuses at high risk for Down syndrome or open neural tube defects (ONTD). For test interpretation, individual patient values of these three analytes are related to population-derived median values. We evaluated data from &gt;21 000 pregnancies to determine the extent of race-specific differences in median concentrations. For samples at most gestational ages, median AFP, hCG, and uE3 values for white, black, Hispanic, and other patients were all significantly different. Differences remained significant even when data were corrected for patient weights. For each analyte, the extent of the variation was not the same at different gestational ages. Differences in median values across race/ethnicity groups appear to have only a small impact in Down syndrome screening but it may be appropriate to use alternative sets of AFP medians or adjustment factors to AFP medians for some Asian populations receiving ONTD screening.