Maternal serum dimeric inhibin A in second-trimester Down's syndrome pregnancies

A technical and clinical evaluation of the new ThermoFisher BRAHMS unconjugated estriol and inhibin-A assays and their use in second trimester Down syndrome screening

To evaluate second-trimester Down syndrome screening performance of the new ThermoFisher BRAHMS GOLD unconjugated estriol (uE3) and inhibin-A assays. Serum samples were analyzed for levels of uE3 and inhibin-A using the ThermoFisher BRAHMS GOLD immunoanalyzer and compared to other platforms. Levels were transformed to multiples of the median (MoM) in unaffected pregnancies. Log₁₀ MoM distributions in unaffected and Down syndrome pregnancies were assessed for central tendency (mean) and dispersion (SD). Empirical and estimated screening performances were determined. Correlation between BRAHMS and AutoDELFIA^® uE3 and inhibin-A were 0.63 and 0.97, respectively, the respective mean difference was 31.3% [95%CI 50.2% to -112.8%] and -23.3% [95%CI -41.9% to -4.7%]. Passing-Bablok indicated significant systematic (-2.78 [95%CI -3.57 to -2.04]) and proportional bias (1.30 [95%CI 1.15 to -1.47]) between uE3 assays and significant proportional bias (0.71[95%CI 0.65-0.78]) between inhibin-A assays. The uE3 and inhibin-A log₁₀ MoM distribution mean [SD] in unaffected and Down syndrome pregnancies were 0.0024 [SD = 0.2341] and -0.0001 [SD = 0.2078], and -0.2028 [SD = 0.2495] and 0.3645 [SD = 0.2576], respectively. The new BRAHMS uE3 and inhibin-A assays had an 81-83% detection rate for Trisomy21 for a 5% false-positive rate. The new BRAHMS assays achieved the expected screening performance provided the risk estimation model is adjusted to account for the higher BRAHMS uE3 MoM measurement distribution variance.

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.

Screening for Down Syndrome in the United States: Results of Surveys in 2011 and 2012

Context.—Participants in a College of American Pathologists external proficiency testing program for first and second trimester Down syndrome screening.

Objectives.—To determine the number of women screened for Down syndrome in the United States, along with the type of test received and to compare those results to earlier surveys in 1988 and 1992.

Design.—Questionnaires regarding the type and number of Down syndrome tests performed per month were completed by participants in early 2011 and again in early 2012.

Results.—After accounting for some of the missing responses, data from up to 131 laboratories indicated that 67% (2 764 020 of 4 130 000) to 72% (2012: 2 963 592 of 4 130 000) of US pregnancies received prenatal screening for Down syndrome. Second trimester tests were most common (2012: 60%; 1 770 024 of 2 963 592), followed by integrated (2012: 21%; 627 876 of 2 963 592), and first trimester (2012: 19%; 565 692 of 2 963 592). The 6 largest laboratories tested 61% of screened pregnancies and offered the widest array of tests, while the smallest 32 tested 1% and almost always offered only second trimester tests.

Conclusions.—The current population estimate of 72% pregnancies screened annually is higher than estimates from 1988 (25%) and 1992 (50%). Available testing choices are also more varied, and all testing methods perform better than those methods available 10 years ago. Clinicians should ensure that women are offered tests that follow recommended best-practice testing protocols, and screening laboratories should assess whether patient needs are being met.

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.

Biochemical screening for congenital defects

This article discusses biochemical screening for congenital defects. Biochemical screening remains the standard for estimating the risk of aneuploidy in pregnancy. The combination of first and second trimester markers promises to further improve diagnostic accuracy for anomaly detection.

Inhibins and activins in human fetal abnormalities

To date, the only routine clinical application of inhibin or activin measurement in testing for fetal abnormalities has been the use of inhibin A in prenatal screening for trisomy 21 (Down syndrome). Second trimester maternal serum levels of inhibin A are, on average, two-fold higher in Down syndrome than in unaffected pregnancies. Although the biology of altered second trimester maternal serum analyte levels in Down syndrome pregnancy cannot yet be explained, it seems that fetal products tend to be decreased, while placental products tend to be increased. This pattern holds true for inhibin A because maternal serum levels appear to be derived from placental rather than fetal sources. Therefore, the measurement of inhibins and activins in maternal fluids, although clinically useful and relatively easy to obtain, may not be helpful in studying their role in human fetal development. Studies in transgenic mice indicate a role for activin, follistatin, and activin receptor type IIA in development of the palate and craniofacial region. Cleft palate is a common birth defect and is associated with serious feeding and respiratory complications in newborns. We have begun to investigate the potential role of activin in human craniofacial development by examining the spatial and temporal expression of inhibin/activin subunits, follistatin and the activin receptors in the fetal palate. Palate tissues were collected at autopsy from fetuses ranging in gestational age from 9 to 42 weeks, and 8 week embryonic tissues were also examined. Tissues were either stored in paraffin for immunocytochemistry or were frozen for RT-PCR examination of the expression of inhibin/activin proteins or mRNAs, respectively. To date, betaA subunit, follistatin, and activin receptor, but not alpha and betaB subunit, mRNAs are present in palate tissues and inhibin/activin betaA immunoreactivity has been consistently observed in developing bone. Expression of the activin A subunit and its receptors in the human fetal palate are consistent with a developmental role. Studies are ongoing to determine whether altered activin biosynthesis is associated with cleft palate. Future studies of fetal tissues may help to elucidate other roles for the TGF-beta family in human development.

Molecular weight forms of inhibin A, inhibin B and pro-alphaC in maternal serum, amniotic fluid and placental extracts of normal and Down syndrome pregnancies

BACKGROUND

Inhibin A, an established prenatal marker of Down syndrome (DS), exists in the maternal circulation in a number of isoforms. The present study explored whether specific inhibin A isoforms may be selectively increased in DS, offering the prospect of improved marker performance.

METHODS

Second trimester maternal serum, placental extracts and amniotic fluid (AF) pools from both normal and DS pregnancies were fractionated by a combined immunoaffinity (IA) chromatography, preparative polyacrylamide gel electrophoresis (Prep-PAGE) and electroelution procedure. Inhibins A, B and pro-alphaC were determined in the eluted fractions by specific enzyme-linked immunosorbent assays (ELISAs) and the profiles of immunoactivity (IA) characterized in terms of molecular weight (MW) and percentage recovery.

RESULTS

The MW patterns of inhibin A and pro-alphaC in maternal serum and AF were similar between DS and control pregnancies, both showing peaks between 25-40 k and approximately 65 k. AF contained, in addition, a higher proportion of <30 k inhibins A and B, and <25 k pro-alphaC forms. There were large differences in the inhibin forms present in DS placentae, with more 70 k and less 30-40 k inhibin A than in controls.

CONCLUSIONS

The present data suggest that the processing, cleavage or secretion of inhibin MW forms by the DS placenta differs from normal. However, these differences are not reflected in maternal serum and so improvements in serum screening will not be afforded by measuring specific inhibin A isoforms.

Activins, inhibins, and follistatins: from endocrinology to signaling. A paradigm for the new millennium

It has been 70 years since the name inhibin was used to describe a gonadal factor that negatively regulated pituitary hormone secretion. The majority of this period was required to achieve purification and definitive characterization of inhibin, an event closely followed by identification and characterization of activin and follistatin (FS). In contrast, the last 15-20 years saw a virtual explosion of information regarding the biochemistry, physiology, and biosynthesis of these proteins, as well as identification of activin receptors, and a unique mechanism for FS action-the nearly irreversible binding and neutralization of activin. Many of these discoveries have been previously summarized; therefore, this review will cover the period from the mid 1990s to present, with particular emphasis on emerging themes and recent advances. As the field has matured, recent efforts have focused more on human studies, so the endocrinology of inhibin, activin, and FS in the human is summarized first. Another area receiving significant recent attention is local actions of activin and its regulation by both FS and inhibin. Because activin and FS are produced in many tissues, we chose to focus on a few particular examples with the most extensive experimental support, the pituitary and the developing follicle, although nonreproductive actions of activin and FS are also discussed. At the cellular level, it now seems that activin acts largely as an autocrine and/or paracrine growth factor, similar to other members of the transforming growh factor beta superfamily. As we discuss in the next section, its actions are regulated extracellularly by both inhibin and FS. In the final section, intracellular mediators and modulators of activin signaling are reviewed in detail. Many of these are shared with other transforming growh factor beta superfamily members as well as unrelated molecules, and in a number of cases, their physiological relevance to activin signal propagation remains to be elucidated. Nevertheless, taken together, recent findings suggest that it may be more appropriate to consider a new paradigm for inhibin, activin, and FS in which activin signaling is regulated extracellularly by both inhibin and FS whereas a number of intracellular proteins act to modulate cellular responses to these activin signals. It is therefore the balance between activin and all of its modulators, rather than the actions of any one component, that determines the final biological outcome. As technology and model systems become more sophisticated in the next few years, it should become possible to test this concept directly to more clearly define the role of activin, inhibin, and FS in reproductive physiology.

Measurement of inhibin A: a modification to an enzyme-linked immunosorbent assay

Inhibin A is a useful prenatal marker of Down syndrome. Currently, the available enzyme-linked immunosorbent assays (ELISAs) for inhibin A are based upon the same paired monoclonal antibodies. In the present study we have confirmed for one of those ELISAs that short-term sample storage as whole blood leads to a significant decline in detectable inhibin A and that this is most likely due to erythrocyte catalase interference with a critical oxidation step in the assay. While this interference can be eliminated by heating the samples pre-assay, this process is labour intensive. In the present study we have demonstrated that the addition of 3-amino-1,2,4-triazole (AT), a catalase 'suicide' inhibitor, also prevents the decline of inhibin A levels in samples stored as whole blood. We suggest that the addition of AT to samples prior to assay is a simple modification to the inhibin A ELISA that affords optimum performance.

Placental and maternal serum inhibin-A and activin-A levels in Down's syndrome pregnancies

The objective of this study was to analyse the levels of inhibin-A and activin-A in maternal serum and placental tissue from Down's syndrome (DS) pregnancies. Inhibin-A and activin-A levels were determined by specific immunoassays and individual results were expressed as multiples of the control median (MoM) at the appropriate gestation. Immunohistochemistry was used to localize inhibin alpha and beta(A)-subunits in a selection of placental sections. In DS pregnancies, median inhibin-A levels were found to be significantly elevated to 1.46 MoM (P< 0.05) in placental extracts, and 2.06 MoM (P< 0.0001) in maternal serum, when compared with uncomplicated pregnancies. Median activin-A MoMs were also elevated in placental extracts and maternal serum to 1.62 MoM (P< 0.01), and 1.26 MoM (P< 0.05), respectively. Immunohistochemistry revealed that the alpha subunit of inhibin-A and the beta(A)subunit of inhibin-A and activin-A were mainly localized to the trophoblastic layer of placental villi. Semiquantitative studies of staining intensity revealed a trend towards stronger staining of placental trophoblasts and stroma of DS tissues, although this was statistically significant only for beta(A)subunit staining of trophoblasts (P< 0.05). These results support the hypothesis that maternal serum levels of inhibin-A and activin-A are elevated due to increased production in the placenta, and increased immunostaining of trophoblasts suggests that this may be due to increased production in the trophoblasts.

Comparison of urinary hyperglycosylated human chorionic gonadotropin concentration with the serum triple screen for Down syndrome detection in high-risk pregnancies

OBJECTIVE

Both modest screening performance and declining patient and physician acceptance have stimulated interest in alternative markers to the triple screen for the detection of Down syndrome. Our purpose was to compare the concentration of a single urinary analyte, hyperglycosylated human chorionic gonadotropin, with the serum triple screen (alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol concentrations combined with age) for second-trimester Down syndrome detection.

STUDY DESIGN

Urine and blood were obtained from pregnant women in the second trimester undergoing genetic amniocentesis. Urinary hyperglycosylated human chorionic gonadotropin concentration and serum triple-screen values were measured. Individuals undergoing amniocentesis because of abnormal triple-screen results were excluded. Individual Down syndrome risks on the basis of urinary hyperglycosylated human chorionic gonadotropin concentration plus maternal age and on the basis of the triple-screen results were calculated. For each algorithm the sensitivity and false-positive rate for Down syndrome detection at different risk thresholds were determined. From these values receiver operating characteristic curves were constructed, and the area under the curve was determined for each algorithm. Finally, the performance of a new combination in which urinary hyperglycosylated human chorionic gonadotropin concentration replaced serum human chorionic gonadotropin concentration in the triple screen was ascertained.

RESULTS

We studied 24 pregnancies complicated by Down syndrome and 500 unaffected pregnancies between 14 and 22 weeks' gestation in a mostly white (93.5%) population undergoing amniocentesis primarily because of advanced maternal age. The sensitivity and false-positive rate for urinary hyperglycosylated human chorionic gonadotropin concentration were 75. 0% and 5.6%, respectively, whereas those for the triple screen were 75.0% and 33.2%, respectively. Urinary hyperglycosylated human chorionic gonadotropin concentration was superior to the triple screen (area under the curve, 0.9337 vs 0.7887; P =.02). The substitution of urinary hyperglycosylated human chorionic gonadotropin concentration for serum human chorionic gonadotropin concentration in the triple screen resulted in a 91.7% sensitivity at a 10.0% false-positive rate, versus a 54.2% sensitivity for the traditional triple screen at the same false-positive rate.

CONCLUSION

The performance of urinary hyperglycosylated human chorionic gonadotropin concentration was statistically superior to that of the serum triple screen in a high-risk population. The use of urinary hyperglycosylated human chorionic gonadotropin concentration as an alternative test or substitution of this measurement for serum human chorionic gonadotropin concentration in the triple screen would improve diagnostic accuracy and address many current concerns related to the triple screen.

Second-trimester maternal serum inhibin-A screening for fetal Down syndrome in Asian women

Case control studies in the Caucasian population showed that maternal serum inhibin-A is elevated in Down syndrome pregnancies and may be a useful second-trimester marker in addition to human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP). Data in the Asian population are lacking. We measured inhibin-A levels in the stored maternal sera of 49 Down syndrome pregnancies and 341 controls with a commercially available assay and expressed them as the multiples of the median of the gestational week. The log means and standard deviations for case and control inhibin-A MOMs were 0.209, 0.226, and 0.002 and 0.177, respectively. Median inhibin-A MOM in Down syndrome cases was elevated to 1.62 (95 per cent confidence interval, 1.29-1.82). 36 per cent of Down syndrome cases were expected to be detected at a 5 per cent false-positive rate. However, inhibin-A MOMs were strongly correlated with hCG MOMs in the cases (r=0.73, p<0.001) and the controls (r=0.56, p<0.001). This will diminish the value of adding inhibin-A to the existing hCG and AFP screening protocol.

Inhibin A and pro-alpha C inhibin in Down syndrome and normal pregnancies

Using two enzyme-linked immunosorbent assays specific for inhibin A and pro-alpha C inhibin, levels of the two proteins were assessed in maternal serum from 43 Down syndrome and 300 chromosomally normal pregnancies at 15-17 weeks' gestation. Compared to the control pregnancies, both inhibin A and pro-alpha C inhibin were significantly elevated in the Down syndrome pregnancies with median levels, expressed as multiples of the normal median, of 1.53 MoM and 1.34 MoM, respectively (P < 0.001 and P = 0.046 compared to controls). Levels of inhibin A and pro-alpha C inhibin were weakly but significantly correlated in both the control and the Down syndrome sera (r = 0.25, P < 0.0001; r = 0.4, P = 0.008, respectively). These data suggest that the mechanism(s) underlying the elevated inhibin levels observed in Down syndrome may affect the regulation of both the inhibin alpha- and beta A-subunits.

Evolution of an inhibin A ELISA method: implications for Down's syndrome screening

The development of a sensitive and specific enzyme-linked immunoassay (ELISA) for inhibin A stimulated the observation that inhibin A was a useful prenatal marker of Down's syndrome. Modifications of that ELISA, in terms of preassay sample treatment, detection methods and standard preparation, were subsequently introduced to improve assay performance and reduce costs. These modified formats have been validated and reported. We describe the modifications in detail, explaining the rationale for each, and report the results of a study directly comparing the various ELISA formats in terms of assay performance when applied to clinical samples and ability to differentiate between normal and Down's syndrome pregnancies. A format involving sample pretreatment with sodium dodecylsulphate at 100 degrees C was found to give better assay performance and a modest improvement in discrimination between Down's syndrome samples and controls, and we recommend this format for use by other investigators.

Elevated second-trimester dimeric inhibin A levels identify Down syndrome pregnancies

OBJECTIVE

Our purpose was to determine whether second-trimester dimeric inhibin A levels distinguish Down syndrome pregnancies from euploid pregnancies.

STUDY DESIGN

With use of a commercially available enzyme-linked immunosorbent assay (Serotec, Oxford) inhibin A medians were established in stored sera from 40 to 50 euploid pregnancies at each week of gestation from 14 to 20 weeks and from 33 Down syndrome pregnancies. Maternal serum alpha-fetoprotein, unconjugated estriol, and human chorionic gonadotropin levels measured in each sample before storage were retrieved. The performance of inhibin A in the multiple-marker screening test was evaluated.

RESULTS

The mean inhibin A multiple of the median was significantly higher in the Down syndrome group than in the euploid group (2.84 +/- 2.0 vs 1.22 +/- 1.0, p = 0.0001). An inhibin A level > or = 1.6 multiples of the median identified 70% of all Down syndrome pregnancies at a false-positive rate of 22%. Replacing estriol with inhibin A in the multiple-marker screening test resulted in a higher Down syndrome detection rate at a lower screen-positive rate.

CONCLUSION

Elevated second-trimester maternal serum inhibin A levels identify Down syndrome pregnancies; replacing estriol with inhibin A in the multiple-marker screening test improves test performance.

Maternal serum inhibin-A and free beta-hCG concentrations in trisomy 21 pregnancies at 10 to 14 weeks of gestation

OBJECTIVE

To determine the relation between maternal serum inhibin-A and free beta-hCG concentrations in chromosomally normal pregnancies and to compare the two biochemical markers for their sensitivity in identifying trisomy 21 pregnancies.

SAMPLE

Inhibin-A and free beta-hCG were measured in maternal serum samples from 800 chromosomally normal singleton pregnancies at 10 to 14 weeks of gestation and 76 singleton pregnancies with fetal trisomy 21.

RESULTS

In the normal group maternal serum inhibin-A was significantly associated with both maternal weight and gestational age (F = 11.2, P < 0.0001). In pregnancies with trisomy 21 the maternal serum inhibin-A and free beta-hCG concentrations were significantly increased (mean difference inhibin = 0.51 SD, F = 18, P < 0.0001 and mean difference free beta-hCG = 1.13 SD, F = 80, P < 0.0001). For a 5% false positive rate, the sensitivity of maternal serum free beta-hCG in identifying pregnancies with trisomy 21 was 28.9% compared with 12.8% for maternal serum inhibin-A. Delta inhibin-A was significantly associated with delta-free beta-hCG (r = 0.345, P < 0.01) and the deviation from the normal mean for free beta-hCG was significantly greater than the deviation for inhibin-A (t = 4.0, P < 0.0001). For a 5% false positive rate, the sensitivity achieved by combining information from delta inhibin-A and delta free beta-hCG was similar to the sensitivity of free beta-hCG alone (30.3% compared with 28.9%).

CONCLUSION

At 10 to 14 weeks of gestation fetal trisomy 21 is associated with increased maternal serum inhibin-A and free beta-hCG levels. However, the degree of elevation of inhibin-A is less than that of free beta-hCG, and there is a significant association between levels of the two proteins. The sensitivity for trisomy 21 achieved with the combination of maternal serum inhibin-A and free beta-hCG is not significantly different from that achieved with maternal serum free beta-hCG alone.

Maternal serum screening for fetal genetic disorders

Maternal serum analyte screening is an integral component of contemporary antenatal care. Based on elevated MSAFP levels, 85% to 90% of NTDs (e.g., anencephaly or spina bifida) can be detected. Using a combination of serum analytes (e.g., MSAFP, hCG, UE3) 55% to 60% of fetal Down's syndrome can be detected. Future strategies for Down's syndrome screening may include the use of new markers such as dimeric inhibin-A and urinary beta-core fragment of hCG, as well as first-trimester screening, particularly with PAPP-A and free beta-hCG.

Combining inhibin A with existing second-trimester markers in maternal serum screening for Down's syndrome

To assess the value of inhibin A as an additional second-trimester maternal serum marker of Down's syndrome we studied 56 affected and 280 unaffected pregnancies matched for gestational age. The median level in the cases was 1.62 multiples of the gestation-specific median (MOM) in the controls, with 95 per cent confidence limits of 1.34-1.96. The distribution of inhibin levels in affected and unaffected pregnancies was approximately log Gaussian, with means about 1 standard deviation apart. This degree of separation was similar to that for human chorionic gonadotropin (hCG), free beta-hCG, and unconjugated oestriol (uE3), but about double that of alpha-fetoprotein (AFP) measured in the same samples. Inhibin was largely uncorrelated with AFP and uE3, whereas the log correlation coefficient with hCG was 0.29 (P = 0.19) for Down's syndrome and 0.41 (P < 0.0001) for unaffected pregnancies; with free beta-hCG, it was 0.18 (P = 0.38) and 0.38 (P < 0.0001), respectively. On the basis of these results and other published studies, we estimate that measuring inhibin A in addition to AFP and hCG or free beta-hCG (with or without uE3) will increase the detection rate for a fixed 5 per cent false-positive rate by about 7 per cent.

Second-trimester dimeric inhibin-A in Down's syndrome screening

Initial studies of immunoreactive inhibin using a commercial assay have shown levels to be increased in three second-trimester series of maternal samples from Down's syndrome-affected pregnancies. This assay detected non-specifically all forms of circulating inhibin, dimeric and free alpha subunits, whether fully or partially processed. More recently, a new specific assay for dimeric inhibin-A has shown elevated results in both a first-trimester and a second-trimester series of cases. In order to assess the value of dimeric inhibin-A as a potential marker in the second trimester, we have analysed 157 Down's syndrome cases and used 367 unaffected cases across the gestational range 14-20 weeks to establish control medians and population parameters. In our series, the median MOM in Down's cases was 1.77, significantly higher than in the controls. At a 5 per cent false-positive rate, dimeric inhibin-A alone identified 37 per cent of cases. When used in conjunction with maternal age and other marker combinations, mathematical modelling showed detection rates rising from 48 per cent (inhibin-A plus age) to 61 per cent (inhibin-A, free beta hCG, age) and 68 per cent (inhibin-A, AFP, free beta hCG, age). Our data suggest that dimeric inhibin-A may have greater potential earlier in gestation when median levels at 14-16 weeks are 1.92 compared with 1.46 at 17-23 weeks. Dimeric inhibin-A may be a valuable addition to screening protocols, particularly in early gestations.

Maternal serum inhibin-A levels in twin pregnancies: implications for screening for Down's syndrome

A nested case-control study using stored serum samples collected as part of a prospective study of the outcome of pregnancy was performed to investigate concentrations of (dimeric) inhibin-A in maternal serum between 15 and 22 weeks of pregnancy in 200 twin pregnancies and 600 singleton control pregnancies. Each twin pregnancy was matched with three singleton pregnancies for gestational age (same completed week) and duration of sample storage (same calendar year), although for one twin there was insufficient serum. The median inhibin-A level in the twin pregnancies was 1.99 multiples of the median (MOM) for singleton pregnancies (P < 0.001) [95 per cent confidence interval (CI) 1.83-2.16]. These results enable inhibin-A values to be adjusted so that prenatal screening for Down's syndrome can be performed using this marker in twin pregnancies as well as in singleton pregnancies.

Maternal serum inhibin-A in pregnancies with insulin-dependent diabetes mellitus: implications for screening for Down's syndrome

A nested case-control study using stored serum samples collected as part of a prospective study of the outcome of pregnancy was performed to investigate concentrations of (dimeric) inhibin-A in maternal serum between 15 and 22 weeks of pregnancy in 126 pregnancies among 92 women with insulin-dependent diabetes mellitus (IDDM). Each IDDM pregnancy was matched with two control singleton pregnancies for gestational age (same completed week) and duration of sample storage (same calendar quarter). The median inhibin-A level in the IDDM pregnancies was 0.88 multiples of the median (MOM) for pregnancies without IDDM at the same gestational age (P = 0.05) (95 per cent confidence interval 0.78-1.00) or 0.91 MOM after adjustment for maternal weight. These results enable inhibin-A values to be adjusted so that prenatal screening for Down's syndrome can be performed using this marker in IDDM pregnancies as well as in non-diabetic pregnancies.

Second trimester levels of maternal serum inhibin A, total inhibin, alpha inhibin precursor, and activin in Down's syndrome pregnancy

OBJECTIVE

To determine the levels of various biochemical forms of the placental protein, inhibin (total inhibin, inhibin A, and alpha inhibin precursor) and activin in maternal serum samples from fetal Down's syndrome, and to determine which of these analytes most effectively identifies samples from affected pregnancies.

METHODS

Maternal serum samples were collected from 100 unaffected pregnancies and 20 cases of fetal Down's syndrome during gestational weeks 15-20 for routine triple marker screening, and were stored frozen after clinical assay. Levels of inhibin A, total inhibin, alpha inhibin precursor (pro-alphaC), and activin were compared retrospectively in the Down's syndrome cases and control samples.

RESULTS

There was no association of the inhibin or activin levels with gestational age or length of freezer storage, and therefore single median values were determined for the unaffected pregnancies for each analyte. Multiples of the unaffected median (MoM) values were calculated for all cases, showing that inhibin A (1.95 MoM) provided the best discrimination between cases and controls, followed by total inhibin (1.37 MoM). Mann-Whitney U analysis showed significant group differences in inhibin A (P = 0.0001) and total inhibin (P = 0.0005). In contrast, alpha inhibin precursor (0.81 MoM) and activin (1.16 MoM) levels in Down's syndrome cases were not significantly different from those in unaffected patients.

CONCLUSIONS

Levels of inhibin A and total inhibin, but not alpha inhibin precursor or activin, are significantly raised in maternal serum from cases of fetal Down's syndrome. These data, taken together, indicate that inhibin A levels are specifically raised in Down's syndrome pregnancy. 45% of the inhibin A levels in the Down's syndrome samples were above the 90th centile of unaffected levels, indicating that inhibin A may be as good a marker as human chorionic gonadotrophin, the most informative serum marker currently in use.

Dimeric inhibin A as a marker for Down's syndrome in early pregnancy

BACKGROUND

In screening for Down's syndrome in the second trimester of pregnancy, the concentrations of alpha-fetoprotein, the beta subunit of human chorionic gonadotropin, and intact human chorionic gonadotropin in material serum are widely used markers. We investigated a new marker, dimeric inhibin A, and compared its predictive value with that of the established markers.

METHODS

Serum samples were obtained at 7 to 18 weeks of gestation from 58 women whose fetuses were known to be affected by Down's syndrome, 32 whose fetuses were affected by trisomy 18, and 438 whose fetuses were normal, and the samples were analyzed for each marker. Individual serum concentrations of each marker were converted to multiples of the median value at the appropriate length of gestation in the women with normal pregnancies, and rates of detection of Down's syndrome by screening for inhibin A in various combinations with the other markers were estimated by multivariate analysis.

RESULTS

In the women with fetuses affected by Down's syndrome, the serum inhibin A concentrations were 2.06 times the median value in the women with normal pregnancies (P < 0.001). This compared with 2.00 times the median for the beta subunit of human chorionic gonadotropin, 1.82 times the median for intact human chorionic gonadotropin, and 0.72 for alpha-fetoprotein. The serum concentrations of inhibin A in the women with fetuses affected by Down's syndrome did not appear to be significantly elevated above normal until the end of the first trimester and were not significantly different from normal in the women with fetuses affected by trisomy 18 (P = 0.17). The rate of detection of Down's syndrome was 53 percent and the false positive rate was 5 percent when alpha-fetoprotein, the beta subunit of human chorionic gonadotropin, the maternal age were used together as predictors. The detection rate increased to 75 percent when inhibin A was added (P = 0.002).

CONCLUSIONS

In the second trimester of pregnancy, measuring inhibin A in maternal serum, in combination with measurements of alpha-fetoprotein and beta subunit of human chorionic gonadotropin, significantly improved the rate of detection of Down's syndrome.

Prenatal screening for Down's syndrome using inhibin-A as a serum marker

The value of measuring inhibin-A (a beta A dimer) with human chorionic gonadotrophin (total or the sub-units free a-hCG and free beta-hCG separately), alpha-fetoprotein (AFP), and unconjugated oestriol (uE3) was examined to determine the effect on the performance of serum screening for Down's syndrome between 15 and 22 weeks of pregnancy. The study was based on stored serum samples from 77 Down's syndrome singleton pregnancies and 385 unaffected singleton pregnancies, matched for maternal age, gestational age, and duration of storage of the sample, supplemented by data from 970 white women with unaffected pregnancies. Inhibin-A was elevated in the serum of women with Down's syndrome pregnancies with a median of 1.79 multiples of the median (MOM). Using the four serum markers AFP, uE3, total hCG, and inhibin-A, in addition to maternal age, 70 per cent of Down's syndrome pregnancies were detected for a 5 per cent false-positive rate compared with 59 per cent with the conventional triple test (AFP, uE3, and total hCG with maternal age). If the estimate of gestational age were based on an ultrasound scan examination, the detection rate would be 77 per cent [95 per cent confidence interval (CI) 69-85 per cent] using the four serum markers including inhibin-A, compared with 67 per cent with the triple test or 79 per cent (95 per cent CI 71-87 per cent) if marker values were adjusted for maternal weight. If the detection rate were kept at 70 per cent and the gestational age were estimated by an ultrasound scan examination, the four-marker test would reduce the false-positive rate from 6-1 per cent using the triple test to 2-9 per cent. The results were virtually the same if free beta-hCG was used instead of total hCG. The inhibin-A-based four-marker test is the most effective method of prenatal screening for Down's syndrome suitable for routine use. If the extra cost required to carry out the inhibin-A test were less than about [symbol: see text]3 per woman screened, the four-marker test including inhibin-A would be financially cost-effective.