Measurement of Nuchal Translucency and the Prenatal Diagnosis of Down Syndrome

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

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

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.

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.

Contingent non-invasive prenatal testing: an opportunity to improve non-genetic aspects of fetal aneuploidy screening

BACKGROUND

Several countries today struggle with suboptimal performances in many aspects of the fetal aneuploidy screening process and consider introducing non-invasive prenatal screening (NIPT) as a solution. In this study, costs and benefits of different scenarios for contingent NIPT screening in Belgium are evaluated with respect to partial redistribution of the national screening budget into quality improving measures for those screening activities that will be maintained when full NIPT screening is implemented.

METHODS

Data from the Belgian National Institute for Health and Disability Insurance and the Study Centre for Perinatal Epidemiology were used in modeled calculations of medical and economic impact of NIPT after prior conventional screening (1) at thresholds 1:300 and 1:600, and (2) at current and improved screening sensitivity.

RESULTS

Contingent NIPT screening under current screening conditions would maintain today's 7.9(0)/000 live birth prevalence of Down syndrome (LBPD) at an 11% reduction of overall short-term costs. Lowering the screening threshold to 1:600 or increasing sensitivity by 10% would reduce LBPD to 7(0)/000 at a maximum 3% increase of overall short-term costs.

CONCLUSION

Today, in Belgium and in many other countries, full NIPT screening is considered too expensive for immediate introduction into the national fetal aneuploidy screening program. Contingent NIPT screening is both clinically and economically beneficial. A temporary contingent NIPT protocol allows for reinvesting economic savings into optimization of those screening aspects, which are to be maintained in parallel to full NIPT screening.

Do the Levels of Maternal Plasma Trace Elements Affect Fetal Nuchal Translucency Thickness?

OBJECTIVE

Fetal nuchal translucency (NT) thickness is an important marker for prenatal screening; however, studies focusing on the correlation between maternal trace element levels and NT thickness are limited. The aim of this study was to evaluate maternal trace element levels during the first trimester and to investigate the association between maternal trace element levels and fetal NT thickness.

METHODS

In total, 113 samples were obtained from singleton pregnant women. Maternal plasma samples were collected in the first trimester of gestation. Plasma trace element levels were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Nuchal translucency thickness was measured using ultrasonography at 10-14 weeks of gestation.

RESULTS

We found that maternal plasma potassium (K) levels had a significant negative correlation with both NT (r = -0.230, p < 0.05) and NT Multiples of the Median (NT MoM) (r = -0.206, p < 0.05). After adjustment for potential confounders, log-transformed maternal plasma potassium levels in the first trimester were significantly associated with fetal NT (NT MoM: β = -0.68, p < 0.05; NT: β = -1.20, p < 0.01). Although not statistically significant, the As, Hg and Pb levels in maternal plasma were positively correlated with NT, and the Mg, Cu, Zn, Na and Ca levels were negatively correlated with NT.

CONCLUSION

Maternal plasma K levels during the first trimester appeared to be associated with NT thickness. The essential elements tended to decrease NT thickness, and non-essential elements tended to increase it.

Introducing the non-invasive prenatal test for trisomy 21 in Belgium: a cost-consequences analysis

BACKGROUND

The first- and second-trimester screening for trisomy 21 (T21) are reimbursed for all pregnant women in Belgium. Using a cut-off risk of 1:300 for T21, about 5% of all pregnant women are referred for definitive prenatal diagnosis using an invasive test, at a sensitivity of (only) 72.5%. The sensitivity and specificity of the non-invasive prenatal test (NIPT) are over 99% but come at a cost of €460 (£373) per test. The objective is to estimate the consequences of introducing NIPT for the detection of T21.

METHODS

A cost-consequences analysis was performed presenting the impact on benefits, harms and costs. Context-specific real-world information was available to set up a model reflecting the current screening situation in Belgium. This model was used to construct the second and first line NIPT screening scenarios applying information from the literature on NIPT's test accuracy.

RESULTS

Introducing NIPT in the first or second line reduces harm by decreasing the number of procedure-related miscarriages after invasive testing. In contrast with NIPT in the second line, offering NIPT in the first line additionally will miss fewer cases of T21 due to less false-negative test results. The introduction of NIPT in the second line results in cost savings, which is not true for NIPT at the current price in the first line. If NIPT is offered to all pregnant women, the price should be lowered to about €150 to keep the screening cost per T21 diagnosis constant.

CONCLUSIONS

In Belgium, the introduction and reimbursement of NIPT as a second line triage test significantly reduces procedure-related miscarriages without increasing the short-term screening costs. Offering and reimbursing NIPT in the first line to all pregnant women is preferred in the long term, as it would, in addition, miss fewer cases of T21. However, taking into account the government's limited resources for universal reimbursement, the price of NIPT should first be lowered substantially before this can be realised.

Effects of period of gestation and position of fetal neck on nuchal translucency measurement

OBJECTIVE

The aim of this study was to determine the effects of period of gestation and position of fetal neck on nuchal translucency measurement.

MATERIALS AND METHODS

Nuchal translucency was measured in the mid-sagittal plane, with the fetal neck in the flexed, neutral, and extended positions in 100 pregnant women between 11 and 13(+6) weeks. Mean nuchal translucency measurements at different periods of gestation were compared. Differences between the extended and neutral positions (Δ extended nuchal translucency) and those between the flexed and neutral positions (Δ flexed nuchal translucency) were calculated. The repeatability coefficients for the measurements in all the three positions were computed. Statistical analysis was also done.

RESULTS

Nuchal translucency values were 1.050 ± 0.282 mm in the 11th week, 1.243 ± 0.348 mm in the 12th week, and 1.823 ± 0.357 mm in the 13th week (r = 0.747, p < 0.0001). The mean Δ flexed value was 0.233 ± 0.133 mm lesser than the neutral value (p < 0.0001). The mean Δ extended nuchal translucency was 0.305 ± 0.155 mm greater than the neutral value (p < 0.0001). The repeatability coefficient was the lowest in the neutral position (0.17 mm in the neutral position, 0.28 in the flexed position and 0.41 mm in the extended position).

CONCLUSION

We concluded that the period of gestation and fetal neck position can make a significant difference to nuchal translucency measurement. Repeatability of measurement is more accurate with the fetal neck in the neutral position. These findings have important implications for clinicians using nuchal translucency to screen the obstetric population for Down's syndrome.

Prenatal ultrasonographic measurement of the fetal iliac angle during the first and second trimester of pregnancy

OBJECTIVES

The aim of this study was to present our results of the sonographic measurement of the fetal iliac angle during the first and second trimesters of pregnancy.

METHODS

A total of 2168 fetal iliac angle measurements were performed in a transverse section of the fetal pelvis. The iliac angle measurements were compared in fetuses with trisomy 21 (n = 52) and fetuses with normal karyotype (n = 1980). The sensitivity, specificity, positive predictive value, negative predictive value and false positive rate in trisomy 21 fetuses were compared for multiple cut-off value. Statistical significance for measurements was estimated for trisomy 21.

RESULTS

A total of 2064 fetuses had adequate images for satisfactory measurement of the iliac wing angle and 1831 patients asked for a genetic invasive procedure. Of the fetuses with chromosomal aberrations, only the fetuses with trisomy 21 were included in the investigation. The risk of trisomy 21 in our population was 1 of 39. In the euploid fetuses, the mean iliac wing angle was 63.72°. The mean iliac wing angle in the fetuses with trisomy 21 was 90.32°, significantly higher than those seen in fetuses with normal karyotype.

CONCLUSION

The proven larger iliac wing angle in neonates with Down syndrome can be demonstrated sonographically during the pregnancy, especially in the first and second trimesters. This marker may be useful in prenatal screening or exclusion of trisomy 21.