The "genetic sonogram": comparison of the index scoring system with the age-adjusted US risk assessment

Meta-analysis of validity of echogenic intracardiac foci for calculating the risk of Down syndrome in the second trimester of pregnancy

Echogenic intracardiac foci are a second trimester marker associated with aneuploidy in high-risk populations. The objective of this study is to assess the validity of echogenic intracardiac foci for Down syndrome detection in the second trimester ultrasound scan. A systematic search in major bibliographic databases was carried out (MEDLINE, EMBASE, CINAHL). Twenty-five studies about echogenic intracardiac foci were selected for statistical synthesis in this systematic review. Those 25 considered to be relevant were then subjected to critical reading, following the Critical Appraisal Skills Programme criteria, by at least three independent observers. Then, the published articles were subjected to a meta-analysis. A global sensitivity of 21.8% and a 4.1% false positive rate were obtained. The positive likelihood ratio was 5.08 (95% confidence interval, 4.04-6.41). The subgroups analysis did not reveal statistically significant differences. In conclusion, echogenic intracardiac foci as an isolated marker could be a tool to identify-rather than exclude-the high-risk group of Down syndrome, although it should be noted that it shows low sensitivity.

The history of imaging in obstetrics

During the past century, imaging of the pregnant patient has been performed with radiography, scintigraphy, computed tomography, magnetic resonance imaging, and ultrasonography (US). US imaging has emerged as the primary imaging modality, because it provides real-time images at relatively low cost without the use of ionizing radiation. This review begins with a discussion of the history and current status of imaging modalities other than US for the pregnant patient. The discussion then turns to an in-depth description of how US technology advanced to become such a valuable diagnostic tool in the obstetric patient. Finally, the broad range of diagnostic uses of US in these patients is presented, including its uses for distinguishing an intrauterine pregnancy from a failed or ectopic pregnancy in the first trimester; assigning gestational age and assessing fetal weight; evaluating the fetus for anomalies and aneuploidy; examining the uterus, cervix, placenta, and amniotic fluid; and guiding obstetric interventional procedures.

Noninvasive screening tools for Down syndrome: a review

Down syndrome is the leading cause of prenatal chromosome abnormalities, accounting for 53% of all reported chromosome conditions. Testing strategies, guidelines, and screening options have expanded from their conception in the 1970s, and now include such options as anatomical ultrasound, maternal serum screening, and noninvasive prenatal testing. This review summarizes all currently available noninvasive diagnostic techniques for the detection of Down syndrome. By understanding fully each technology and the possible alternatives, the physician will be able to provide their patients with all the information necessary to make an informed decision regarding their medical management.

Survey of prenatal counselling practices regarding aneuploidy risk modification, invasive diagnostic procedure risks, and procedure eligibility criteria in Canadian centres

OBJECTIVE

To explore prenatal practices related to aneuploidy screening, risk modification, and invasive diagnostic procedures across Canadian centres.

METHODS

We conducted a survey of members of the Canadian Association of Genetic Counsellors, the Canadian College of Medical Genetics, and the Canadian Society of Maternal Fetal Medicine, who provide direct counselling or management of prenatal patients in Canada.

RESULTS

Eighty-two of 157 respondents indicated that their centre's definition of advanced maternal age was ≥ 35 years, with 33/157 respondents reporting an advanced maternal age definition of ≥ 40 years. The majority of respondents reported that prenatal serum screening for aneuploidy is provincially funded in their province or territory (121/147). The majority of respondents who reported that prenatal screening is not provincially funded (17/147) were from Quebec (14/17). Thirty-nine of 123 respondents reported that their centre defines increased nuchal translucency as ≥ 3.0 mm, whereas 49/123 reported a definition of ≥ 3.5 mm. Sixty-four of 150 respondents reported that the aneuploidy risk provided by serum screening is modified by a soft marker likelihood ratio, whereas 46/150 respondents reported that both age-related and serum screening risks are modified. Fifty-nine of 124 respondents reported that their centre will modify aneuploidy risk after a normal ultrasound; the most commonly cited negative likelihood ratio was 0.5. The most commonly reported procedure-related risk for chorionic villus sampling was 1/100 (123/147) and for amniocentesis was 1/200 (73/142).

CONCLUSION

This study demonstrates inconsistencies in prenatal practices and access to screening programs across Canada. The information gained from this study will inform policy advisors developing prenatal practice guidelines at both the provincial and national levels.

Adjusted risk for trisomy 21 after the anomaly scan. How accurate is the Fetal Medicine Foundation algorithm?

PURPOSE

To examine the accuracy of the Fetal Medicine Foundation algorithm used to adjust the risk for trisomy 21 after ultrasound findings detected or not at the time of the anomaly scan.

METHODS

This was a retrospective study of all amniocenteses performed in a single centre, in singleton pregnancies, between 1998 and 2008. Maternal demographic characteristics, second-trimester ultrasound findings, indications for amniocentesis and karyotype results were reviewed. The algorithm introduced by the Fetal Medicine Foundation was used to calculate the patient specific risk for trisomy 21 using the age related background risk and anomaly scan findings. Expected trisomy 21 cases based on these risks was compared with the actual karyotype results.

RESULTS

Overall, 4,511 cases of singleton pregnancies that underwent second-trimester amniocentesis were reviewed. In 572 cases (12.7%), there were markers of chromosomal abnormality and no previous screening for trisomy 21. The expected number of trisomy 21 cases based on maternal age for this population of 572 cases was 1. The expected number of chromosomal abnormalities after adjusting for ultrasound findings based on the algorithm introduced by the Fetal Medicine Foundation was 6.9 (95% confidence interval 3.4-14.3). After karyotyping, in this population there were 6 cases of trisomy 21, 1 case of Trisomy 18 and 1 case of XXY.

CONCLUSIONS

The algorithm that adjusts the age related risk of trisomy 21 according to second-trimester anomaly scan findings is very accurate in predicting the modified risk.

The association of maternal BMI with fetal echogenic intracardiac foci and echogenic bowel

OBJECTIVES

To evaluate the impact of maternal body mass index (BMI) as well as maternal ethnicity on the detection of either echogenic intra-cardiac focus (EIF) or echogenic bowel (EB).

METHODS

This prospective study identified 74 uncomplicated singleton fetuses in which EIF and/or EB were detected between 18 and 21 weeks of gestation (i.e. study group). Seventy four consecutively scanned fetuses without EIF or EB, at the same gestational age, were selected as controls. The differences in maternal BMI and maternal ethnicity were compared between the two groups using the chi(2) test, Fisher's exact test, and the Student t-test. A multivariable logistic regression model was constructed to control for confounders. Odds ratios (OR) and their 95% confidence interval (CI) were computed.

RESULTS

The mean maternal BMI was significantly lower in the study group as compared to controls (22.9 +/- 3.1 vs. 28.0 +/- 7.5 kg/m(2), respectively; p < 0.0001). Patients with fetal EIF and/or EB were significantly more likely to be Asians (20.3% vs. 5.4%, OR = 4.5; 95% CI 1.3-16.9). Using a multivariable analysis, controlling for ethnicity, the association between maternal BMI and fetal EIF or EB remained significant (OR = 0.83; 95% CI 0.76-0.91). However, based on this model Asian ethnicity was not an independent risk factor for the detection of EIF and/or EB (OR = 2.6; 95% CI 0.8-8.9).

CONCLUSIONS

Our data suggests an inverse relationship between the maternal BMI and the detection of fetal EIF and/or EB. Moreover, it appears that low maternal BMI, and not Asian ethnicity, is an independent risk factor for the detection of these echogenic fetal findings.

Comparison of modes of ascertainment for mosaic vs complete trisomy 21

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

The second trimester genetic sonogram

The genetic sonogram, a fetal anatomic survey targeted at identifying features associated with aneuploidy, is carried out between 15 and 20 weeks' gestation. It has evolved as an adjunctive screening tool capable of further refining the individualized risk-calculation for trisomy that is based on maternal age or serum screening markers. The significance of a range of major structural anomalies and so-called "soft-markers" for trisomy, detected both in isolation and in combination, has been widely investigated. This review serves to describe the key components of the second trimester genetic sonogram and to illustrate how these markers are integrated into risk assessment for aneuploidy.

Ultrasound Findings After Screening for Down Syndrome Using the Integrated Test

OBJECTIVE

To evaluate the incidence and significance of fetal anomalies and "soft markers" after screening for Down syndrome using the integrated test.

METHODS

This study is a retrospective study of 2,332 women at University College London Hospitals, United Kingdom. All women were screened for Down syndrome by the integrated test. Subsequently, a detailed anomaly scan was performed. All scan reports and screening results were analyzed statistically using SPSS 11.0 software.

RESULTS

Sixty-eight (2.9%) patients were categorized as high risk. There were 12 cases affected by Down syndrome, 10 (10 of 68) in the high-risk group and two (two of 2,264) in the low-risk group. Soft markers or structural anomalies were found in 13.0% of the low-risk group, in 29.4% of the high-risk group, and in 50% of the fetuses affected by Down syndrome. Multiplying the likelihood ratio of each marker with the risk of Down syndrome from the integrated test reduced the false-positive rate of the integrated test from 2.5% to 1.8%, but was accompanied by a reduction in the detection rate from 83% to 75%.

CONCLUSION

Absence of structural anomalies or markers should not prevent offering karyotyping to women in the high-risk group, because this would result in a significant reduction in the detection rate of Down syndrome. Women screened as low risk by the integrated test who have isolated soft markers should not be offered an amniocentesis.

The risk of a major trisomy in fetuses with pyelectasis: the impact of an abnormal maternal serum screen or additional sonographic markers

OBJECTIVE

This study was undertaken to evaluate the contribution of either an abnormal second-trimester maternal serum screen or the presence of additional sonographic markers of aneuploidy to the risk of a major trisomy (13, 18, and 21) in fetuses with pyelectasis.

STUDY DESIGN

A retrospective review of a large amniocentesis database was performed. Specimens obtained after the sonographic detection of fetal pyelectasis were eligible for analysis. Age-matched women who underwent amniocentesis solely for maternal anxiety or advanced maternal age served as controls.

RESULTS

760,495 amniocentesis specimens were analyzed. Fetal pyelectasis was detected in 671 cases. Pyelectasis, with either a single or multiple additional sonographic markers, was associated with an 8-fold and 62-fold increase in the prevalence of major trisomies (odds ratio = 7.7, 95% CI = 1.2-32.6, P = 0.02) and (odds ratio = 61.9, 95% CI = 13.2-144.6, P < .001), respectively. Pyelectasis with an abnormal maternal serum screen, with or without additional sonographic markers, was associated with a 32-fold and a 205-fold increase in major trisomies (odds ratio = 32.2, 95% CI = 5.3-94.8, P < .001) and (odds ratio = 205.8, 95% CI = 37.9-427.6, P < .001), respectively.

CONCLUSION

In fetuses with pyelectasis, the presence of additional sonographic markers or an abnormal maternal serum screen significantly increases the risk of trisomy 13, 18, and 21.

Dépistage de la trisomie 21 en France: le consensus du pire

Down syndrome screening has been based on second trimester maternal serum markers assay for many years. Another late strategy was based on the "genetic sonogram" performed in early second trimester in high-risk populations selected on maternal age or second trimester maternal serum markers. New strategies for Down syndrome screening have emerged over the last 10 years, with higher sensitivity and lower false-positive rates. First trimester ultrasound examination is a successful screening test; the sensitivity of nuchal translucency measurement is of 60 to 77% for a 5% false-positive rate. Combining nuchal translucency measurement with PAPP-A and free beta-hCG assay (first trimester combined screening) increases the sensitivity up to 82%. The most specific strategy is based on the integrated test, i.e., the integration of the quadruple test performed in second trimester (inhibine dimeric A, total beta-hCG, AFP, and uE3 assay) to the first trimester combined screening: for a 85% detection rate, the false-positive rate is estimated to 0.9%. However, it is ethical only with the patient agreement because it prevents access to the results of first trimester combined screening, and deprives the patient of an early diagnosis by CVS. Therefore, alternative strategies were proposed: step-wise sequential screening and contingent sequential screening. In the step-wise screening, karyotype is offered when the result of the combined test is beyond a specified threshold. If the combined test result is below this threshold, quadruple test is offered, and the final risk is calculated in the second trimester by integrating the results of the quadruple test with those of the combined test. Contingent screening also begins with the first trimester-combined test. According to its results, the patients are considered in one of the 3 following risk groups: high, intermediate, or low risk. An early karyotype is proposed to the high-risk group after combined testing. The low risk group is reassured and thus the quadruple test is not performed. The quadruple test is proposed to the intermediate risk group and final risk is calculated by the integration of the combined test result into the quadruple test result. The global detection rate of the step-wise or contingent sequential screening is estimated to 84% for a false-positive rate of 2%.

Dépistage de la trisomie 21 par le test combiné du premier trimestre suivi par l'échographie du second trimestre en population générale

BACKGROUND

Recent studies have reported the efficacy of first trimester combined screening for Down Syndrome based on maternal age, serum markers (human chorionic gonadotropin, pregnancy-associated plasma protein A), and ultrasound measurement of fetal nuchal translucency. However, those do not incorporate the value of the widely accepted routine 20-22 week anomaly scan.

STUDY DESIGN

We carried out a multi-centre, interventional study in the unselected population of a single health authority in order to assess the performance of first trimester combined screening, followed by routine second trimester ultrasound examination and/or screening by maternal serum markers (free beta-hCG and alpha-fetoprotein measurement or total hCG, alpha-fetoprotein and unconjugated estriol measurement) when incidentally performed. Detection and screen positive rates were estimated using a correction method for non verified issues. A cost analysis was also performed.

RESULTS

During the study period, 14,934 women were included. Fifty-one cases of Down Syndrome were observed, giving a prevalence of 3.4 per 1000 pregnancies. Of these, 46 were diagnosed through first (N=41) or second (N=5) trimester screening. Among the 5 screen-negative Down syndrome cases, all were diagnosed postnatally after an uneventful pregnancy. Detection and screen positive rates of first trimester combined screening were 79.6% and 2.7%, respectively. These features reached 89.7 and 4.2%, respectively when combined with second trimester ultrasound screening. The average cost of the full screening procedure was 108 euro (120 $) per woman and the cost per diagnosed Down syndrome pregnancy was 7,118 euro (7,909 $).

CONCLUSION

Our findings suggest that one pragmatic interventional two-step approach using first-trimester combined screening followed by second trimester detailed ultrasound examination is a suitable and acceptable option for Down syndrome screening in pregnancy.

Prenatal Screening for Fetal Aneuploidy

This document has been archived because it contains outdated information. It should not be consulted for clinical use, but for historical research only. Please visit the journal website for the most recent guidelines.

Screening for Down syndrome using first-trimester combined screening followed by second-trimester ultrasound examination in an unselected population

OBJECTIVE

Recent studies have reported the efficacy of first-trimester combined screening for Down syndrome based on maternal age, serum markers (human chorionic gonadotropin, pregnancy-associated plasma protein A), and ultrasound measurement of fetal nuchal translucency. However, those do not incorporate the value of the widely accepted routine 20-22 weeks' anomaly scan.

STUDY DESIGN

We carried out a multicenter, interventional study in the unselected population of a single health authority in order to assess the performance of first-trimester combined screening, followed by routine second trimester ultrasound examination and/or screening by maternal serum markers (free beta-hCG and alpha-fetoprotein measurement or total hCG, alpha-fetoprotein, and unconjugated estriol measurement) when incidentally performed. Detection and screen positive rates were estimated using a correction method for nonverified issues. A cost analysis was also performed.

RESULTS

During the study period, 14,934 women were included. Fifty-one cases of Down syndrome were observed, giving a prevalence of 3.4 per 1000 pregnancies. Of these, 46 were diagnosed through first (n = 41) or second (n = 5) trimester screening. Among the 5 screen-negative Down syndrome cases, all were diagnosed postnatally after an uneventful pregnancy. Detection and screen positive rates of first-trimester combined screening were 79.6% and 2.7%, respectively. These features reached 89.7%, and 4.2%, respectively, when combined with second-trimester ultrasound screening. The average cost of the full screening procedure was 108 euros (120 dollars) per woman and the cost per diagnosed Down syndrome pregnancy was 7,118 euros (7909 dollars).

CONCLUSION

Our findings suggest that 1 pragmatic interventional 2-step approach using first-trimester combined screening followed by second-trimester detailed ultrasound examination is a suitable and acceptable option for Down syndrome screening in pregnancy.

Normal obstetric ultrasound reduces the risk of Down syndrome in fetuses of older mothers

The objective of this study is to determine whether a normal fetal morphology ultrasound scan in women older than 35 years reduces the risk of aneuploidy. We reviewed the results of amniocentesis and second trimester sonogram in all women older than 35 years from 1991 to 1995. None had prior screening. We excluded fetuses with structural anomalies. We determined the sensitivity and specificity of minor markers in detecting Down syndrome and also determined the reduction in risk of a normal sonogram. Among the 2060 women older than 35 years giving birth during the study period, 16 (0.78%) delivered an infant with Down syndrome. Of the 16 fetuses, two had no prenatal testing or ultrasound, two had invasive testing but no second trimester sonogram, five had a normal sonogram and seven had one or more sonographic markers of Down syndrome. At least 17% of women older than 35 years did not participate in prenatal testing or ultrasound. Ultrasound detected Down syndrome with a sensitivity of 59% (95% confidence interval: 45-72%), a false-positive rate of 10.6% (9.4-11.8%) and a positive predictor value of 1 in 9. The likelihood of having normal karyotype if the sonogram was normal was 0.46 (0.31-0.61). In women older than 35 years, a normal second trimester sonogram reduces the risk of Down syndrome by more than 50%. At least 17% of women older than 35 years do not participate in prenatal testing or ultrasound.

The role of the second trimester genetic sonogram in screening for fetal Down syndrome

The Genetic Sonogram is an ultrasound examination done on second trimester fetuses that not only evaluates the fetus for structural malformations, but also searches for the sonographic markers of fetal Down syndrome. The main markers that comprise the genetic sonogram include the nuchal fold, short femur and humerus, pyelectasis, hyperechoic bowel, echogenic intracardiac focus, and any major abnormality. The absence of any marker on a second trimester scan conveys a 60-80% reduction in prior risk of Down syndrome based on advanced maternal age or serum screen risk. The presence of sonographic markers, either singly or in combination, will raise the baseline risk of Down syndrome using likelihood ratios calculated for each individual marker. Using this approach, approximately 75% of fetuses with Down syndrome can be identified by modifying the patient's baseline risk according to the results of the ultrasound. The second trimester scan will likely continue to play an important role in the future in the detection of aneuploidy.

The impact of gestational age on the sonographic detection of aneuploidy

OBJECTIVE

The purpose of this study was to identify the influence of gestational age on the detection of sonographic markers of aneuploidy.

STUDY DESIGN

Using a retrospective chart review, cases of trisomy 13, 18, and 21 with fetal ultrasounds between 14 1/7 and 36 4/7 weeks' gestation were identified. Sonographic markers were subdivided into major abnormalities and "soft" sonographic markers: nuchal thickening > or = 5 mm, humerus or femur length <10th percentile, intracardiac echogenic focus, echogenic bowel, pyelectasis > or = 4 mm, and choroid plexus cysts. Markers were stratified by karyotype and gestational age.

RESULTS

Fifteen fetuses with trisomy 13, 32 with trisomy 18, and 49 with trisomy 21 were identified. There was no difference in the prevalence of ultrasound markers by gestational age (P = .40). Soft markers were more common in the second trimester of pregnancy (P = .006) with a trend toward increased prevalence of major anomalies with advancing gestation (P = .22).

CONCLUSION

Although sonographic markers change with gestational age, these markers are present throughout gestation and can provide clinically useful information to guide patient counseling.

Economic modelling of antenatal screening and ultrasound scanning programmes for identification of fetal abnormalities

OBJECTIVE

Within the framework of a health technology assessment and using an economic model, to determine the most clinically and cost effective policy of scanning and screening for fetal abnormalities in early pregnancy.

DESIGN

A discrete event simulation model of 50,000 singleton pregnancies.

SETTING

Maternity services in Scotland.

POPULATION

Women during the first 24 weeks of their pregnancy.

METHODS

The mathematical model was populated with data on uptake of screening, prevalence, detection and false positive rates for eight fetal abnormalities and with costs for ultrasound scanning and serum screening. Inclusion of abnormalities was based on the relative prevalence and clinical importance of conditions and the availability of data. Six strategies for the identification of abnormalities prenatally including combinations of first and second trimester ultrasound scanning and first and second trimester screening for chromosomal abnormalities were compared.

MAIN OUTCOME MEASURES

The number of abnormalities detected and missed, the number of iatrogenic losses resulting from invasive tests, the total cost of strategies and the cost per abnormality detected were compared between strategies.

RESULTS

First trimester screening for chromosomal abnormalities costs more than second trimester screening but results in fewer iatrogenic losses. Strategies which include a second trimester ultrasound scan result in more abnormalities being detected and have lower costs per anomaly detected.

CONCLUSIONS

The preferred strategy includes both first and second trimester ultrasound scans and a first trimester screening test for chromosomal abnormalities. It has been recommended that this policy is offered to all women in Scotland.

Ultrasound screening of fetuses at increased risk for Down syndrome: how many missed diagnoses?

OBJECTIVE

To determine the number of Down syndrome (DS) fetuses identified, amniocenteses performed, and procedure-related losses incurred when second-trimester ultrasound is used to screen high-risk patients in order to determine who should undergo an amniocentesis.

METHODS

A decision analytic model was designed for women at increased risk for a DS fetus due to either advanced maternal age (AMA) or a positive expanded maternal serum alpha fetoprotein (MSAFP) screening test, also known as a triple screen (+triple) test. The model compared: (1) the current standard of offering all at-risk women amniocentesis to (2) a policy of performing amniocentesis only when sonographic markers of DS are seen on ultrasound. Baseline assumptions included a sensitivity of 60.6% for targeted ultrasound and a screen-positive rate of 16.2%.

RESULTS

If targeted ultrasound is used to determine whether high-risk patients should undergo amniocentesis, 56% (3933/7025) of all DS fetuses are missed. The diagnosis of DS is missed most frequently among women at highest risk for DS (AMA and +triple). In this subgroup of patients, there are 3152 DS fetuses in the second trimester, of which 2815 (89%) are identified by triple screen test. When an ultrasound screen is added, only 1709 (54%) of DS fetuses will be identified.

CONCLUSION

Substantially fewer DS fetuses will be detected when targeted ultrasound is used as a screen among already identified high-risk patients.

Cost-effectiveness model for first-trimester versus second-trimester ultrasound screening for down syndrome

PURPOSE

To develop a cost-effectiveness analysis model from the perspective of Medicare reimbursement to evaluate the costs and potential risks involved in performing second-trimester genetic sonography following the first-trimester sonographic measurement of nuchal translucency and serology for Down syndrome screening.

METHODS

Three clinical screening algorithms were constructed that detailed the diagnostic evaluation of the target population by using first-trimester or second-trimester ultrasound and appropriate serologies or first-trimester and second-trimester screening in combination. The cost analysis was then created by using a computer spreadsheet program by applying Medicare reimbursement, the prevalence of Down syndrome, and reported sensitivities of first-trimester and second-trimester ultrasound and analytes for Down syndrome for each clinical algorithm. Medicare Current Procedural Terminology codes, total relative value units, and payments for first-trimester and second-trimester ultrasound, chorionic villous sampling, amniocentesis, and serum analytes were obtained from the Medicare Part B Washington 2002 Provider Disclosure Report.

RESULTS

At any given prevalence of Down syndrome, first-trimester screening is always slightly less expensive to society than the other two models for both total cost and cost to diagnose each case of Down syndrome. Even if second-trimester screening were 100% sensitive, the sensitivity of first-trimester screening would have to fall below 55% for model 2 to be cheaper than model 1. Combining both first-trimester and second-trimester screening was substantially more expensive than models 1 or 2. More iatrogenic fetal deaths occur with combined screening than with either first or second trimester screening alone.

CONCLUSIONS

Screening using first-trimester ultrasound and serologic markers to screen for Down syndrome is always slightly less expensive to society than second-trimester serologic and ultrasound screening. However, there is a significantly increased risk for iatrogenic fetal death if second-trimester genetic sonography is performed following normal first-trimester screening using currently accepted risk ratios. Patients should be counseled appropriately with this information, because an individual's circumstances will affect that person's perception of risk and subsequently affect his or her decision making.

Genetic sonography: an option for women of advanced maternal age with negative triple-marker maternal serum screening results

OBJECTIVE

To determine whether offering genetic sonography to patients 35 years of age and older with negative maternal serum triple-marker screening results will result in an increase in the detection rate of trisomy 21.

METHODS

The detection rate of trisomy 21 was determined in women 35 years of age and older whose pregnancies were managed according to the following 3 policies: policy I, universal amniocentesis; policy II, maternal serum triple-marker screening followed by amniocentesis only in high-risk women (risk >1:190); and policy III, genetic sonography in women with negative maternal serum screening results (policy II). Policy III included the offering of genetic amniocentesis to patients with abnormal genetic sonographic findings. The rate of acceptance of genetic amniocentesis was modeled, as was the sensitivity (50%-90%) and false-positive rate (5%-25%) of genetic sonography.

RESULTS

The number of fetuses expected to have trisomy 21 was 784. For patients evaluated under policy II, 86.3% of fetuses with trisomy 21 were detected. On the basis of the detection rate for trisomy 21 of policy II, the addition of fetuses with trisomy 21 identified under policy III was significantly (P < .01) increased (93.2% to 98.6%) for genetic sonographic sensitivities ranging between 50% and 90%.

CONCLUSIONS

A policy of offering genetic sonography followed by amniocentesis to patients 35 years of age and older who originally had triple-marker maternal serum screening findings that were negative for the diagnosis of trisomy 21 results in a higher overall detection rate of trisomy 21.

The Genetic Sonogram Scoring Index

This article describes the individual sonographic markers used in the Genetic Sonogram Scoring Index. The importance of the clustering of markers forms the basis of the scoring index, such that individual markers are assigned point values based on their sensitivity and specificity in the detection of Down syndrome. The points acquired by each fetus are tabulated into a final "score." The performance of the scoring index in the detection of aneuploidy is presented. The clinical application of the scoring index for the detection of chromosomally abnormal fetuses in patients both at high- and low-risk for aneuploidy is discussed.

Is genetic ultrasound cost-effective?

During the past 10 years, investigators have reported studies examining the potential of second-trimester genetic sonography to identify fetuses at risk for trisomy 21. The consensus among most investigators is that genetic sonography offers an alternative to universal amniocentesis in high-risk women and lowers the loss rate of normal fetuses subjected to amniocentesis because of risk factors associated with advanced maternal age or abnormal maternal-serum screening. Although there is now consensus that genetic sonography may be a useful screening tool, there has been a paucity of data regarding its cost-effectiveness. In this review, 3 studies are examined and cost-effectiveness of genetic sonography evaluated. The first study compared genetic sonography and universal amniocentesis and found that genetic sonography was cost-effective if the sensitivity is 75% or higher, resulted in a savings to the healthcare system of 9%, and decreased the loss rate of normal fetuses following amniocentesis by 87%. The second study examined the use of genetic sonography in women less than 35 years of age who underwent maternal-serum triple-marker serum screening. Women who were screen negative but who were classified as moderate risk for trisomy 21 (risk 1:191 to 1:1,000) were offered genetic sonography. Amniocentesis was offered only if the genetic sonogram was abnormal. The study demonstrated that the use of genetic sonography in this group of patients increased the detection rate of trisomy 21, was cost effective, and was a safe procedure. The third study examined the use of genetic sonography in women 35 years of age and older who declined amniocentesis following second-trimester genetic counseling. Genetic sonography was offered to this group of patients followed by amniocentesis if an abnormal ultrasound finding was present. The data were analyzed for various acceptance rates of amniocentesis by the patient when informed of the ultrasound findings. Examination of the data demonstrated this approach increased the detection rate of trisomy 21, was cost-effective, and was a safe procedure. In conclusion, genetic sonography when applied in the above clinical settings is cost-effective, results in a higher detection rate of trisomy 21, and is safe procedure.

Use of genetic sonography for adjusting the risk for fetal Down syndrome

Systematic evaluation of ultrasound findings known to be associated with trisomy 21, at an appropriate gestational age, has been referred to as a genetic sonogram. A number of high-risk centers performing genetic sonography have reported detection of ultrasound abnormalities in the majority of fetuses with fetal Down syndrome. However, nonspecific markers are more commonly observed than structural abnormalities, which are detected in less than 20% of cases in a nonselected population. Also, the actual sensitivity of a genetic sonogram will depend on various factors including the markers sought, gestational age, reasons for referral, and of course the quality of the ultrasound. Appropriate use of a genetic sonogram can help to modify the risk of fetal Down syndrome by decreasing the risk when the ultrasound is normal, or increasing the risk when specific ultrasound markers are detected. The postultrasound risk can be estimated by applying specific likelihood ratios, reflecting the strength of individual markers, with the a priori risk based on maternal age alone, or combined with biochemical markers when known. We review this approach of age-adjusted ultrasound risk assessment for fetal Down syndrome and illustrate how the risk can be estimated. Individual sonographic markers are also discussed.

The genetic sonogram: a method of risk assessment for Down syndrome in the second trimester

OBJECTIVE

To determine the risk of Down syndrome in fetuses with sonographic markers using the Bayes theorem and likelihood ratios.

METHODS

We prospectively evaluated the midtrimester sonographic features of fetuses with Down syndrome and compared them with euploid fetuses. Patients were referred for an increased risk of aneuploidy and evaluated for the presence of structural defects, a nuchal fold, short long bones, pyelectasis, an echogenic intracardiac focus, and hyperechoic bowel. All fetuses underwent amniocentesis at the time of sonographic assessment. The sensitivity, specificity, and likelihood ratios for markers were calculated both as nonisolated and isolated findings.

RESULT

There were 164 fetuses with Down syndrome and 656 euploid fetuses. The presence of any marker resulted in sensitivity for the detection of Down syndrome of 80.5% with a false-positive rate of 12.4%. The absence of any markers conferred a likelihood ratio of 0.2, decreasing the risk of Down syndrome by 80%. As an isolated marker, the nuchal fold had an "infinite" likelihood ratio for Down syndrome; a short humerus had a likelihood ratio of 5.8, whereas structural anomalies had a likelihood ratio of 3.3. Other isolated markers had low likelihood ratios because of the higher prevalence in the unaffected population. The likelihood ratios for the presence of 1, 2, and 3 of any of the markers were 1.9, 6.2, and 80, respectively.

CONCLUSIONS

Although an isolated marker with a low likelihood ratio may not increase a patient's risk of Down syndrome, the presence of such a marker precludes reducing the risk of aneuploidy. Clusters of markers appear to confer a higher risk.

Genetic sonography: a cost-effective method for evaluating women 35 years and older who decline genetic amniocentesis

OBJECTIVE

To determine whether offering genetic sonography to patients who decline invasive testing can increase the detection rate of trisomy 21 and is cost-effective.

METHODS

The detection rate of trisomy 21, the number of pregnancy losses after amniocentesis, and the cost of detecting a single fetus with trisomy 21 were determined in women 35 years and older managed according to the following 3 policies: (1) universal amniocentesis, (2) genetic counseling for maternal age-associated risks for trisomy 21 followed by amniocentesis in patients who elected it, and (3) genetic counseling followed by genetic sonography in patients who originally declined genetic amniocentesis.

RESULT

From a population of 40,143 women 35 years and older, the expected number of trisomy 21 fetuses was 349. After genetic counseling, 32% of patients declined invasive testing, resulting in detection of 70% of fetuses with trisomy 21. For universal amniocentesis, the cost to detect 1 fetus with trisomy 21 was $138,036. For the 32% who declined invasive testing after genetic counseling and underwent genetic sonography, the cost to detect a single fetus with trisomy 21 was a function of sensitivity and the screen-positive rate. For screen-positive rates between 5% and 25%, genetic sonography resulted in a cost savings between 14.3% and 18.8% when compared with universal invasive testing and resulted in a considerable increase in detection of fetuses with trisomy 21 (77% to 97%).

CONCLUSIONS

A policy of offering genetic sonography followed by amniocentesis to patients 35 years and older who originally decline invasive testing for the diagnosis of trisomy 21 is cost-effective and results in a higher overall detection rate for trisomy 21 without an increased risk of pregnancy loss.