The use of second-trimester genetic sonogram in guiding clinical management of patients at increased risk for fetal trisomy 21

Timing of ultrasound in pregnancy--how often? At what intervals?

The second trimester fetal anatomic survey has continued to evolve over the past 27 years. This review will summarize the changes in the anatomic survey that have occurred and provide recommendations that serve to improve compliance with the components of the survey. In order to provide clarity and direction, the goals and limitations of the second trimester fetal anatomic survey should be defined. The visualization rate of specific fetal anatomic structures can be increased by specifying acceptable, alternative views. A single follow-up examination within 2-4 weeks of a fetal anatomic survey or before 22 weeks' gestation should be offered when specific components of the fetal anatomic survey cannot be visualized. The fetal anomalies that the anatomic survey seeks to identify should be defined along with an acceptable detection rate.

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.

Role of fetal echocardiography in stepwise sequential screening for chromosomal disorders (combined test associated with modified genetic sonography)

OBJECTIVES

To evaluate the contribution made by fetal echocardiography in identifying Down's syndrome (DS) and other chromosomal disorders in a stepwise sequential screening method (first step: combined test (CT), second step: modified genetic sonography (MGS) (major malformation and nuchal fold)), for DS in the general population of pregnant women.

METHODS

Prospective study. During a 5-year study period (July 2005-June 2010) 17,911 pregnant women underwent CTs with MGS (with fetal cardiac morphological evaluation performed by obstetricians in a tertiary hospital) as a screening method for DS. We evaluated the sensitivity and false positive rate (FPR) (95% confidence interval (CI)) of three screening methods for DS and all chromosomal disorders: CT, CT + MGS, and CT + fetal echocardiography.

RESULTS

A total of 17,911 cases were analyzed with 67 chromosome disorders and 45 DS cases being found. For DS, the CT sensitivity was 80% (95% CI; 68.3-91.7) (36/45) and 79.1% (95% CI; 69.4-88.8) (53/67) for all chromosome disorders, with a FPR of 4.2% (95% CI; 3.9-4.5) (752/17,866) and 4.1% (95% CI; 3.8-4.4) (735/17,844), respectively. For CT + MSG and CT + fetal echocardiography, the sensitivity for DS was 93.3% (95% CI; 85.9-0.99) (42/45) and 95.5% (95% CI; 90.5-0.99) (64/67) for all chromosome disorders. The FPR for CT + MSG was 4.8% (95% CI; 4.5-5.1) (860/17,866) and 4.6% (95% CI; 4.3-4.9) (836/17,844), respectively. The FPR of CT + fetal echocardiography was 4.4% (95% CI; 4.1-4.7) (792/17,866) for DS screening and 4.3% (95% CI; 4-4.6) (770/17,844) for chromosome abnormality screening.

CONCLUSIONS

Fetal echocardiography is highly capable of identifying DS and other chromosomal disorders as a part of genetic sonography in stepwise sequential screening.

The quantitative lung index (QLI): a gestational age-independent sonographic predictor of fetal lung growth

OBJECTIVE

We sought to develop a gestational age-independent sonographic parameter to characterize lung growth.

STUDY DESIGN

Reported descriptors of lung growth, including lung-to-head circumference (HC) ratio (LHR) and observed/expected LHR, were examined. A new index, the quantitative lung index (QLI) was derived using published data on HC and the area of the base of the right lung.

RESULTS

Neither the LHR nor the observed/expected LHR proved to be gestational age independent. Right lung growth can be expressed using the following formula: QLI = lung area/(HC/10)^2. The 50th percentile of the QLI remained constant at approximately 1.0 for the gestational age between 16-32 weeks. A small lung (<1st percentile) was defined as a QLI <0.6.

CONCLUSION

Fetal right lung growth can be adequately described using the QLI, independent of gestational age. Further studies are needed to assess the clinical accuracy of the QLI in characterizing fetal right lung growth.

The history of the second-trimester sonographic markers for detecting fetal Down syndrome, and their current role in obstetric practice

This review summarizes the development, history and use of second-trimester sonographic markers for the detection of fetal Down syndrome over three decades. Starting with the nuchal fold thickening in 1985 and culminating in the genetic sonogram in the 1990 s. The combination of second-trimester serum screening with the ultrasound markers improved the detection rate of affected fetuses but also allowed patients to decrease their risk of carrying a fetus with Down syndrome if the genetic sonogram was normal. More recently the role of the genetic sonogram and its markers have changed with the wide spread use of first-trimester screening. This prior screening ultimately decreases the prevalence of fetal Down syndrome in the second trimester to less than 85% of what it was in the first-trimester as most fetuses with Down syndrome are now identified early. Current interpretation of the second-trimester Down syndrome markers must be based on the result of the first trimester and combined screening to achieve the most accurate risk estimate of an affected fetus.

Fetal thickened nuchal soft tissues may first appear in the second trimester in Down syndrome

PURPOSE

To describe a series of cases of late-onset fetal nuchal translucency in Down syndrome.

METHOD

In our practice area, most pregnant women usually undergo 3 different sonographic examinations: a fetal nuchal translucency examination in the 1st trimester and 2 detailed surveys of all fetal organs in the early 2nd trimester and in midpregnancy.

RESULT

During the study period (2003-2008), we detected 11 fetuses with new appearance of severe thickened nuchal soft tissues (>or=6 mm) at 14-16 weeks' gestation after a normal nuchal screening in the 1st trimester. All of these fetuses had trisomy 21. Associated structural anomalies were observed in 10/11 of the cases. In addition, there were 12 fetuses with new appearance of thickened nuchal soft tissues (<4 mm); all these fetuses had a normal karyotype and were normal at delivery.

CONCLUSION

Obstetricians should be aware that a nuchal abnormality may first appear only at 14-16 weeks' gestation. Fetal karyotyping is advocated in these cases because of the high probability of Down syndrome.

Use of the genetic sonogram in the United States in 2001 and 2007

OBJECTIVE

The purpose of this study was to determine whether there have been changes in the use of second-trimester genetic sonograms and in the second-trimester sonographic markers used to screen for fetal aneuploidy by maternal-fetal medicine specialists in the United States from 2001 to 2007.

METHODS

A survey was mailed to Society for Maternal-Fetal Medicine members in the United States in April 2007 inquiring about their practice patterns regarding the genetic sonogram. Specific sonographic markers used for risk adjustment as part of the genetic sonogram were also assessed. The responses from 2007 were compared with responses from a similar survey administered in 2001 (Am J Obstet Gynecol 2002; 187:1230-1234) using descriptive statistics, the chi(2) test, and the Wilcoxon rank sum test.

RESULTS

A total of 991 responses were analyzed: 543 of 1638 (32%) in 2001 and 448 of 1756 (26%) in 2007. Significant increases (P < .0001) were noted in the number of specialists who used the genetic sonogram as a screening tool for Down syndrome and for every single sonographic marker used to adjust a woman's risk for having a fetus with Down syndrome during a genetic sonogram, except for choroid plexus cyst, clinodactyly, sandal gap toes, and widened pelvic angle.

CONCLUSIONS

Practitioners in the United States are using an increasing number of second-trimester sonographic markers to help identify aneuploid fetuses. The growing acceptance of sonography to screen for fetal aneuploidy and the recommendation by the American College of Obstetricians and Gynecologists for universal screening suggest that more resources may be necessary to meet the growing demand for second-trimester sonograms.

Expected performance of second trimester maternal serum testing followed by a 'genetic sonogram' in screening of fetal Down syndrome

OBJECTIVE

To assess the efficacy of screening for fetal Down syndrome through the sequential provision of second trimester maternal serum tests and fetal ultrasound (the 'genetic sonogram').

METHODS

Monte Carlo modeling was used to generate typical results for second trimester serum screening. Serum test likelihood ratios were then multiplied by likelihood ratios associated with the provision of a genetic sonogram. The impact of adding the genetic sonogram on the detection rate (DR) and false-positive rate (FPR) were assessed for typical protocols that are currently in use. The effect of expanding the number of women who receive the genetic sonogram, variation in the marker frequencies in the genetic sonogram, and a multivariate Gaussian model that incorporated both serum and ultrasound measurements as continuous variables were also considered.

RESULTS

When the genetic sonogram is offered only to those women who are screen-positive by serum testing, there can be a substantial reduction in the number of women with an indication for amniocentesis but also some loss in detection. The extent of these changes will partially depend on the serum tests and cutoff used. Providing the genetic sonogram to more women can reduce loss in detection without resulting in high amniocentesis rates. As a sequential screening tool, the genetic sonogram can be improved by incorporating markers that have a high frequency in affected pregnancies and by using ultrasound measurements as continuous variables.

CONCLUSION

It should be possible to provide highly effective multistep screening protocols that maximize the benefits of both maternal serum and ultrasound while minimizing the amount of testing offered.

Ultrasonographic findings of fetal aneuploidies in the second trimester--our experiences

OBJECTIVES

The aim of this study was to determine the incidence of ultrasound findings in common fetal chromosomal defects on a relatively large series coming out from one institution. We also tried to evaluate possible clusters of ultrasound signs of major chromosomal defects.

METHODS

Of the 22,150 fetal karyotypings, 514 abnormal karyotypes (2.3%) were diagnosed prenatally between 1990 and 2004. Of them, 374 were further evaluated for abnormal ultrasound signs in this study. These represented the major chromosomal defects of Down syndrome (n = 207), trisomy 18 (n = 70), trisomy 13 (n = 28) and Turner syndrome (n = 69).

RESULTS

The incidences of major structural defects and minor anomalies were evaluated then sonographic signs with the highest incidences were established in each of the major chromosomal defects. In fetuses with trisomy 13, besides cardiac defects, the most frequently seen structural abnormalities were central nervous system anomalies and facial anomalies. In fetuses with trisomy 18 and trisomy 21, cardiac anomalies were the most common structural sonographic features, whereas the most common findings were hygroma colli and fetal hydrops in fetuses with Turner syndrome. As far as minor anomalies are concerned, increased nuchal fold was the most predictive marker of each major aneuploidy. Choroid plexus cysts were more common in trisomy 18, whereas echogenic intracardiac foci were more frequently detected in fetuses with trisomy 13 and trisomy 21.

CONCLUSION

This study may help to select the most predictive components of the genetic sonogram which may assist the counseling of women for the actual risk of the major chromosomal abnormalities.

Genetic sonography after first-trimester Down syndrome screening

OBJECTIVE

Approximately 90% of Down syndrome cases are detected during first-trimester screening. We aimed to determine the potential effectiveness of second-trimester genetic sonography as a sequential screen for Down syndrome.

METHODS

In this simulation study, published statistical parameters for first-trimester free beta-human chorionic gonadotropin, pregnancy-associated plasma protein-A and nuchal translucency thickness, and second-trimester ultrasound markers (nuchal fold, hyperechoic bowel, short humerus, short femur, echogenic intracardiac focus, pyelectasis and major abnormality) were used to model the effectiveness of second-trimester genetic sonography combined with first-trimester screening.

RESULTS

First-trimester combined screening alone resulted in a detection rate of 88.5% with a 4.2% false-positive rate. A follow-up genetic ultrasound examination in which only one sonographic marker was found and previous results were not taken into account would detect an additional 8% of Down syndrome cases for an additional false-positive rate of 13.2%. Using individual marker likelihood ratios to modify the first-trimester risk for screen-negative patients, genetic sonography detected an additional 6.1% of Down syndrome cases for an additional 1.2% false-positive rate, giving a total detection rate of 94.6% and a total false-positive rate of 5.4%. In a contingent protocol, in which genetic sonography would be performed only for patients with a first-trimester risk of between 1/300 and 1/2500, the detection rate was 4.8% and the false-positive rate was 0.7%, giving a total detection rate of 93.3% and a total false-positive rate of 4.9%.

CONCLUSION

Second-trimester genetic sonography, if used properly, can be an effective sequential screen following first-trimester Down syndrome screening. Further studies on the role of the genetic sonogram as a follow-up to first-trimester combined screening are warranted.

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 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.

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.

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.

A Cost-Effectiveness Analysis of Prenatal Screening Strategies for Down Syndrome

OBJECTIVE

To evaluate which Down syndrome screening strategy is the most cost-effective.

METHODS

Using decision-analysis modeling, we compared the cost-effectiveness of 9 screening strategies for Down syndrome: 1) no screening, 2) first-trimester nuchal translucency (NT) only, 3) first-trimester combined NT and serum screen, 4) first-trimester serum only, 5) quadruple screen, 6) integrated screening, 7) sequential screening, 8) integrated serum only, or 9) maternal age. Costs included cost of tests and resources used for raising a child with Down syndrome. One-way and multiway sensitivity analyses were performed for all model variables. The main outcome measures were cost per Down syndrome case detected, rate of delivering a liveborn neonate with Down syndrome, and rate of diagnostic procedure-related pregnancy loss for each strategy.

RESULTS

Sequential screening detected more Down syndrome cases compared with the other strategies, but it had a higher procedure-related loss rate. Integrated serum screening was the most cost-effective strategy. Sensitivity analyses revealed the model to be robust over a wide range of values for the variables. The addition of the cost of genetic sonogram to the second-trimester strategies resulted in first-trimester combined screening becoming the most cost-effective strategy.

CONCLUSION

Within our baseline assumptions, integrated serum screening was the most cost-effective screening strategy for Down syndrome. If the cost of nuchal translucency is less than dollars 57 or when genetic sonogram is included in the second-trimester strategies, first-trimester combined screening became the most cost-effective strategy.

LEVEL OF EVIDENCE

III.

[Role of "subtle" ultrasonographic signs during antenatal screening for trisomy 21 during the second trimester of pregnancy: meta-analysis and CPDPN protocol of the Grenoble University Hospital]

OBJECTIVE

A meta-analysis about subtle ultrasonographic signs in second trimester of pregnancy.

MATERIALS AND METHODS

196 articles dealing with the subject--from 1985 to July 2002--were studied. Data on the 11 reported signs were collected from 92 theoretically and/or statistically valid studies. Then, the studies were selected according to several criteria: isolated characteristic, defined thresholds, calculable sensitivity and specificity. After checking for homogeneity, a likelihood ratio was calculated for some of the signs.

RESULTS

This meta-analysis of the second trimester ultrasonographic signs of Down's syndrome enabled us to estimate the likelihood ratio (LHR) of six signs. At 22 weeks'gestation (WG) these signs are: pyelectasis equal to or greater than 5 mm; nuchal fold thickness equal to or greater than 6 mm; persistence of choroid plexus cysts; shortness of the femur and humerus below the tenth percentile; hyperechogenic bowe; and nasal bone length less than 2.5 mm.

CONCLUSION

These validated ultrasonographic signs are independent of nuchal translucency thickness at 12 WG and of maternal serum biochemistry. This allows to calculate a combinate risk for nuchal translucency, maternal serum biochemistry and second trimester ultrasonographic signs when they are validated.

The mid-trimester genetic sonogram

The genetic sonogram is a composite algorithm combining multiple individual markers to increase Down syndrome risk prediction. Transformation of sonographic information into a standard mathematical format represented an early challenge that has now been surmounted. Using increasingly sophisticated mathematical techniques, individual patient risk can be estimated. High diagnostic accuracy comparable to standard mid-trimester serum algorithms has been reported. Most recently, a few studies have reported the ability to combine serum and biochemical markers to achieve diagnostic accuracy comparable to first-trimester screen. Even fewer studies have reported combinations of ultrasound and maternal urine markers. While it is clear that consistently high sensitivity and specificity for Down syndrome can be achieved, almost all the studies are based on high-risk groups. Studies in low-risk populations have suffered from lack of standardization. The relevance of genetic sonogram in a low-risk population thus remains to be proven. The most significant challenge, however, remains the development of uniform and reproducible sonographic and measurement standards. This is likely to be the most important factor in optimizing the accuracy of the mid-trimester genetic sonogram.

Down syndrome births in the United States from 1989 to 2001

OBJECTIVE

We investigated the observed and expected Down syndrome livebirths in the US from 1989 to 2001.

STUDY DESIGN

Using birth certificate data, we recorded maternal age-specific live births from 1989 to 2001, and stratified them by women 15 to 34 and 35 to 49 years old. We estimated Down syndrome live births from 1989 to 2001, assuming no terminations. We recorded Down syndrome live births by year from 1989 to 2001.

RESULTS

Despite an expected 1.32-fold increase in Down syndrome live birth rates from 1989 to 2001, Down syndrome live births actually declined. In 1989, the rate of Down syndrome cases was 15% lower than expected, decreasing to 51% by 1998. Women 15 to 34 had 45% fewer affected pregnancies in 2001, while women 35 to 49 had 53% fewer in 2001. We estimated that Down syndrome live births decreased from 3962 in 1989 to 3654 in 2001.

CONCLUSION

Down syndrome live births declined in the US despite an expected increase caused by delayed or extended childbearing.

An outcomes analysis of five prenatal screening strategies for trisomy 21 in women younger than 35 years

OBJECTIVE

This study was undertaken to examine the cost-effectiveness and procedural-related losses associated with 5 prenatal screening strategies for fetal aneuploidy in women under 35 years old.

STUDY DESIGN

Five prenatal screening strategies were compared in a decision analysis model: triple screen: maternal age and midtrimester serum alpha-fetoprotein, human chorionic gonadotropin (hCG), and unconjugated estriol; quad screen: triple screen plus serum dimeric inhibin A; first-trimester screen: maternal age, serum pregnancy-associated plasma protein A and free beta-hCG and fetal nuchal translucency at 10 to 14 weeks' gestation; integrated screen: first-trimester screen plus quad screen, but first-trimester results are withheld until the quad screen is completed when a composite result is provided; sequential screen: first-trimester screen plus quad screen, but the first-trimester screen results are provided immediately and prenatal diagnosis offered if positive; later prenatal diagnosis is available if the quad screen is positive. Model estimates were literature derived, and cost estimates also included local sources. The 5 strategies were compared for cost, the numbers of Down syndrome fetuses detected and live births averted, and the number of procedure-related euploid losses. Sensitivity analyses were performed for parameters with imprecise point estimates.

RESULTS

In the baseline analysis, sequential screening was the least expensive strategy ($455 million). It detected the most Down syndrome fetuses (n=1213), averted the most Down syndrome live births (n=678), but led to the highest number of procedure-related euploid losses (n=859). The integrated screen had the fewest euploid losses (n=62) and averted the second most Down syndrome live births (n=520). If fewer than 70% of women diagnosed with fetal Down syndrome elect to abort, the quad screen became the least expensive strategy.

CONCLUSION

Although sequential screening was the most cost-effective prenatal screening strategy for fetal trisomy 21, it had the highest procedure-related euploid loss rate. The patient's perspective on detection versus fetal safety may help define the optimal screening strategy.

Second trimester choroid plexus cysts and trisomy 18

OBJECTIVES

In this study, the aims were to reveal the incidence of isolated choroid plexus cyst in our population, and to discuss the accuracy of distinguishing either an isolated or non-isolated choroid plexus cyst.

METHODS

The study population was consisted of 10594 pregnant women. The patients with choroid plexus cysts were classified into two groups: isolated and non-isolated. Detailed ultrasonographic examination and genetic counseling were performed and triple screening test was ordered. The incidence, sensitivity, specificity, false-positive rate and likelihood ratio of cases with isolated choroid plexus cyst for trisomy 18 were determined.

RESULTS

Choroid plexus cysts were identified in 109 patients (109/10594; 1.02%). In 102 patients isolated choroid plexus cysts, and in seven patients additional fetal anomalies supporting trisomy 18 were detected. Trisomy 18 was detected in four patients, and one of them had isolated choroid plexus cyst. The likelihood ratio in cases of isolated choroid plexus cysts for trisomy 18 was 9.51 (95% confidence interval, 0.2-41).

CONCLUSIONS

According to the study the individual risk for trisomy 18 in isolated choroid plexus cyst should be calculated by using the likelihood ratio. These data allows the physician to express the individual risk of trisomy 18 and permits more accurate genetic counseling.

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.

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.

The use of genetic sonography to reduce the need for amniocentesis in women at high-risk for Down syndrome

Much information has been published regarding the use of second-trimester genetic sonography for the prenatal detection of Down syndrome by examining multiple aneuploidy markers. Among high-risk mothers (advanced maternal age, abnormal triple screen, or both), while many undoubtedly will choose to have invasive testing as a first option, others will instead use the information derived from genetic sonography to obtain an adjusted risk for Down syndrome to guide their decision about genetic amniocentesis. Accordingly, it is imperative that these patients have accurate and detailed counseling regarding their degree of risk reduction when the genetic sonogram is normal. This article reviews the use of second trimester genetic sonography in reducing the need for amniocentesis in the high-risk patient. At our institution, in high-risk patients when the genetic ultrasound is normal, the amniocentesis rate has been only 3%. We have found that genetic sonography is a patient-driven service, and that the information obtained at the time of ultrasound is an important component of the patient's decision of whether or not to proceed with invasive testing.

Nasal bone evaluation in fetuses with Down syndrome during the second and third trimesters of pregnancy

OBJECTIVE

This study examined the use of three-dimensional ultrasonography for evaluating the fetal nasal bone, as a sonographic marker of Down syndrome, during the second and early third trimesters of pregnancy.

METHODS

Forty fetuses, including 20 with trisomy 21, were scanned once by three-dimensional ultrasonography. A midline sagittal view of the facial profile was used to analyze the volume data. Independent examiners reviewed blinded and randomly allocated volume data sets for the nasal bone. Interobserver reliability was evaluated for the sonographic presence or absence of the nasal bone. Logistic regression determined the contribution of this parameter to the presence of Down syndrome.

RESULTS

Both examiners showed substantial agreement in scoring whether the nasal bone was visualized by three-dimensional ultrasonography (P < .001). They identified 40% to 45% of fetuses with abnormalities using the absence of the nasal bone as a sonographic marker. However, a substantial number of fetuses with abnormalities were also found to have a nasal bone present. The nasal bone was visualized in 80% to 90% of fetuses without abnormalities.

CONCLUSIONS

Three-dimensional ultrasonography can be used to evaluate the fetal nasal bone with substantial interobserver agreement during the second and early third trimesters of pregnancy. A nonvisualized nasal bone identified 40% to 45% of fetuses with Down syndrome in this study.

The association between fetal pyelectasis on second trimester ultrasound scan and aneuploidy among 25,586 low risk unselected women

OBJECTIVE

To determine the association of fetal pyelectasis FP found at the time of second trimester detailed ultrasound scan with aneuploidy in an unselected low-risk population.

DESIGN

Retrospective study of ultrasonographic reports, films and hospital notes over an eight-year period from 1991 to 1998.

SETTING

District general hospital obstetric department with 3500 deliveries annually serving a low-risk cosmopolitan population.

MAIN OUTCOME MEASURE

The prevalence of aneuploidy in cases of fetal pyelectasis.

METHODS

The obstetric ultrasound reports and films of 29,591 cases were reviewed to identify those with FP at their detailed anomaly scan between 18 and 24-weeks gestation. The study sample included women whose scan showed the fetal renal pelvis of either kidney to be five millimetres or more in the anteroposterior diameter. Demographic data and other ultrasonographic abnormalities were noted. The genotype and phenotype of the babies were traced from a combination of cytogenetic reports and paediatric notes.

RESULTS

There were 320 cases of FP among the 25,586 low-risk study population available in the studied gestational period (18-24 weeks) giving a prevalence of 1.25 percent. Of these, 301 cases of FP were found in isolation and 19 were found in association with another ultrasonographic marker. None of the 315 cases delivering at the Northwick Park & St. Mark's Hospital had aneuploidy. Pyelectasis was more likely to be bilateral (57%), and more in male fetuses (72%). The mean diameter for the pyelectasis at diagnosis was 6.5 mm (1.4 SD) ranging between 5 and 15 mm. One hundred and thirty seven cases (43%) resulted in spontaneous resolution.

CONCLUSION

The prevalence of FP at the anomaly scan in an unselected low-risk population is not high (1.25%). Our data suggest that the risk of aneuploidy associated with isolated FP in a low-risk, unselected population is so small that it should not be an indication for invasive prenatal karyotyping.

Down syndrome risk estimation after normal genetic sonography

OBJECTIVE

The objective of this study was to determine whether there are any indication-specific variations in risk reduction for fetal Down syndrome after a normal genetic sonogram.

STUDY DESIGN

A second-trimester genetic sonogram was offered to all pregnant women who were at increased risk for fetal Down syndrome (>/=1:274) because of either advanced maternal age (>/=35 years), an abnormal triple screen, or both. Outcome information included the results of genetic amniocentesis (if performed), the results of pediatric assessment, and follow-up after birth. Normal genetic sonography was defined as the absence of all ultrasound aneuploidy markers.

RESULTS

The overall prevalence of fetal Down syndrome in the tested population was 1.41% (53/3,753 pregnancies); however, in the presence of normal genetic sonography, the overall prevalence of fetal Down syndrome was 0.21% (7/3,291 pregnancies). The overall risk reduction for fetal Down syndrome in the presence of normal genetic sonography was 6.64-fold (95% CI, 3.01-14.62); the overall negative likelihood ratio was 0.15 (95% CI, 0.07-0.33). In the presence of normal genetic sonography, the risk for fetal Down syndrome was reduced by 83% in patients with advanced maternal age, 88% in patients with abnormal triple screen, 89% in patients with abnormal triple screen who were <35 years old, and 84% in patients who had both abnormal triple screen and advanced maternal age.

CONCLUSION

There were no significant variations in the risk reduction for fetal Down syndrome in the presence of normal genetic sonography. Regardless of the indication for testing, the likelihood for fetal Down syndrome was reduced by 83% to 89%. This information will be useful in counseling pregnant women who are at high risk for fetal Down syndrome and who prefer to undergo genetic sonography before deciding about genetic amniocentesis.

Second trimester ultrasound screening for chromosomal abnormalities

The use of prenatal ultrasound has proven efficacious for the prenatal diagnosis of chromosomal abnormalities. The first sonographic sign of Down syndrome, the thickened nuchal fold, was first described in 1985. Since that time, multiple sonographically-identified markers have been described as associated with Down syndrome. The genetic sonogram, involving a detailed search for sonographic signs of aneuploidy, can be used to both identify fetuses at high risk for aneuploidy and, when normal, can be used to decrease the risk for aneuploidy for a pregnancy when no sonographic markers are identified. Combining the genetic sonogram with maternal serum screening may be the best method of assessing aneuploidy risk for women who desire such an assessment in the second trimester. Trisomy 18, Trisomy 13, and triploidy are typically associated with sonographically identified abnormalities and have a high prenatal detection rate. The use of the described sonographic signs in low-risk women requires further investigation, however, patients at increased risk for aneuploidy due to advanced maternal age or abnormal serum screening can benefit from a genetic sonogram screening for sonographic signs of aneuploidy to adjust their baseline risk of an affected fetus.

Fetal ear length measurement: a useful predictor of aneuploidy?

OBJECTIVE

To determine the usefulness of short ear length (EL) measurement in the prenatal detection of fetuses with chromosomal abnormalities.

DESIGN

Fetal EL measurements, routine biometry and complete anatomic survey for fetal abnormalities were prospectively performed by antenatal sonography.

SUBJECTS

One thousand eight hundred and forty-eight patients with singleton pregnancies undergoing genetic amniocentesis in the second or third trimester.

METHODS

Complete data for EL, biometry and anatomic survey for major structural abnormalities and minor sonographic markers of chromosomal abnormality were available in 1311 fetuses. Of these, 48 (3.7%) had an abnormal karyotype and 1263 (96.3%) had a normal karyotype. Using an EL measurement of < or = 10th percentile for corresponding gestational age in normal fetuses as abnormal cut-off values, detection rates for chromosomal abnormalities by short EL were determined.

RESULTS

Among the 48 abnormal karyotypes, 34 were considered significant, and 11 of these 34 (32.4%) fetuses had short EL. In 14 cases, the karyotypic abnormality was considered non-significant and fetal EL was normal in all cases. Of the 34 fetuses with significant chromosomal abnormalities, six (17.6%) on antenatal sonography had no detectable abnormal findings, other than short EL. An increased biparietal diameter (BPD)/EL ratio of > or = 4.0 was also noted in fetuses with an abnormal karyotype, but the sensitivity and predictive value of increased BPD/EL ratio alone or increased BPD/EL ratio in combination with short EL was no better than the sensitivity and predictive value of short EL alone. A combination of short EL and abnormal ultrasound, however, gave a much higher positive predictive value (46%) for significant chromosomal abnormalities.

CONCLUSIONS

Our findings suggest that in women at high risk for fetal chromosomal abnormality, a short fetal EL measurement on prenatal ultrasound, either alone or in combination with other sonographically detectable structural abnormalities, may be a useful parameter in predicting fetal aneuploidy.

Fetal iliac angle measurements by three-dimensional sonography

OBJECTIVE

To determine the technical reliability of fetal iliac angle measurements by three-dimensional sonography as a prenatal marker for Down syndrome.

METHODS

Three-dimensional multiplanar views of the fetal pelvis were used to standardize iliac angle measurements from 35 normal second-trimester pregnancies. Measurement reliability for a single examiner and between two different examiners were analyzed by intraclass correlation. Normal iliac angle measurements were compared to those obtained from 16 fetuses with trisomy 21.

RESULTS

The mean axial angle for normal fetuses was 79 +/- 5.5 degrees, which was significantly less than that observed in fetuses with trisomy 21 (87.7 +/- 4.9 degrees ) (P < 0.001). Iliac angles did not correlate with gestational age. Axial angles were reproducible between two examiners who measured the same multiplanar view of the pelvis. Inter- and intraobserver reliability were also acceptable after a standardized multiplanar view was independently obtained by each examiner (intraclass correlation = 0.91 for both). Coronal angles were unreliable because of difficulties with finding a reproducible measurement plane. For a false-positive rate of 5%, an axial angle threshold of 87 degrees correctly identified 56% of fetuses with trisomy 21.

CONCLUSION

Axial iliac angle measurements are reliable by standardized three-dimensional multiplanar views of the pelvis and can be used to identify some fetuses at increased risk for trisomy 21.

Obstetric ultrasonographic findings and fetal chromosomal abnormalities: refining the association

OBJECTIVE

In an attempt to refine the role of ultrasonography in screening and identifying fetuses at risk for chromosomal abnormalities, a retrospective review of patients undergoing genetic amniocentesis was undertaken.

STUDY DESIGN

Computer databases from the perinatal biology laboratory and cytogenetics laboratory of our institution were correlated to compare the results of the fetus' ultrasonographic examination with the cytogenetic results from amniocentesis. Univariate and multivariate analysis were used to determine the best correlations between ultrasonographic findings and chromosomal abnormalities (study 1). The results were used to construct regression analysis formulas and a Neural Network program to predict the presence or absence of chromosomal abnormalities in a second set of patients (study 2) undergoing genetic amniocentesis.

RESULTS

One hundred twenty-five chromosomal abnormalities were found in 3775 fetuses in study 1 (3.3%). Multivariate analysis showed significant correlations between anomalies of the central nervous system, heart, face and neck, and extremities and increased nuchal fold, increased bowel echogenicity, abnormal biparietal diameter-to-femur ratio, and the presence of chromosomal abnormalities. Regression equations and a Neural Network program successfully predicted the presence or absence of fetal chromosomal abnormalities in a second set of 901 at-risk fetuses.

CONCLUSION

A normal ultrasonographic examination result in patients who are at increased risk for fetal chromosomal abnormalities reduces the risk 2- to 3-fold, whereas the presence of any major ultrasonographic abnormality or certain minor abnormalities significantly increases the risk. The application of these results to low-risk patients is still premature.

Ultrasonographic ear length measurement in normal second- and third-trimester fetuses

OBJECTIVE

We sought to develop a nomogram for fetal ear length measurements from a large population of healthy second- and third-trimester fetuses and to investigate the correlation of fetal ear length with other standard fetal biometry measurements, as follows: biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length.

STUDY DESIGN

Ear length measurement was obtained prospectively in 4240 singleton fetuses between 15 and 40 weeks' gestational age. Either complete data for normal karyotype on amniocentesis or normal infant examination at birth or both were available in 2583 cases. These constituted the final study population.

RESULTS

A nomogram was developed by linearly regressing ear length on gestational age (Ear length [in millimeters] = 1.076 x Gestational age [in weeks] - 7. 308). There was a high correlation between ear length and gestational age (r = 0.96; P =.0001).

CONCLUSION

The results of this study provide normative data on growth of fetal ear length from 15 to 40 weeks' gestation. Good correlation was also observed between ear length and other fetal biometric measurements (biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length).

Combined ultrasound biometry, serum markers and age for Down syndrome risk estimation

OBJECTIVE

To compare Down syndrome screening efficiency of the standard serum triple analyte screen to that of a four-component screen consisting of ultrasound biometry and serum markers in the second trimester.

METHODS

The Down syndrome screening efficiency of the triple screen, i.e. alpha-fetoprotein (AFP), unconjugated estriol (E3), hCG and maternal age, was compared with the four-marker algorithm, i.e. humerus length, nuchal thickness, AFP and hCG plus maternal age. A quadrivariate Gaussian algorithm was used to calculate individual Down syndrome odds. Receiver operating characteristic (ROC) curves plotting sensitivity against false-positive rate were constructed for each algorithm and the areas under the curves were compared to determine which was superior. Sensitivity and false-positive rates at different Down syndrome risk thresholds were also compared.

RESULTS

There were 46 cases of Down syndrome (1.9%) with 2391 normal singleton pregnancies in a referral population in which triple screen, fetal biometry and karyotype had been done. The gestational age range for the study was 14-24 completed weeks. The median maternal age for the study group was 35.0 years (14.0-46.0 years). The areas (SE) under the ROC curves were 0.75(0.04) and 0.93(0.02) for the standard triple and the four-marker screen, respectively (P < 0.001). At a 10% false-positive rate, detection was 45.7% for the triple and 80.4% for the four-marker screen.

CONCLUSIONS

A new algorithm combining humerus length and nuchal thickness measurement with serum AFP, hCG and maternal age substantially improved Down syndrome screening efficiency compared with the traditional triple screen. The model appears promising and should be evaluated in an independent data set.