Second-trimester ultrasound markers for detection of trisomy 21: which markers are best?

Prenatal diagnosis of Cri-du-Chat syndrome with concomitant distal trisomy 10q syndrome in one fetus with ultrasound anomalies

OBJECTIVE

The aim of this work was to characterize the genetic abnormalities and prenatal diagnosis indications in one fetus with Cri-du-Chat syndrome with codependent 10q24.2-q26.3 duplication in prenatal screening.

MATERIALS AND METHODS

A 31-year-old woman had a second trimester serum screening that indicated the fetus was at low risk. During this pregnancy, the woman underwent amniocentesis at 18⁺⁴ weeks' gestation because of adverse fertility history and nuchal fold thickening. Cytogenetic analysis and next-generation sequencing analysis were simultaneously performed to provide genetic analysis of fetal amniotic fluid. According to abnormal results, parental chromosome karyotype of peripheral blood was performed to analysis.

RESULTS

CNV-seq detected a 14.00 Mb deletion at 5p15.33-p15.2 and a 34.06 Mb duplication at 10q24.2-q26.3 in the fetus. Cytogenetic analysis of the fetus revealed a karyotype of 46, XY, der(5) t(5;10) (p15.2;q26.3). The karyotype of pregnant women was 46,XX,t(5;10) (p15.2;q24.2). The pregnancy was subsequently terminated after sufficient informed consent.

CONCLUSION

This is the first study that reports prenatal diagnosis of a Cri-du-Chat syndrome with concomitant 10 q24.2-q26.3 duplication. Adverse pregnancy history has to be as an important indicator for prenatal diagnosis, and the genetic factors of abnormal pregnancy should be identified before next pregnancy. Nuchal fold thickening is closely related to fetal abnormalities. Combined with ultrasonography, the use of CNV-seq will improve the diagnosis of submicroscopic chromosomal aberrations in fetuses with congenital anomalies.

Prenatal diagnosis of congenital upper limb differences: a current concept review

Congenital upper limb differences are frequently associated with complex syndromes. Ultrasonography is considered as the first-line diagnostic modality, and fetal MRI can be useful to further evaluate ill-defined areas. Genetic and non-invasive prenatal testing help to identify the underlying genetic disorder. The diagnostic assessment is a multidisciplinary task that should involve early prenatal consultations with specialists involved in case management and treatment planning. Obstetricians, geneticists, radiologists, psychologists and dedicated surgeons are needed to provide good parental education, prenatal and postnatal care, and successful outcomes. The purpose of this review is to provide an overview of the clinicopathologic background, current diagnostic and imaging procedures in affected fetuses.

Influence of second-trimester ultrasound markers for Down syndrome in pregnant women of advanced maternal age

The objective of the present study was to evaluate the influence of second-trimester ultrasound markers on the incidence of Down syndrome among pregnant women of advanced maternal age. This was a retrospective cohort study on 889 singleton pregnancies between the 14th and 30th weeks, with maternal age ≥ 35 years, which would undergo genetic amniocentesis. The second-trimester ultrasound assessed the following markers: increased nuchal fold thickness, cardiac hyperechogenic focus, mild ventriculomegaly, choroid plexus cysts, uni- or bilateral renal pyelectasis, intestinal hyperechogenicity, single umbilical artery, short femur and humerus length, hand/foot alterations, structural fetal malformation, and congenital heart disease. To investigate differences between the groups with and without markers, nonparametric tests consisting of the chi-square test or Fisher's exact test were used. Moreover, odds ratios with their respective 95% confidence intervals were calculated. Out of the 889 pregnant women, 131 (17.3%) presented markers and 758 (82.7%) did not present markers on the second-trimester ultrasound. Increased nuchal fold (P < 0.001) and structural malformation (P < 0.001) were the markers most associated with Down syndrome. The presence of one marker increased the relative risk 10.5-fold, while the presence of two or more markers increased the risk 13.5-fold. The presence of markers on the second-trimester ultrasound, especially thickened nuchal fold and structural malformation, increased the risk of Down syndrome among pregnant women with advanced maternal age.

"I'm not a saint": burden assessment as an unrecognized factor in prenatal decision making

Prenatal testing is widely utilized, yet few studies have explored decision-making processes about diagnosis from the pregnant woman's standpoint. This qualitative, exploratory study reveals a factor not accounted for in prior research geared toward associations between demographic categories and decisions. The 30 women in this study demonstrated a three-part decisional trajectory that included an effort to collect information about the challenges a potential child with their particular diagnosis might experience. They then assessed their social context, familial supports, and resilience as a couple. A final yet crucial step was an assessment of the woman's own capacity to provide this level of care within her unique context. Few genetics teams have a member with biopsychosocial expertise and time who can help the woman/couple reflect on the situated context of the decision and its impact. Better care strategies to support women and couples through this experience are warranted.

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.

Sonographic visualization of the middle phalanx of the fetal fifth digit between 13 and 17 weeks of gestation

OBJECTIVE

To assess in utero visualization of the middle phalanx of the fifth digit (MPFD) between 13 and 17 weeks of gestation.

METHODS

This was a prospective cross-sectional study in which women attending for fetal sonographic examination between 13 + 0 and 17 + 6 weeks of gestation were evaluated for the presence of the middle phalanx of the fifth digit (MPFD). A total of 682 fetuses with normal findings on first-trimester anatomical examination were recruited. Using transvaginal multifrequency 4-8 and 5-9 MHz probes, the fifth finger was examined in both axial and lateral views until optimal visualization of the MPFD was achieved.

RESULTS

The MPFD was visualized in 14.3% (2/14) of cases at 13 weeks, 70.3% (154/219) at 14 weeks, 82.2% (240/292) at 15 weeks, 97.4% (111/114) at 16 weeks and 100% (43/43) at 17 weeks of gestation.

CONCLUSIONS

Ultrasound visualization of the MPFD gradually increases during the 13- to 17-week period. This emphasizes the limited role of non-ossification of the MPFD as a sonographic marker of Down syndrome before 17 weeks of gestation.

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.

Screening for aneuploidy in first and second trimesters: is there an optimal paradigm?

PURPOSE OF REVIEW

This review serves to explore the recent literature regarding aneuploidy screening in both first and second trimesters. We aim to construct a comparative analysis of a range of proposed strategies for screening for trisomy 21.

RECENT FINDINGS

First trimester combined screening (sonographic nuchal translucency combined with serum markers pregnancy-associated plasma protein A and the free beta subunit of human chorionic gonadotrophin) has superseded second trimester serum screening (alpha-fetoprotein, total human chorionic gonadotrophin, unconjugated estriol with or without inhibin-A) as a screening paradigm for the detection of trisomy 21. This move is attributed to the recognition of superior detection rates, lower false-positive rates and earlier results associated with the former strategy. Septated cystic hygroma has been recognized as a distinct entity which confers a high risk of aneuploidy and structural malformations. Further advances in screening performance are achievable by combining the results of first and second-trimester screens in a sequential manner, with much interest generated by programs that only include second-trimester testing contingent upon first-trimester results.

SUMMARY

Screening strategies for aneuploidy continue to evolve, with the most recent evidence favouring a contingent sequential approach.

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.

Ultrasound diagnostic schema for the determination of increased risk for chromosomal fetal aneuploidies in the first half of pregnancy

The aim of the study was to develop an early ultrasound diagnostic schema for the determination of increased risk for fetal chromosomal aneuploidies. The study was conducted on a population of 1318 pregnant women divided into 2 groups: 1255 women with the normal course of pregnancy and 63 women with diagnosed fetal abnormalities. There were 34 cases of chromosomal abnormalities (trisomy 21, 18, 13; triploidy; unbalanced inversion 9; deletion 16) and 29 cases of structural malformations. The estimation of the range of normal values was performed for the nuchal translucency (NT) measurement between 11 and 13 weeks and the nasal bone length (NB) measurement between 12 and 20 week. The results obtained in the collective set of normal pregnancies constituted the basis for the calculation of the range of normal values. The measurements of NB and NT showed a linear value increase with the pregnancy course. The following test characteristics (correlation to CRL) were recorded: NB - sensitivity 60%, specificity 98%, positive predictive value (PPV+) 43%, negative predictive value (NPV-) 98.9%. For the assumption that the test outcome means the presence or absence of the nasal bone in the ultrasound scan the sensitivity was 40%, but specificity 100%; NT - sensitivity 63.6%, specificity 98.2%, PPV+ 38.9%, NPV - 98.2%; NT + NB - presents similar characteristic to the NB or NT alone - sensitivity 55.6%, specificity 98.6%, PPV+ 50%, NPV - 98.9%. The following test characteristics for chromosomal aberration markers (correlation to BPD) were observed: NB - sensitivity 68.4%, specificity 97.4%, PPV+ 56.5%, NPV - 98.4%; NT - sensitivity 73.9%, specificity 97.9%, PPV+ 54.8%, NPV- 99.2%; NT + NB - sensitivity 94.7%, specificity 98.9%, PPV+ 90%, NPV - 99.7%, respectively. The "genetic sonogram" protocol for the structural defect detection was analysed: sensitivity was 80%, specificity 100%, PPV+ 100%, NPV - 99.7%. It is concluded that the new biometric parameter--nasal bone length (NB) and the corrected one--nuchal translucency thickness (NT) are useful markers for fetal abnormalities, especially for chromosomal aberrations. High predictive values of the diagnostic schema for the detection of aneuploidies and structural defects indicate that its application in correlation with the biparietal diameter (BPD) is highly recommended. The proposed schema is an effective algorithm for prenatal diagnostics characterised by high prognostic values. The possible introduction of the schema could result in a decrease of the invasive procedure rates, which could minimise the rate of miscarriages as a complication of amniocenteses.

First-trimester maternal serum levels of placental hormones are independent predictors of second-trimester fetal growth parameters

OBJECTIVE

To determine whether first-trimester maternal serum levels of pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (fbeta-hCG) are independent predictors of second-trimester fetal growth parameters.

METHODS

This was a cohort study over a 1-year period involving 594 Chinese women who underwent both first-trimester combined screening for Down syndrome and a routine second-trimester ultrasound examination. Maternal PAPP-A and fbeta-hCG levels (expressed in log(10) of multiples of median (MoM)), crown-rump length (CRL) (expressed in standardized Z-score (Z-CRL)), and maternal height and weight, were correlated with the Z-score of biparietal diameter (Z-BPD), femur length (Z-FL) and abdominal circumference (Z-AC) measured in the second trimester, using the Pearson test, followed by multiple regression analysis.

RESULTS

Z-BPD, Z-FL and Z-AC were positively correlated with log(10) PAPP-A MoM, CRL and maternal height (all P < 0.05), while log(10) fbeta-hCG MoM was negatively correlated with Z-AC (P < 0.05). After controlling for the effects of CRL, maternal height and weight, log(10) PAPP-A MoM was found to be an independent positive predictor of Z-FL (r = 0.797, P < 0.001) and Z-AC (r = 0.305, P = 0.049), and log(10) fbeta-hCG MoM was an independent negative predictor of Z-FL (r = -0.381, P = 0.023) and Z-AC (r = -0.418, P = 0.002). Neither hormonal level was related to Z-BPD.

CONCLUSIONS

First-trimester PAPP-A and fbeta-hCG are independent factors that influence subsequent fetal growth. PAPP-A level is positively correlated with FL and AC in the second trimester, while fbeta-hCG level is negatively correlated with them. However, BPD is not affected by either of the hormones.

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.

Isolated fetal pyelectasis and chromosomal abnormalities

OBJECTIVE

The primary objective of this study was to determine if isolated pyelectasis is a risk factor for trisomy 21.

STUDY DESIGN

Twelve thousand, six hundred and seventy-two unselected singleton fetuses were examined by prenatal ultrasound during the second trimester at a single institution. The sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio of pyelectasis (either isolated or in association with other soft markers/structural anomalies) to detect trisomy 21 were calculated.

RESULTS

Pyelectasis (anteroposterior pelvic diameter >/=4 mm) was detected in 2.9% (366/12,672) of the fetuses. Among these, 83.3% (305/366) were isolated, and 16.7% (61/366) were associated with other markers/structural anomalies. The prevalence of trisomy 21 was 0.087% (11/12,672) and, among these fetuses, 2 (18.1%) had pyelectasis, 1 isolated, and 1 associated with other markers/structural anomalies. The presence of isolated pyelectasis had 9.09% sensitivity, 97.6% specificity, 0.33% positive predictive value, and 99.9% negative predictive value to detect fetuses with trisomy 21. The likelihood ratio of trisomy 21 in this group of fetuses was 3.79 (95% CI 0.582-24.616). Among fetuses with pyelectasis and other associated markers/structural anomalies, the sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio for trisomy 21 were 9.09%, 99.5%, 1.64%, 99.9%, and 19.2 (95% CI 2.91-126.44).

CONCLUSION

In the absence of other findings, isolated pyelectasis is not a justification for the performance of an amniocentesis.

[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.

First- and midtrimester Down syndrome screening and detection

Overall, Down syndrome detection capabilities have improved remarkably over the last 2 decades. Widely practiced first-trimester screening and less extensively elevated midtrimester urine screening promise even greater accuracy than was available a decade ago. Recently, the combination of first- and second-trimester screening has been reported to enhance discrimination of the Down syndrome fetus from normal cases. Although the advances are welcome, they present the significant prospect of multiple competitive algorithms with the risk of confusing patients, practitioners, and health care planners. The need for reasonable consensus has never been more pressing.

Correlation of second-trimester sonographic and biochemical markers

OBJECTIVES

To investigate correlations between sonographic soft markers and biochemical markers (human chorionic gonadotrophin, alpha-fetoprotein, and estriol) for Down syndrome in the second trimester of pregnancy.

METHODS

A total of 2183 women with apparently normal singleton fetuses who underwent second-trimester sonography (14-22 weeks) and maternal serum biochemical testing (triple test) were identified. Seven sonographic markers were recorded: nuchal fold thickness, humerus length, femur length, renal pyelectasis, hyperechoic bowel, echogenic intracardiac focus, and choroid plexus cysts.

RESULTS

Weak negative but statistically significant correlations were observed between human chorionic gonadotropin (multiples of the median) and both femur length (multiples of the median; Spearman p = -0.073; P < .01) and humerus length (multiples of the median; Spearman p = -0.083; P < .01). No other correlations significant at the 1% level were observed between femur length (multiples of the median) or humerus length (multiples of the median) and the biochemical markers. There were no significant correlations between nuchal fold thickness and any of the 3 biochemical markers. At the 5% (P < .05) level, the median human chorionic gonadotropin level (multiples of the median) was lower when an echogenic intracardiac focus was detected. Hyperechoic bowel also tended to be associated with higher median human chorionic gonadotropin (multiples of the median) and alpha-fetoprotein (multiples of the median) levels (P < .05).

CONCLUSIONS

We found that sonographic and biochemical markers for trisomy 21 are largely independent in unaffected pregnancies. For accurate risk estimation, correlations in both affected and unaffected pregnancies need to be considered. No or minimal correlation between sonographic markers and serum screening tests indicates that they can be used as independent modifiers of the maternal age-specific risk for Down syndrome.

Screening for aneuploidy: the genetic sonogram

Over the past 10 years, the use of ultrasound in aneuploidy risk estimation has improved the way obstetrics is practiced. It allows patients to obtain more personalized risk assessment and has allowed many women a reasonable alternative to invasive testing. The addition of soft markers to the sonographic screening for aneuploidy has been extremely beneficial, especially when considered in combination with other ultrasound findings. The best estimate of risk seems to be achieved through the combined use of ultrasound, maternal serum screening, and maternal age. The literature supports the use of soft markers only when applied to the high-risk population, where the prevalence of aneuploidy is increased. If this information is applied to the low-risk populations, especially in isolation, the lower prevalence of aneuploidy makes the positive predictive value too low to be of any value in counseling patients. As with many screening tests it occasionally misses the diagnosis, and every patient needs to understand this potential shortcoming. It is a personal decision regarding their willingness to accept the risk of a missed diagnosis versus the risk of fetal loss from an invasive procedure. Although it is far from perfect, in the right hands and with appropriate counseling ultrasound is an excellent tool. This is such an important decision for women and their families, and it is worth the time it takes to explain the benefits and limitations of this test.

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.

Prenatal diagnosis for detection of aneuploidy: the options

The value of all noninvasive prenatal tests must be viewed with the perspective of the consequences of invasive testing. Regarding second trimester noninvasive testing, biochemical screening is more accurate in establishing risk than maternal age alone. One or more major ultrasound abnormalities, nuchal thickening, or a shortened humerus should raise concern for Down syndrome regardless of the patient's a priori risk based on age or biochemical markers. Isolated minor ultrasound markers should not be used in calculating risk in low-risk patients regarding Down syndrome unless the biochemical profile already places the patient at risk or in a borderline risk zone. If the ultrasound finding is hyperechoic bowel, problems other than aneuploidy may be the cause, including cystic fibrosis, infection, or hemorrhage, and these problems must be considered if hyperechoic bowel is an isolated finding. Improved risk adjustment seems to be applicable to a priori high-risk patients with completely normal sonograms. Genetic sonograms with specific risk adjustment schemata may be used to adjust a priori risk (either maternal age or biochemical screening results) at centers in which this has proven to be accurate, but whether this is statistically sound remains to be determined. The goal of second trimester ultrasound screening is to identify at-risk fetuses better and offer invasive testing to a more select group of patients. As the value of first trimester screening becomes more evident and practical, and if the risk of chorionic villus sampling becomes an acceptable norm, the patient population that reaches the second trimester of pregnancy will be select. Therefore, we can anticipate that second trimester screening and invasive testing may be needed only in a minority of cases, and the practice standards of prenatal testing and sonography (including minor ultrasound markers) will change entirely.

Combined serum and ultrasound screening for detection of fetal aneuploidy

Experience gathered over the last decade from high-risk centers provide strong evidence that mid-trimester sonographic markers are sensitive for Down syndrome prediction. More recent data indicate that combining mid trimester sonography with traditional serum markers significantly improves diagnostic accuracy over either group of markers by themselves.

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.

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.

Nuchal index: a gestational age independent ultrasound marker for the detection of Down syndrome

OBJECTIVES

To determine if the ultrasound marker Nuchal Index (NIx) is gestational age independent, and to determine its specificity and sensitivity for Down syndrome (DS) identification.

METHODS

Prospective cohort. A prospective database of fetal biometry and soft markers of aneuploidy was searched for fetuses with the following criteria: confirmed gestational age, at least two measurements of nuchal thickness and biparietal diameter, no major detectable fetal anomalies, and either normal karyotype or normal postnatal exam. Nuchal Index (NIx) was defined as 100x (mean nuchal thickness [mm])/(mean Biparietal Diameter [mm]). This cohort was divided into two groups according to the last digit of their hospital unit number. Initial analysis was carried out in the first group (analysis group), with the second group (normal) used to test the results. A prospective cohort of pre- and postnatally diagnosed DS fetuses with at least two measurements of nuchal thickness and biparietal diameter constituted the abnormal study group (abnormal) and was used to determine the sensitivity of the index. P value <0.05 was considered significant.

RESULTS

Eight hundred and seventy-five fetuses constituted the control group with 455 in the analysis group and 420 in the normal group. In the analysis group, Pearson coefficient and ANOVA confirm that NIx was independent of gestational age between 14 + 0 and 22 + 6 weeks of gestation. For the analysis group, mean NIx was 7.72, (SD = 2.05) and a threshold value of 11.0 yielded a specificity of 94%. Fifty-two DS fetuses made up the abnormal group. Mean NIx in this group was 17.9 (SD = 13.9), which was highly significant (P < 0.00001) compared to the analysis group. Using an NIx threshold of 11.0, sensitivity for any DS was 61.5% (32/52) and specificity (normal group) was 96% (402/420) (False positive rate = 4%). If DS fetuses with effusions, hydrops, cystic hygromas or central nervous system (CNS) defects are excluded, the sensitivity for an NIx of 11.0 was 50.0% (20/40).

CONCLUSIONS

Nuchal Index (NIx) can be assumed to be constant between 14 + 0 and 22 + 6. Using a threshold of 11.0, the sensitivity for any Down syndrome (DS) fetus was 62% (32/52) with a specificity of 96% (False positive rate = 4%). Even when obvious fetal conditions that can cause an increase in NIx are excluded, the sensitivity remains acceptable at 50%. NIx appears to be a useful, gestational age independent ultrasound marker for Down syndrome.

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.

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.

Value of humerus length shortening for prenatal detection of Down syndrome in a Thai population

OBJECTIVE

To assess the value of humerus length shortening for prenatal detection of Down syndrome in a Thai population.

METHODS

A prospective study was performed on 3053 women undergoing second-trimester amniocentesis, between 16 and 24 weeks gestation, for the indications of advanced maternal age and a past history of chromosomal abnormality. Biparietal diameter (BPD) and humerus length measurements were obtained before the procedures. Regression equations relating BPD to humerus length were used to calculate observed humerus length/expected humerus length ratio in chromosomally normal and Down syndrome fetuses. Sensitivity, specificity, false-positive rate and likelihood ratio of a positive test result at various observed humerus length/expected humerus length ratios for detection of Down syndrome were calculated. A receiver-operator characteristic curve was used to determine the threshold screening ratio.

RESULTS

There were 3003 chromosomally normal pregnancies and 24 fetuses with Down syndrome. The relationship between humerus length and BPD was: expected humerus length = 0.7403BPD - 5.1057, R2= 0.77, P < 0.001. Humerus length in Down syndrome fetuses was significantly shorter than in normal fetuses (P < 0.001). A ratio of 0.91 for observed humerus length/expected humerus length yielded a sensitivity of 41.7%, specificity of 88.3%, a false-positive rate of 11.7% and likelihood ratio of a positive test result of 3.63 (95% confidence interval 2.24-5.88) for detection of Down syndrome.

CONCLUSIONS

Humerus length shortening in the second trimester appears to be a useful adjunctive screening parameter for fetal Down syndrome in a Thai population.

A negative second trimester triple test and absence of specific ultrasonographic markers may decrease the need for genetic amniocentesis in advanced maternal age by 60%

OBJECTIVE

A study was conducted to evaluate the sensitivity of combining a second trimester triple test and targeted ultrasound in order to detect Down syndrome in women undergoing amniocentesis over 35 years of age.

METHODS

Women over 35 years of age underwent a triple test and an ultrasound examination for chromosomal markers immediately prior to genetic amniocentesis.

RESULTS

One thousand and six women were examined. Four hundred and thirty seven were triple test-positive and in 195 cases ultrasonographic abnormalities were observed. Thirteen had Down syndrome and eight had other chromosomal abnormalities. All women with Down syndrome babies were triple test-positive and seven also had ultrasonographic markers. Three of eight women who had babies with chromosomal aberrations other then Down syndrome were also triple test-positive.

CONCLUSIONS

The use of the triple test as a screening tool in our population would reduce the number of amniocenteses by 60%, while no cases of Down syndrome would be missed. Ultrasonographic markers have added little to this population. Three non-Down syndrome chromosomal abnormalities and two Down syndrome mosaic cases would be missed by this approach.

DOPPLERVELOCIMETRIA DO DUTO VENOSO NO CÁLCULO DE RISCO PARA SÍNDROME DE DOWN NO PRIMEIRO TRIMESTRE DA GRAVIDEZ

OBJETIVO: Investigar a validade da Dopplervelocimetria do duto venoso em detectar a síndrome de Down entre 10 e 14 semanas de gestação e propor novo cálculo de risco. PACIENTES E MÉTODOS: Foram estudados 491 fetos, consecutivamente. Em 132 casos realizou-se estudo citogenético no material obtido por biópsia de vilosidade coriônica e em 359 o resultado baseou-se no fenótipo do recém-nascido. Em todos os fetos realizaram-se, além da ultra-sonografia de rotina, a medida da translucência nucal e a Dopplervelocimetria do duto venoso. Na análise estatística foram utilizados o teste paramétrico T de "student", a análise de variância e a regressão linear. Posteriormente, calcularam-se: sensibilidade, especificidade, valores preditivos positivo e negativo, probabilidade de falso-positivo e razões de probabilidades. RESULTADOS: Ocorreram 21 casos de trissomia do cromossomo 21. Desses casos, o fluxo no duto venoso durante a contração atrial foi ausente em três casos e reverso em 17 - sensibilidade de 95,2%. No grupo de fetos normais (470 casos), oito avaliações mostraram alterações do Doppler do duto venoso (especificidade de 98,2%, valores preditivos positivo e negativo de 71,4% e 99,8%, respectivamente, e razões de probabilidades positiva e negativa de 56 e 0,1, respectivamente). CONCLUSÕES: Nossos resultados preliminares sugerem que a presença de síndrome de Down pode ser fortemente suspeitada se houver fluxo reverso ou ausente no duto venoso. Especulamos a possibilidade de cálculo de novo risco para trissomia do 21 com base no Doppler do duto venoso. Utilizando o programa de risco da Fetal Medicine Foundation como risco basal, teríamos um fator multiplicador de aproximadamente 0,1 (razão de probabilidade negativa), caso duto normal, ou de 50 (razão de probabilidade positiva), caso duto reverso ou ausente, e assim, teremos novo risco corrigido.

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.

Evaluation of fetal femur length to detect Down syndrome in a Thai population

OBJECTIVE

To assess the value of femur length shortening for prenatal detection of Down syndrome in a Thai population.

METHOD

A prospective study was performed by experienced perinatologists on 3137 women undergoing second-trimester amniocentesis, between 16 and 24 weeks of gestation, for the indications of advanced maternal age and past history of chromosomal abnormality. Biparietal diameter and femur length measurements were obtained before the procedures. Regression equations relating biparietal diameter to femur length were used to calculate observed femur length/expected femur length ratio in the chromosomally normal and Down syndrome fetuses. Sensitivity, specificity, false-positive rate and likelihood ratio of a positive test result at various observed femur length/expected femur length ratios for detection of Down syndrome were calculated. A receiver-operator characteristic curve was used to determine threshold screening ratio.

RESULTS

There were 3084 chromosomally normal pregnancies, 26 fetuses with Down syndrome (1:118), and 27 other chromosomal abnormalities. The relationship between femur length and biparietal diameter (BPD) was: expected femur length=-7.631+0.814 BPD, R(2)=0.78, P<0.001). Femur length in Down syndrome fetuses was significantly shorter than in normal fetuses (P<0.001). A ratio of 0.91 for observed femur length/expected femur length yielded a sensitivity of 42.3%, specificity of 86.2%, false positive rate of 13.8% and likelihood ratio of a positive test result of 3.07 (95% CI 1.94-4.84) for detection of Down syndrome.

CONCLUSIONS

In this study, femur length shortening in the second trimester appears to be a useful screening parameter for fetal Down syndrome in a Thai population.

Sonographic markers of fetal aneuploidy

A variety of ultrasound findings can be identified in fetuses with fetal aneuploidy. Typical findings vary with both the chromosome abnormality and gestational age at time of the ultrasound examination. Increased NT is the primary marker during the first trimester, whereas a variety of markers may be seen during the second trimester. The presence of ultrasound markers increases the risk for fetal aneuploidy, whereas a normal ultrasound reduces the risk. Optimal risk assessment includes consideration of other risk factors including maternal age, family history, and biochemical markers. It is expected that combined risks, incorporating ultrasound findings and biochemistry, will be available in the near future. How first-trimester screening is integrated with second-trimester screening remains to be determined.

Trisomy 21: 91% detection rate using second-trimester ultrasound markers

OBJECTIVES

To examine cardiovascular and non-cardiovascular prenatal ultrasound markers and determine which markers physicians of varying skill levels could use to identify fetuses with trisomy 21.

METHODS

Eighty second-trimester fetuses with trisomy 21 and 2000 controls underwent real-time plus color Doppler examination of cardiovascular and non-cardiovascular systems followed by amniocentesis. Non-cardiac markers were central nervous system malformations (CNS); choroid plexus cysts (CPC); abnormal nuchal skin fold (NSF); hyperechoic bowel (HB); and pyelectasis (PY). Cardiac markers consisted of ventricular septal defect, right-to-left chamber disproportion (RL); tricuspid regurgitation; mitral regurgitation (MR); pericardial effusion; and outflow tract abnormalities (OFT). Multinomial logistic regression was used to identify interactivity between the markers. Logistic regression was utilized to identify which combinations of markers significantly contributed to the identification of fetuses with trisomy 21 and to compute the likelihood ratio.

RESULTS

All but three markers (CPC, MR, OFT) contributed significantly to the identification of 91% of fetuses with trisomy 21 with a false-positive rate of 14%. When only non-cardiovascular markers were examined, all but CPC contributed to the identification of 60% of fetuses with trisomy 21 with a false-positive rate of 5.9%. Combining right-to-left chamber disproportion with CNS, NSF, HB and PY identified 75% of fetuses with trisomy 21 with a false-positive rate of 6.4%. All markers were independent predictors of trisomy 21 except RL and NSF.

CONCLUSION

Ultrasound can detect between 60 and 91% of fetuses with trisomy 21 depending upon which markers are selected for evaluation.

Fetal sonographic findings: analysis of the most frequent patterns and their specificity of association

A major goal of obstetric sonography is the detection of patterns of anomalies in order to make a diagnosis, or to determine which pregnant women should be offered invasive testing. Previous studies have analyzed patterns from the perspective of a specific anomaly and its associations, e.g., increased nuchal translucency measurement and structural heart disease. In this study we applied the technique of cluster analysis to a population data set that consisted of fetuses with at least two sonographically detectable anomalies. The specificity of association of the most frequent patterns found in our population was evaluated by means of the ratio of the observed number of fetuses with the findings (O) over the expected number of such fetuses (E). The observation that different patterns aggregate in a relatively small number of clusters was then evaluated by means of cluster analysis for binary data. Results show that several patterns can be considered in nonrandom associations, based on the O/E ratio. Most of these patterns are well known to clinicians but validate this new approach. As cluster analysis is applied to antenatal sonographic data sets, new patterns of associations of anomalies may be detected.

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.

Ultrasound screening for fetal chromosome anomalies

Ultrasound evidence for aneuploidy may be found in almost every organ of the fetus and can be used to modify the risk of aneuploidy. The diagnosis of these minor anomalies on second-trimester ultrasonography will increase the risk of an abnormal karyotype whereas the absence of these findings may reduce this danger. The most specific and most ominous isolated markers for fetal aneuploidy are nuchal findings (edema or cysts), indicating the need to obtain a fetal karyotype in all cases irrespective of maternal age or results of biochemical serum screening. Hyperechoic fetal bowel is apparently also a strong indicator of fetal aneuploidy. Other isolated sonographic markers may increase the risk of an abnormal karyotype three- to ninefold. Most sonographic markers for aneuploidy specify an increased risk for Down syndrome, but choroid plexus cysts are apparently more specific for trisomy 18. Along with other screening methods, ultrasound screening for fetal aneuploidy should be used routinely to identify additional pregnancies at need for evaluation of fetal karyotype.

Critical appraisal of the use of nuchal fold thickness measurements for the prediction of Down syndrome

OBJECTIVE

Nuchal fold thickness is the best ultrasonographic predictor of fetal trisomy 21. However, the risk assigned on the basis of the commonly used threshold of nuchal fold thickness >/=6 mm does not take into consideration the significant associations between nuchal fold thickness and gestational age and between maternal age and Down syndrome. We propose a new method of calculating Down syndrome probability that takes into account both gestational age at examination and previously assessed probability of Down syndrome.

STUDY DESIGN

Nuchal fold thickness was measured at ultrasonographic examination at 14 to 22 weeks' gestation without previous knowledge of the fetal karyotype. Nuchal cystic hygromas were excluded from analysis. Statistical analyses included correlation, logistic regression to control for other ultrasonographic predictors of trisomy 21 and for maternal age, receiver operating characteristic curve, and likelihood ratios (defined as the ratio of the sensitivity to the false-positive rate). P <.05 was considered significant.

RESULTS

Mean gestational age at ultrasonography was 16.9 weeks' gestation (range, 14-22 weeks' gestation). Mean (+/-SD) nuchal fold thickness in fetuses with trisomy 21 (4.7 +/- 1.6 mm; n = 29) was greater than in euploid fetuses (3.2 +/- 0.9; n = 780; P <.001). Logistic regression analysis established that nuchal fold thickness was a significant predictor of trisomy 21 independent both of the other ultrasonographic markers and of maternal age (P <.001). Regression analysis showed that nuchal fold thickness was significantly correlated with gestational age among both fetuses with trisomy 21 and euploid fetuses and that the regression line of fetuses with trisomy 21 had a slope similar to that of euploid fetuses. The difference between observed and expected nuchal fold thicknesses on the basis of the biparietal diameter (as a function of gestational age) was used to obviate the confounding effect of gestational age. Differences between observed and expected nuchal fold thicknesses were then used to calculate likelihood ratios. These likelihood ratios could then be multiplied by the individual prior probability to obtain a patient-specific Down syndrome probability.

CONCLUSION

Nuchal fold thickness is correlated with gestational age in both euploid fetuses and fetuses with Down syndrome. Use of the difference between observed and expected nuchal fold thicknesses to determine likelihood ratios allows the calculation of individual posterior probabilities of Down syndrome that take into consideration both gestational age and maternal age.

Utility of minor ultrasonographic markers in the prediction of abnormal fetal karyotype at a prenatal diagnostic center

OBJECTIVE

This study was undertaken to assess the value of minor ultrasonographic markers in predicting significant karyotypic abnormalities.

STUDY DESIGN

A total of 2743 fetuses (14-24 weeks' gestation) prospectively underwent a detailed ultrasonographic survey before genetic amniocentesis. Criteria for 8 minor ultrasonographic markers were established. Odds ratios for significant karyotypic abnormalities in the presence of minor ultrasonographic markers were calculated with the chi(2) and Fisher exact tests.

RESULTS

Of the fetuses, 14.6% had a single minor ultrasonographic marker, 2.1% had >/=2 minor ultrasonographic markers, and 2.7% had >/=1 major ultrasonographic abnormality. One hundred four fetuses (3.8%) had an abnormal karyotype. Compared with a normal ultrasonographic examination result a single minor ultrasonographic marker increased the risk of karyotypic abnormality 5.7-fold (95% confidence interval, 3.5-9.3), whereas multiple minor markers increased the risk of an abnormal karyotype 12-fold (95% confidence interval, 5.5-26.5). When they were identified ultrasonographically in isolation, echogenic bowel, 2-vessel umbilical cord, echogenic intracardiac foci, choroidal separation, and choroid plexus cysts were statistically associated with an abnormal karyotype. When minor markers were identified in clusters of >/=2, echogenic bowel, short femur, 2-vessel umbilical cord, echogenic intracardiac foci, and mild ventriculomegaly were significantly predictive of karyotypic abnormality. With respect to the a priori aneuploidy risk of 1:26 and the a priori Down syndrome risk of 1:50, a normal ultrasonographic examination result reduced the risks to 1:67 and 1:120, respectively. The use of minor ultrasonographic markers in addition to major ultrasonographic abnormalities increased the detection of karyotypic abnormality from 27.9% to 68.3%. For trisomy 21 the sensitivity rose from 16.4% to 67. 3%.

CONCLUSIONS

Significant karyotypic abnormality risk assessment by ultrasonography was greatly enhanced by the addition of minor ultrasonographic markers. Further, clusters of minor ultrasonographic markers greatly increased the likelihood of karyotypic abnormality compared with a single minor marker. A completely normal ultrasonographic examination result reduced the risk of an abnormal karyotype by 62%. Inclusion of minor ultrasonographic markers in the genetic sonogram in a high-risk population will allow the detection of 68% of fetuses with karyotypic abnormalities with a false-positive rate of 17%.

Noninvasive means of identifying fetuses with possible Down syndrome: a review

Women who are 35 years or older are offered invasive prenatal testing because of the increased risk of chromosomal abnormalities, especially Down syndrome. In an attempt to increase the number of Down syndrome fetuses being detected and decrease the number of invasive procedures being performed on pregnancies not affected with a chromosome abnormality, both biochemical and ultrasound screening methods are being studied and are summarized in this article. The ultrasound markers reviewed include increased nuchal thickness, increased nuchal lucency, shortened femur, shortened humerus, pyelectasis, hypoplastic ears, echogenic intracardiac focus, hypoplasia of the fifth middle phalanx, and echogenic bowel.

Cut-off criteria for second-trimester nuchal skinfold thickness for prenatal detection of Down syndrome in a Thai population

OBJECTIVE

To evaluate the use of progressive cut-offs for nuchal skinfold thickness with advancing gestational age and the commonly applied cut-off method (> 6 mm) for prenatal detection of Down syndrome in a Thai population.

METHOD

A prospective study was performed by experienced perinatologists on 2150 women undergoing second-trimester amniocentesis for the indications of advanced maternal age and past history of chromosomal abnormality. Reference ranges were established for nuchal skinfold thickness from the 16th to the 24th week, using either gestational-specific centiles or the parametric method. Assaying different cut-off criteria for both centile and the parametric methods were calculated and then compared with the commonly applied cut-off level (> or = 6 mm.).

RESULTS

There were 2114 chromosomally normal pregnancies, 19 fetuses with Down syndrome (1:113), and 17 other chromosome abnormalities. In fetuses with normal karyotype the nuchal skinfold thickness increased with advancing gestational age [NF (mm) = -0.502 + 0.212 GA (week), r = 0.36, P < 0.001]. The sensitivities of an abnormal nuchal skinfold thickness using different cut-off criteria for detecting Down syndrome were low (5.3-26.3%) with the false positive rates ranging from 2.5 to 16.5%.

CONCLUSIONS

In this study, measurement of second-trimester nuchal skinfold thickness was a poor and unreliable screening test for fetal Down syndrome in a Thai population.

Obstetric sonography. Who to scan, when to scan, and by whom

Most patients in the United States have an indication for and receive sonography during pregnancy. The issue of routine sonography for low-risk women continues to be contentious even though the randomized trials have not been able to demonstrate a clear benefit. Clinics that routinely offer sonography for all pregnancies usually schedule such a procedure at 16 to 20 weeks of gestation. Although great progress is being made in the first-trimester diagnoses of congenital anomalies, most targeted studies are performed at 18 to 20 weeks of gestation. Although many private obstetricians perform in-office sonography, the highest rates of detection of congenital anomalies are seen in tertiary care settings such as a university medical center. In difficult or otherwise high-risk cases, a consulting perinatologist is commonly the physician most likely to integrate the ultrasound findings with a rational management plan for the remainder of the pregnancy and for delivery.

Screening for the aneuploid fetus

Advances in ultrasound technology have dramatically improved the detection of fetal defects. Although only an invasive test can provide a diagnosis, the incorporation of sonography into current biochemically based screening programs should significantly improve the detection of a host of other physically based fetal abnormalities. This article provides an overview and discussion of the prenatal sonographic features that may suggest the presence of a significant chromosomal abnormality.