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

The likelihood of detecting abnormal karyotypes in fetuses with a single major anomaly or "soft" marker on ultrasonographic scanning

OBJECTIVE

Fetuses with abnormal karyotypes often exhibit distinctive ultrasonographic markers, including major anomalies and "soft" markers, indicating potential chromosomal issues. A crucial consideration arises when a single fetal anomaly is detected, raising the question of whether karyotyping is warranted, given the associated procedural risks. Our objective was to establish correlations between single fetal anomalies identified through ultrasound and chromosomal abnormalities.

METHODS

A cross-sectional study analyzed the karyotype of 1493 fetuses and detected a single ultrasonographic anomaly over a 16-year period. Karyotyping was performed using the standard karyotype technique. Moreover, data regarding the type of anomaly detected ultrasonographically, karyotype results, and outcomes following interventions were collected. Among other methods, the use of positive likelihood ratios (LR+) was used to evaluate the diagnostic accuracy of ultrasound compared to karyotyping.

RESULTS

In total, an aberrant karyotype was identified in 99 fetuses (6.6%). This was most commonly observed in cases involving a "soft" marker, occurring in 27 out of 218 fetuses (12.4%). The most frequently detected aberrant karyotype resulted from aneuploidies (80.6% of cases), notably trisomy 21 (50.5%). "Soft" markers predicted chromosomal issues (LR+ = 1.9; OR = 2.4), and isolated polyhydramnios (LR+ = 1.54; OR = 1.6) showed significance in predicting fetal chromosomal aberrations.

CONCLUSION

When assessing the necessity for karyotyping in fetuses with single major anomalies or "soft" markers, it is crucial to consider individual risks for chromosomopathies, including the LR+ of the detected marker. In cases where fetuses exhibit isolated anomalies with a normal karyotype, additional diagnostic measures, such as molecular cytogenetic and molecular genetics techniques, may become necessary.

Evaluation of chromosomal abnormalities and copy number variations in fetuses with ultrasonic soft markers

BACKGROUND

Some ultrasonic soft markers can be found during ultrasound examination. However, the etiology of the fetuses with ultrasonic soft markers is still unknown. This study aimed to evaluate the genetic etiology and clinical value of chromosomal abnormalities and copy number variations (CNVs) in fetuses with ultrasonic soft markers.

METHODS

Among 1131 fetuses, 729 had single ultrasonic soft marker, 322 had two ultrasonic soft markers, and 80 had three or more ultrasonic soft markers. All fetuses underwent conventional karyotyping, followed by single nucleotide polymorphism (SNP) array analysis.

RESULTS

Among 1131 fetuses with ultrasonic soft markers, 46 had chromosomal abnormalities. In addition to the 46 fetuses with chromosomal abnormalities consistent with the results of the karyotyping analysis, the SNP array identified additional 6.1% (69/1131) abnormal CNVs. The rate of abnormal CNVs in fetuses with ultrasonic soft marker, two ultrasonic soft markers, three or more ultrasonic soft markers were 6.2%, 6.2%, and 5.0%, respectively. No significant difference was found in the rate of abnormal CNVs among the groups.

CONCLUSIONS

Genetic abnormalities affect obstetrical outcomes. The SNP array can fully complement conventional karyotyping in fetuses with ultrasonic soft markers, improve detection rate of chromosomal abnormalities, and affect pregnancy outcomes.

Prenatal genetic considerations in congenital ventriculomegaly and hydrocephalus

BACKGROUND

Fetal ventriculomegaly (VM) is a frequent finding in prenatal ultrasound. Rather than a proper diagnosis, VM is a sonographic sign, making prenatal counseling a complex and challenging undertaking. VM can range from severe pathologic processes leading to severe neurodevelopmental delay to normal variants.

DISCUSSION

A growing number of genetic conditions with different pathophysiological mechanisms, inheritance patterns, and long-term prognosis have been associated both to isolated and complex fetal VM. These include chromosomal abnormalities, copy number variants, and several single gene diseases. In this review, we describe some of the most common genetic conditions associated with fetal VM and provide a simplified diagnostic workflow for the clinician.

No. 261-Prenatal Screening for Fetal Aneuploidy in Singleton Pregnancies

OBJECTIVE

To develop a Canadian consensus document on maternal screening for fetal aneuploidy (e.g., Down syndrome and trisomy 18) in singleton pregnancies.

OPTIONS

Pregnancy screening for fetal aneuploidy started in the mid 1960s, using maternal age as the screening test. New developments in maternal serum and ultrasound screening have made it possible to offer all pregnant patients a non-invasive screening test to assess their risk of having a fetus with aneuploidy to determine whether invasive prenatal diagnostic testing is necessary. This document reviews the options available for non-invasive screening and makes recommendations for Canadian patients and health care workers.

OUTCOMES

To offer non-invasive screening for fetal aneuploidy (trisomy 13, 18, 21) to all pregnant women. Invasive prenatal diagnosis would be offered to women who screen above a set risk cut-off level on non-invasive screening or to pregnant women whose personal, obstetrical, or family history places them at increased risk. Currently available non-invasive screening options include maternal age combined with one of the following: (1) first trimester screening (nuchal translucency, maternal age, and maternal serum biochemical markers), (2) second trimester serum screening (maternal age and maternal serum biochemical markers), or (3) 2-step integrated screening, which includes first and second trimester serum screening with or without nuchal translucency (integrated prenatal screen, serum integrated prenatal screening, contingent, and sequential). These options are reviewed, and recommendations are made.

EVIDENCE

Studies published between 1982 and 2009 were retrieved through searches of PubMed or Medline and CINAHL and the Cochrane Library, using appropriate controlled vocabulary and key words (aneuploidy, Down syndrome, trisomy, prenatal screening, genetic health risk, genetic health surveillance, prenatal diagnosis). Results were restricted to systematic reviews, randomized controlled trials, and relevant observational studies. There were no language restrictions. Searches were updated on a regular basis and incorporated in the guideline to August 2010. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment- related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies. The previous Society of Obstetricians and Gynaecologists of Canada guidelines regarding prenatal screening were also reviewed in developing this clinical practice guideline.

VALUES

The quality of evidence was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care.

BENEFITS, HARMS, AND COSTS

This guideline is intended to reduce the number of prenatal invasive procedures done when maternal age is the only indication. This will have the benefit of reducing the numbers of normal pregnancies lost because of complications of invasive procedures. Any screening test has an inherent false- positive rate, which may result in undue anxiety. It is not possible at this time to undertake a detailed cost-benefit analysis of the implementation of this guideline, since this would require health surveillance and research and health resources not presently available; however, these factors need to be evaluated in a prospective approach by provincial and territorial initiatives.

RECOMMENDATIONS

Evaluation of choroid plexus with fetal magnetic resonance imaging: What happens in ventriculomegaly?

OBJECTIVES

Diagnosis of ventriculomegaly (VM) and identification of choroid plexus (CP) can be challenging with fetal magnetic resonance imaging (MRI). Our aim is to create an adjunct method for supporting the diagnosis of VM by investigating the CP-ventricular wall separation distance in fetuses with and without VM (nV) with fetal MRI.

METHODS

T2-weighted fetal MRIs of 154 fetuses were retrospectively evaluated. The CP separation was defined as the distance between the medial wall of the dependent ventricle and distal tip of the CP glomus. The measurement was performed at the same plane with the dependent ventricle measurement by two blinded readers.

RESULTS

41 fetuses with VM (mean gestational age 27 (19-35 weeks), and 44 nV fetuses (mean gestational age 28 (20-39 weeks) were included. Interobserver reliability was excellent for ventricle diameters (R = 0.99, confidence interval (CI) 95%) and the separation of CP (R = 0.98, CI 95%). Mean distance of CP separation was 10.7 mm ± 4.2 mm and 3.0 ± 1.6 mm in VM and nV fetuses, respectively (p < 0.001). The distance of CP separation to differentiate VM cases was 6.5 mm (sensitivity: 0.98, specificity: 0.98). Separation of CP was correlated to ventricle diameter in cases with (R = 0.674) and without VM (R = 0.805). For the cut-off value >0.65 cm for the distance between the medial wall of the dependent ventricle and the medial border of choroid plexus sensitivity is 97.56, specificity 95.45, positive predictive value (PPV) 95.20, negative predictive value (NPV) 97.70, and likelihood ratio (LR) (+) is 21.46.

CONCLUSION

Fetal CP can be efficiently evaluated with MRI, and the increase of CP-ventricular wall separation distance in correlation with the ventricle diameter is a reliable sign in the diagnosis of fetal VM.

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

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

Choroid plexus separation in fetuses without ventriculomegaly: Natural course and postnatal outcome

PURPOSE

To evaluate fetuses with choroid plexus separation without ventriculomegaly in terms of fetal malformations, behavior of the separation during follow-up, and postnatal outcome.

METHODS

In total, 172 fetuses with choroid plexus separation without ventriculomegaly were included in this prospective study. Fetal sonography was performed at 2- to 4-week intervals, and detailed physical and neurologic examinations were performed after their delivery. Fetuses were categorized into normal and abnormal subgroups according to the outcome.

RESULTS

Sixteen fetuses (9.3%) were included in the abnormal-outcome group and 156 fetuses (90.7%) were included in the normal-outcome group. Both the initial mean lateral ventricular diameter (9.3 mm versus 8.6 mm) and the initial mean choroid plexus separation (4.8 mm versus 3.3 mm) were greater in the abnormal group than in the normal group (p < 0.001 for both comparisons). We found that 4.0 mm was the best cutoff point of choroid plexus separation to detect a major anomaly, with 87.5% sensitivity and 93.6% specificity.

CONCLUSIONS

Choroid plexus separation without ventriculomegaly often resolves within the third trimester and does not affect postnatal outcome. It can be associated with various fetal malformations; however, with a comprehensive examination, all fetal malformations can be detected prenatally. Follow-up sonography studies would be useful, especially in the case of suspected corpus callosum agenesis.

Swedish University Students' Opinion Regarding Information About Soft Markers

The aim of this study was to investigate the opinions of Swedish university students about information regarding soft markers, when observed at second trimester ultrasound screening. A cross-sectional survey, where 85 Swedish university students completed a study specific questionnaire containing eleven hypothetical scenarios, involving various parameters (disease/syndromes/malformations with different characteristics), and location of the markers. Almost all participants indicated that they would wish to be informed, prior to the ultrasound examination, about the assessment and significance of soft markers. However, the number of respondents who requested information about a potential actual finding was considerably less. Several participants wanted to be informed about detected markers associated to serious conditions but not when the marker indicated an increased risk for a treatable disease. Also, the specific location of the marker was of importance to the participants. The majority of respondents wished to be informed about the soft markers if they were observed in the heart or the brain of the foetus, compared to if they were located in the intestine or the skeleton. The students' opinion, in this study, implicate the importance of pre-examination information to enable expectant parents to make informed choice regarding the second trimester ultrasound screening as well as on reciving information of actual findings.

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.

The role of ultrasound in the diagnosis of fetal genetic syndromes

The use of ultrasound in the prenatal diagnosis of fetal genetic syndromes is rapidly evolving. Advancing technology and new research findings are aiding in the increased accuracy of ultrasound-based diagnosis in combination with other methods of non-invasive and invasive fetal testing. Ultrasound as a screening tool for aneuploidy and other anomalies is increasingly being used throughout pregnancy, beginning in the first trimester. Given the number of recorded syndromes, it is important to identify patterns and establish a strategy for identifying abnormalities on ultrasound. These syndromes encompass a wide range of causes from viral, substance-linked, chromosomal, and other genetic syndromes. Despite the ability of those experienced in ultrasound, it is important to note that not all fetal genetic syndromes can be identified prenatally, and even common syndromes often have no associated ultrasound findings. Here, we review the role of ultrasound in the diagnosis of fetal genetic syndromes.

Prenatal screening for fetal aneuploidy in singleton pregnancies

OBJECTIVE

To develop a Canadian consensus document on maternal screening for fetal aneuploidy (e.g., Down syndrome and trisomy 18) in singleton pregnancies.

OPTIONS

Pregnancy screening for fetal aneuploidy started in the mid 1960s, using maternal age as the screening test. New developments in maternal serum and ultrasound screening have made it possible to offer all pregnant patients a non-invasive screening test to assess their risk of having a fetus with aneuploidy to determine whether invasive prenatal diagnostic testing is necessary. This document reviews the options available for non-invasive screening and makes recommendations for Canadian patients and health care workers.

OUTCOMES

To offer non-invasive screening for fetal aneuploidy (trisomy 13, 18, 21) to all pregnant women. Invasive prenatal diagnosis would be offered to women who screen above a set risk cut-off level on non-invasive screening or to pregnant women whose personal, obstetrical, or family history places them at increased risk. Currently available non-invasive screening options include maternal age combined with one of the following: (1) first trimester screening (nuchal translucency, maternal age, and maternal serum biochemical markers), (2) second trimester serum screening (maternal age and maternal serum biochemical markers), or (3) 2-step integrated screening, which includes first and second trimester serum screening with or without nuchal translucency (integrated prenatal screen, serum integrated prenatal screening, contingent, and sequential). These options are reviewed, and recommendations are made.

EVIDENCE

Studies published between 1982 and 2009 were retrieved through searches of PubMed or Medline and CINAHL and the Cochrane Library, using appropriate controlled vocabulary and key words (aneuploidy, Down syndrome, trisomy, prenatal screening, genetic health risk, genetic health surveillance, prenatal diagnosis). Results were restricted to systematic reviews, randomized controlled trials, and relevant observational studies. There were no language restrictions. Searches were updated on a regular basis and incorporated in the guideline to August 2010. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies. The previous Society of Obstetricians and Gynaecologists of Canada guidelines regarding prenatal screening were also reviewed in developing this clinical practice guideline.

VALUES

The quality of evidence was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care.

BENEFITS, HARMS, AND COSTS

This guideline is intended to reduce the number of prenatal invasive procedures done when maternal age is the only indication. This will have the benefit of reducing the numbers of normal pregnancies lost because of complications of invasive procedures. Any screening test has an inherent false-positive rate, which may result in undue anxiety. It is not possible at this time to undertake a detailed cost-benefit analysis of the implementation of this guideline, since this would require health surveillance and research and health resources not presently available; however, these factors need to be evaluated in a prospective approach by provincial and territorial initiatives. RECOMMENDATIONS 1. All pregnant women in Canada, regardless of age, should be offered, through an informed counselling process, the option of a prenatal screening test for the most common clinically significant fetal aneuploidies in addition to a second trimester ultrasound for dating, assessment of fetal anatomy, and detection of multiples. (I-A) 2. Counselling must be non-directive and must respect a woman's right to accept or decline any or all of the testing or options offered at any point in the process. (III-A) 3. Maternal age alone is a poor minimum standard for prenatal screening for aneuploidy, and it should not be used a basis for recommending invasive testing when non-invasive prenatal screening for aneuploidy is available. (II-2A) 4. Invasive prenatal diagnosis for cytogenetic analysis should not be performed without multiple marker screening results except for women who are at increased risk of fetal aneuploidy (a) because of ultrasound findings, (b) because the pregnancy was conceived by in vitro fertilization with intracytoplasmic sperm injection, or (c) because the woman or her partner has a history of a previous child or fetus with a chromosomal abnormality or is a carrier of a chromosome rearrangement that increases the risk of having a fetus with a chromosomal abnormality. (II-2E) 5. At minimum, any prenatal screen offered to Canadian women who present for care in the first trimester should have a detection rate of 75% with no more than a 3% false-positive rate. The performance of the screen should be substantiated by annual audit. (III-B) 6. The minimum standard for women presenting in the second trimester should be a screen that has a detection rate of 75% with no more than a 5% false-positive rate. The performance of the screen should be substantiated by annual audit. (III-B) 7. First trimester nuchal translucency should be interpreted for risk assessment only when measured by sonographers or sonologists trained and accredited for this service and when there is ongoing quality assurance (II-2A), and it should not be offered as a screen without biochemical markers in singleton pregnancies. (I-E) 8. Evaluation of the fetal nasal bone in the first trimester should not be incorporated as a screen unless it is performed by sonographers or sonologists trained and accredited for this service and there is ongoing quality assurance. (II-2E) 9. For women who undertake first trimester screening, second trimester serum alpha fetoprotein screening and/or ultrasound examination is recommended to screen for open neural tube defects. (II-1A) 10. Timely referral and access is critical for women and should be facilitated to ensure women are able to undergo the type of screening test they have chosen as first trimester screening. The first steps of integrated screening (with or without nuchal translucency), contingent, or sequential screening are performed in an early and relatively narrow time window. (II-1A) 11. Ultrasound dating should be performed if menstrual or conception dating is unreliable. For any abnormal serum screen calculated on the basis of menstrual dating, an ultrasound should be done to confirm gestational age. (II-1A) 12. The presence or absence of soft markers or anomalies in the 18- to 20-week ultrasound can be used to modify the a priori risk of aneuploidy established by age or prior screening. (II-2B) 13. Information such as gestational dating, maternal weight, ethnicity, insulin-dependent diabetes mellitus, and use of assisted reproduction technologies should be provided to the laboratory to improve accuracy of testing. (II-2A) 14. Health care providers should be aware of the screening modalities available in their province or territory. (III-B) 15. A reliable system needs to be in place ensuring timely reporting of results. (III-C) 16. Screening programs should be implemented with resources that support audited screening and diagnostic laboratory services, ultrasound, genetic counselling services, patient and health care provider education, and high quality diagnostic testing, as well as resources for administration, annual clinical audit, and data management. In addition, there must be the flexibility and funding to adjust the program to new technology and protocols. (II-3B).

Evaluating the incidence and likelihood ratios for chromosomal abnormalities in fetuses with common central nervous system malformations

OBJECTIVE

To determine the incidence and likelihood ratios for chromosomal abnormalities in fetuses with common central nervous system malformations on ultrasound.

STUDY DESIGN

A database derived retrospective cohort study of all patients referred for ultrasound and genetic evaluation from 1990-2006. Fetal karyotypes were delineated by prenatal diagnosis or postnatal examination. The incidence and likelihood ratios were calculated for the association of each central nervous system abnormality with trisomy 13, 18, and 21.

RESULTS

Of 62,111 women included, 587 (0.9%) had major fetal central nervous system abnormalities. The only central nervous system anomalies associated with trisomy 21 were ventriculomegaly and choroid plexus cysts. When isolated, only spina bifida, holoprosencephaly, and agenesis of the corpus callosum were significantly associated with trisomy 13, anencephaly with trisomy 18, and ventriculomegaly with trisomy 21. Likelihood ratios positive range from 2-20 depending on the central nervous system malformation and aneuploidy type.

CONCLUSION

Central nervous system malformations detected on ultrasound are strongly associated with and predictive of chromosomal abnormalities, especially trisomy 13 and 18.

Anxiety and prenatal testing: do women with soft ultrasound findings have increased anxiety compared to women with other indications for testing?

OBJECTIVE

To determine whether there is a difference in anxiety levels in women referred for soft ultrasound findings, AMA, and abnormal serum marker screens, all of whom have a similar risk for chromosome abnormalities, in order to provide an understanding of patients' anxiety, which may enhance the genetic counseling process.

METHODS

Two self-administered questionnaires were completed after the genetic counseling session. Participants were recruited from multiple prenatal clinics throughout Houston, Texas. The State-Trait Anxiety Inventory Form Y was used to measure anxiety in study participants. Both state and trait anxiety were assessed. Differences between groups were examined using one-way analysis of variance, crosstabulation, chi-square, and Tukey multiple comparisons analysis. A p-value of < 0.05 was considered significant.

RESULTS

Two hundred fifteen women participated in the study: 124 AMA, 55 abnormal maternal serum screens, and 36 soft ultrasound findings. Our findings revealed that women with soft ultrasound findings and abnormal maternal serum screens had significantly higher state anxiety than women who are AMA. State anxiety in women with soft ultrasound findings was not significantly different from women with abnormal maternal serum screens. No significant difference was found between the three groups for trait anxiety. Perceived risk, decision to undergo amniocentesis, education level, and income were factors that significantly affected the women's anxiety scores. However, none of these factors proved to be successful indicators of state or trait anxiety.

CONCLUSION

A woman's referral indication is associated with different levels of anxiety as compared to the actual numerical risk for chromosome abnormalities presented during a genetic counseling session.

Screening for trisomy 21 during the routine second-trimester ultrasound examination in an unselected Chilean population

OBJECTIVE

To evaluate the performance of a detailed ultrasound examination during the second trimester as a screening test for Down syndrome in an unselected Chilean population.

METHODS

This was part of an ongoing longitudinal study. Included were 3071 women with singleton pregnancies who underwent routine ultrasound examination between 21 + 0 and 25 + 6 gestational weeks as a screening test for chromosomal abnormalities and major congenital structural defects, and who were diagnosed as having trisomy 21 or being chromosomally normal. Maternal age, and eight soft markers and cardiac defects associated with Down syndrome were evaluated as a screening test using logistic regression analysis.

RESULTS

The incidence of Down syndrome was 0.6%, and the mean maternal age was 29.4 +/- 6.2 years. At least one of four soft markers (absent nasal bone, nuchal edema, short femur, echogenic foci) and/or cardiac defects was present in 77.8% of Down syndrome fetuses and in 3.1% of normal fetuses. Furthermore, with a false-positive rate of 1%, the detection rate using the combined model of ultrasound markers and maternal age was 72.2%.

CONCLUSIONS

Second-trimester ultrasound markers are able to detect over 70% of Down syndrome fetuses with only a 1% false-positive rate.

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.

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.

Role of second trimester sonography in detecting trisomy 18: a review of 70 cases

PURPOSE

To investigate the role of second-trimester sonographic examination in the prenatal diagnosis of trisomy 18.

METHODS

Out of 22,150 fetal chromosomal analyses performed between 1990 and 2004, 70 trisomy 18 fetuses were found. The sonographic findings of this aneuploidy were analyzed.

RESULTS

The average maternal age was 32.4 years; the average gestational age was 19.5 weeks. Major anomalies were seen in 61 (87.1%) of the 70 fetuses with trisomy 18; among these, cardiac anomalies were the most common (47.1%), with a 27.1% incidence of ventricular septal defects. Anomalies of the central nervous system were seen in 35.7% of cases; abnormal head shape was the most frequently detected anomaly in this group (12.9%). Fifty-six (80%) of the fetuses had at least 1 minor anomaly; of these, choroid plexus cyst was the most common (38.6%). Increased nuchal fold thickness was detected in 17.1% of cases.

CONCLUSION

The vast majority of trisomy 18 fetuses have sonographically detectable abnormalities in the second trimester. Both the 87.1% frequency of major anomalies and the 80% frequency of minor anomalies are substantially higher than multiple biochemical marker tests could achieve. It was also demonstrated that fetal echocardiography plays a pivotal role in the diagnosis of trisomy 18.

Correlation of prenatal sonographic diagnosis and morphologic findings of fetal autopsy in fetuses with trisomy 21

OBJECTIVE

The purpose of this study was to compare the prenatal sonographic and postmortem pathologic findings of fetuses with trisomy 21.

METHODS

Among 22,150 fetal chromosome analyses, trisomy 21 was diagnosed in 207 fetuses between 1990 and 2004. Findings of second-trimester sonography and fetal autopsy were compared by organ system, and their correlation was assigned to 1 of 3 categories.

RESULTS

In total, 83.1% of the 184 fetuses that constituted the final study group had 1 or more abnormal structural findings at postabortion pathologic examination, whereas in 16.9% of the cases, fetal pathologic examination did not reveal any defects in fetal anatomy. Among major structural defects, the agreement between sonographic and autopsy findings was greater than 60% of all abnormalities of these systems: central nervous system (65.4%), heart (67.4%), fetal hydrops (100%), and cystic hygroma (93.3%), whereas the concordance rate was lower in these organ systems: abdominal abnormalities (46.2%), renal anomalies (50%), facial abnormalities (1.2%), and extremities (4.4%). The rate of additional major findings at autopsy was 34.2%. These mainly involved 3 organ systems: heart, head, and abdominal anomalies. Some sonographic findings (n = 16) were not verified at autopsy. The concordances between sonographic and autopsy findings regarding soft markers were considerably high in these markers: increased nuchal fold thickness (72%), short femur/humerus (75%), and pyelectasis (51.9%).

CONCLUSIONS

Examining the correlation between sonography and pathologic findings may indicate possible directions of further development in sonographic screening for trisomy 21. In addition to obstetricians, pediatricians, and geneticists, specialized perinatal pathologists have an important role in the multidisciplinary management of prenatally diagnosed fetal malformations.

Prenatal sonographic findings in 207 fetuses with trisomy 21

OBJECTIVE

The objective was to evaluate the contribution of second trimester ultrasound examination to the prenatal diagnosis of trisomy 21 in 207 fetuses with this aneuploidy. The type and frequency of abnormal sonographic findings were determined. Possible multiple malformation patterns, characteristic of trisomy 21 were sought.

STUDY DESIGN

Singleton fetuses that had prenatal sonography during the second trimester, then underwent cytogenetic evaluation in our institution, made up the study population. The sonographic findings of 207 fetuses with trisomy 21 were analyzed.

RESULTS

Between 1990 and 2004, fetal karyotyping was performed in 22,150 patients for different indications. An abnormal karyotype was diagnosed in 514 cases (2.3%); among them 207 fetuses with trisomy 21 were detected (40.3%). Abnormal sonography was seen in 63.8% of the cases. Structural anomalies were detected in 28.5% of the trisomy 21 fetuses, among them cardiac defects (15.9%), central nervous system anomalies (14.5%), and cystic hygromas (6.8%) were the most common. Of the minor markers, increased nuchal translucency (28%), pyelectasis (20.3%), and shorter extremities (8.7%) were common findings.

CONCLUSIONS

Appropriate diagnosis of structural anomalies, looking for relatively easily detectable minor markers and incorporating fetal echocardiography into the second trimester sonographic protocol, may increase the contribution of mid-trimester ultrasound examination to diagnosing trisomy 21.

[Autopsy findings related to Down's syndrome: 101 cases]

OBJECTIVES

To analyze the spectrum of congenital malformations among fetuses with Down's syndrome sent for necropsy. Materials and methods. Necropsies following medical termination of pregnancy during the second and third trimester were performed during a 4 year period.

RESULTS

The incidence of each malformation was determined. Talipes equinovarus and aberrant lobation of the lung were present in 6% of cases. We are able to state precisely the incidence of 11 pairs of ribs: 11%.

CONCLUSION

A precise knowledge about Down's syndrome associated malformations is essential for genetic counselling. The exact incidence of each sign is important to lead ultrasound examination when this syndrome is revealed.

Isolated choroid plexus separation on second-trimester sonography: natural history and postnatal importance

OBJECTIVE

This study was undertaken to investigate the natural history and clinical importance of choroid plexus separation (a > or = 3 mm distance between the choroid plexus and medial wall of the lateral ventricle) as an isolated finding in the second trimester.

METHODS

This was a 5-year retrospective review of an ultrasound database, looking for singleton fetuses with a menstrual age of 16 to 26 weeks and a finding of isolated choroid plexus separation.

RESULTS

There were 78 cases available for study. The finding of choroid plexus separation was usually transient. Resolution was noted in 37% of the cases that were rescanned within 2 weeks and 71% of the cases that were rescanned more than 2 weeks after the initial diagnosis. Two abnormal karyotypes (trisomy 21 and 47,XXY) and 3 cases with abnormal development not associated with an abnormal karyotype were noted on neonatal follow-up. Cases with abnormal development were quite varied in their presentation.

CONCLUSIONS

The finding of isolated choroid plexus separation is usually temporary, resolving in most cases within 4 weeks of the initial diagnosis. Most infants with this finding have no abnormalities. The clinical implication of the lone case of trisomy 21 was limited by a major preexisting risk in this patient. The 3 cases of abnormal development had varying presentations; the causal nature of this association is not yet clear. No trends were noted between the changing choroid plexus appearance with time and abnormal neonatal outcome, but the number of abnormal cases was quite limited.

Should determination of the karyotype be systematic for all malformations detected by obstetrical ultrasound?

OBJECTIVE

The aim of this study was to determine whether karyotyping should be performed for every fetal malformation detected in low risk populations.

METHODS

A karyotype was obtained from 428 fetuses examined over a 10-year period after fetal malformation was diagnosed using obstetrical ultrasound. These fetuses were separated into two groups, one with isolated malformations and the other with multiple malformations. The association between each type of malformation and the result of karyotype was evaluated.

RESULTS

Forty-eight chromosomal abnormalities were encountered in 428 fetuses (11.2%). The karyotype was abnormal in 32/343 (9.3%) fetuses with isolated malformations and 16/85 (18.8%) fetuses with multiple malformations (p=0.022). The probability of an abnormal karyotype among the group of isolated malformation depended on the anatomical system involved (p<0.001). Our study demonstrated several isolated malformations without chromosomal abnormality (hydronephrosis with high obstruction, unilateral multicystic dysplastic kidney, gastroschisis, intestinal dilatation, meconium peritonitis, cystic adenomatoid malformation, pulmonary sequestration, tumor, vertebral anomaly).

CONCLUSION

Each fetus with multiple malformations needs a chromosomal analysis. Within the group of isolated malformations, our study emphasizes that medical maternal history and the type of malformation need to be taken into account before performing a fetal karyotype.

Prenatal diagnosis of an interstitial 12q chromosome deletion

Rearrangements involving long arm of chromosome 12 are rare events. To our knowledge, we present the first case of an interstitial deletion of the long arm of chromosome 12 in a prenatal diagnosis. A review of the literature is included in our report.

The impact of gestational age on the sonographic detection of aneuploidy

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

[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.

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.

Controversial ultrasound findings

This article has reviewed a few of the more controversial findings in the field of obstetric ultrasound. For each one evidence-based strategies for the management of affected pregnancies have been suggested, derived from what the authors believe is the best information available. In some cases, this information is very limited, which can make counseling these patients extremely difficult. Some physicians find using specific likelihood ratios helpful in these complex discussions. An example of the relative likelihood ratios for several markers of trisomy 21 is illustrated in Table 10. Although the management of each of the findings discussed in this article is different, a few generalizations can be made. To begin with, the detection of any abnormal finding on ultrasound should prompt an immediate detailed ultrasound evaluation of the fetus by someone experienced in the diagnosis of fetal anomalies. If there is more than one abnormal finding on ultrasound, if the patient is over the age of 35, or if the multiple marker screen is abnormal, an amniocentesis to rule out aneuploidy should be recommended. Of the six ultrasound findings reviewed here, the authors believe that only echogenic bowel as an isolated finding confers a high enough risk of aneuploidy to recommend an amniocentesis in a low-risk patient. The other findings in isolation in a low-risk patient seem to confer only a modest increased risk of aneuploidy, if any, and this risk is certainly less than the risk of unintended loss from amniocentesis. Wherever possible, modifiers of this risk, such as maternal age, history, and first and second multiple marker screening, should be used to define more clearly the true risk of aneuploidy. As obstetric ultrasound moves forward, particularly into the uncharted waters of clinical use of three- and four-dimensional ultrasound, one can expect a whole new crop of ultrasound findings with uncertain clinical significance. Clinicians are well advised to await well-designed studies to determine the clinical significance of these findings before altering clinical care.

Intra- and interobserver repeatability of femur length measurement in early pregnancy

OBJECTIVE

To assess the intra- and interobserver reproducibility of songographic measurement of fetal femur length between 10 and 16 weeks of gestation.

METHODS

Femur length was measured three times by the same trained observer in each fetus of 136 pregnant women. A second trained observer then repeated the measurements. The coefficient of variation, intraclass correlation coefficient and repeatability coefficient with 95% CIs were calculated for each observer and between the two observers.

RESULTS

The inter- and intraobserver repeatabilities of femur length were good. For interobserver correlation, the coefficient of variation was 4.6% (95% CI, 3.0-6.2), the intraclass correlation coefficient was 0.82 (95% CI, 0.69-0.95) and the repeatability coefficient was 2.1 (95% CI, 1.8-2.7). For intraobserver correlation, the coefficient of variation was 4.2% (95% CI, 3.2-5.6), the intraclass correlation coefficient was 0.91 (95% CI, 0.75-0.97) and the repeatability coefficient was 3.23 (95% CI, 2.33-3.86) for Observer 2. Similar results were obtained for the other observer.

CONCLUSION

Transvaginal femur length measurement is technically feasible and easy to perform between 10 and 16 weeks of gestation. The high degree of intra- and interobserver repeatability indicates it to be a reproducible method.

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.

Prenatal diagnosis of Down syndrome: ten year experience in the Israeli population

Second trimester maternal serum biochemical markers, introduced between 1990 and 1995, were supplemented with new ultrasound methods at 14-16 weeks and first trimester biochemical markers between 1995 and 2000. This study evaluated the effectiveness of a Down syndrome (DS) prevention program among the Israeli Jewish population between 1990 and 2000. We collected data on the total number of prenatal tests performed on Israeli Jewish women, DS cases detected prenatally and DS livebirths in Israel during these years. We also studied the use of the newer screening tests in 1990, 1992, and 2000. Between 1990 and 1995, use of chromosomal studies for DS in this population increased from 11.3% to 21.6% and the percentage of cases detected prenatally from 53% to 70%. However, between 1996 and 2000, even with the new screening methods, the utilization rate remained similar (20.7% and 19.8%, respectively) and the percentage detected prenatally decreased to 61% in 2000. The total cost per case detected increased from $47,971 US dollars in 1990 to $75,229 US dollars in 1992, and to $190,171 US dollars in 2000. Between 1990 and 1995, improvement in the percentage of cases detected prenatally was associated with a significant increase in the amniocentesis rate-both are attributed to the introduction of second trimester maternal serum biochemical marker tests. Unexpectedly, the introduction between 1995 and 2000 of new genetic methods to assess the DS risk did not improve the percentage detected or reduce the amniocentesis rate, and was accompanied by an increased cost per case detected.

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.

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.

The role of fetal echocardiography in genetic sonography

Genetic sonography identifies between 60% and 93% of fetuses with trisomy 21. One of the reasons for the variation in sensitivity is because of the under-detection of congenital heart defects. Although congenital heart defects are present in 56% of second trimester fetuses and 44% of newborns with trisomy 21, most studies evaluating second-trimester fetuses at risk for trisomy 21 detect less than 10% of heart malformations. This review discusses an approach that allows the fetal sonographer to incorporate fetal echocardiography, based upon the examiner's level of skill and experience, when evaluating the fetus at risk for trisomy 21. The cardiovascular examination consists of three levels. In the Level I examination only noncardiac markers are evaluated for a detection rate of 60% and false-positive rate of 5.9%. The Level II examination incorporates the four-chamber view with non-cardiac markers. If the examiner can identify atrial and/or ventricular chamber disproportion, then the sensitivity is increased to 75%, with a false-positive rate of 6.4%. The Level III examination utilizes grayscale and color Doppler ultrasound to evaluate the fetal heart. If the examiner can identify ventricular septal defects, atrioventricular septal defects, pericardial effusion, tricuspid regurgitation, and chamber disproportion, then the sensitivity of genetic sonography increases to 91% with a false-positive rate of 14%. This review includes Likelihood Ratios for each of the ultrasound markers so that the examiner can compute the risk for trisomy 21 for an individual patient.

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

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

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

OBJECTIVE

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

METHODS

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

RESULT

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

CONCLUSIONS

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

Sonographic findings of the umbilical cord: implications for the risk of fetal chromosomal anomalies

In this review we summarize current knowledge on sonographic findings of the umbilical cord and the risk they impose for chromosomal abnormalities of the fetus. A Medline search of the literature was performed and the pertinent English-language literature was reviewed. Anatomical and Doppler abnormalities of the umbilical cord may be associated with an increased risk of chromosomal aberrations in the fetus. Therefore, level II prenatal sonography should also include a careful examination of the umbilical cord.

Trisomy 21. Second-trimester ultrasound

Not every aspect of sonographic examination reveals karyotypic abnormalities. Ultrasound examination of a fetus with trisomy 21 generally reveals normal amniotic fluid, normal placentation, and normal fetal growth. In addition, other chromosomal abnormalities have many of the same sonographic findings as Down syndrome, and many findings have a large overlap with phenotypically normal fetuses. The importance of second-trimester ultrasound screening for Down syndrome has remained great because of its ease of use and relative effectiveness. Trained sonographers can adjust the relative risk for trisomy 21 and alter the need for genetic amniocentesis. It is important that parents understand the limitations of a screening test and the risks and benefits of possible subsequent confirmatory testing. If a major structural abnormality is identified on ultrasound, karyotype determination should be considered. Nuchal thickness in the first or second trimester remains the most clinically useful marker for trisomy 21. The predictive value of all the markers depends on the population studied and can be modified by a host of biochemical markers and historical factors. If fetal karyotype analysis could be performed without sampling through the uterus, prenatal diagnosis could be offered to all pregnant women, and screening would be unnecessary. Despite its limitations, ultrasound will have an important role in prenatal diagnosis at least until isolating and testing fetal cells from maternal blood or other sources becomes practical and widely available. Whether used alone or in conjunction with additional biochemical or molecular serum markers, ultrasound is an important and powerful tool in prenatal genetic evaluation.

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.

Prenatal ultrasound findings in affected and unaffected pregnancies that are screen-positive for trisomy 18: the California experience

This study investigated whether significant differences in ultrasound findings exist between trisomy 18 affected and unaffected pregnancies positive by serum screening. Ultrasound reports were reviewed for 335 screen-positive women. This represented 65% of all trisomy 18 screen-positive patients who had follow-up services at any of 117 Californian state-approved Prenatal Diagnosis Centers during a six-month period from November 1, 1995 to April 30, 1996. Ultrasound reports were available for 100% of trisomy 18 fetuses diagnosed during the six month period (n=23). Ultrasound findings were reported as normal in 35% of the fetuses affected with trisomy 18. The number and type of abnormalities observed in the affected and unaffected groups are described. When compared to unaffected cases, the trisomy 18 affected fetuses had a greater re-dating discrepancy on follow-up ultrasound evaluation and significantly lower femur length to biparietal diameter (FL/BPD) ratio measurements. We recommend that all women who are screen positive for trisomy 18 be encouraged to have amniocentesis, regardless of ultrasound findings, since affected fetuses may not be detected otherwise.