Association between first trimester absence of fetal nasal bone on ultrasound and Down syndrome

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

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Fetal Nasal Bone Status In Iranian Women Undergoing First-Trimester Screening For Trisomy 21: A Review and an Observational Study

Background:

Failed visualization of the fetal nasal bone (NB) by ultrasound at 11 - 14 weeks of gestation is strongly associated with chromosomal abnormalities. Meanwhile, the incidence of the absent fetal NB in normal fetuses in the first trimester in mothers of different ethnic origins differs significantly. It is, therefore, important to assess ethnic variations in the first-trimester visualization of the fetal NB before introducing this marker into routine screening programs for aneuploidy.

Objectives:

The objectives of this study were to determine the NB length and the prevalence of the NB absence as well as calculating the likelihood ratio (LR) for the absence of the NB in normal fetuses of Iranian women undergoing first-trimester screening for trisomy 21.

Patients and Methods:

In 767 normal fetuses, the fetal profile was examined by ultrasound for the absence/presence of the NB. The NB length was also measured, and the LR for the NB absence was also determined.

Results:

The NB was absent in 2/767 (0.26%) of the fetuses. The mean length of the NB was 3.6 ± 0.69 mm for the fetuses of 11 - 14 weeks gestational age. The LR value of the absent NB was equal to 250 in the normal fetuses of the Iranian population living in the North-West provinces.

Conclusion:

The low prevalence of the NB absence in normal fetuses in the present study is compatible with the larger size of the NB in Iranian people compared to other communities. Meanwhile, the reference range of the NB length in normal Iranian fetuses was established so that basic data could be recorded for further studies regarding the absence or presence of the NB in screening for chromosomal abnormalities (Down syndrome) within the Iranian population.

Prenasal thickness to nasal bone length ratio in normal and trisomy 21 fetuses at 11-14 weeks of gestation

OBJECTIVE

To show the feasibility and to create a reference range for prenasal thickness (PT) and for the PT to nasal bone length (NBL) ratio in normal fetuses at 11-14 gestational weeks and to compare the findings to fetuses with trisomy 21.

METHOD

PT, NBL and PT/NBL ratio were measured retrospectively in stored two-dimensional images of 1155 normal fetuses and 44 fetuses with trisomy 21. Mid-sagittal images were acquired at first trimester ultrasound examinations and were selected from our digital database.

RESULTS

The PT increased with CRL from 1.0 mm at 45-mm CRL to 1.6 mm at 84-mm CRL. The mean PT/NBL ratio was 0.6 and was not altered by CRL. The mean PT/NBL ratio in fetuses with trisomy 21 was significantly higher than in normal fetuses (p < 0.0001). For a cut-off value of 0.8 the PT/NBL yielded a sensitivity of 86.4% and a specificity of 98.4% for trisomy 21.

CONCLUSION

The assessment of PT between 11 and 14 gestational weeks is feasible with high intraclass correlation. The PT to NBL ratio seems to be a promising marker for trisomy 21 in the first trimester and was superior to the isolated contribution of NBL and PT measurements.

Setting up a Nuchal Translucency Clinic: What Radiologists Need to Know

The purpose of this article was to discuss the process of setting up a nuchal translucency (NT) screening clinic in clinical practice, how to interpret the information in combination with other clinical tests, what to do if abnormal results are obtained, and to illustrate some of the fetal anomalies that are associated with an increased NT. The NT was initially implemented to predict the likelihood of a fetus with Down syndrome. Maternal age can be combined with fetal NT and maternal serum biochemistry (free β-hCG and PAPP-A) at 11 to 14 weeks to identify about 90% of affected fetuses. Setting up a clinic to perform the NT screening requires certified physicians and certified sonographers. Certification can be obtained for both physicians and sonographers through Nuchal Translucency Quality Review and Fetal Medicine Foundation. Cell-free DNA testing is now altering what our patients are choosing to evaluate fetuses at risk for chromosomal anomalies and congenital anomalies. Common pitfalls to performing, interpreting, and conveying results of the NT are illustrated in this article. Nasal bone measurement, fetal anatomy examination and fetal echocardiography are tools that add sensitivity to the detection of chromosomal abnormalities. Examples of fetal anomalies discovered during the NT screening are also illustrated. Screening for obstetric complications is an additional benefit to the NT clinic.

Comparative studies of two dimensional and three dimensional ultrasonic nuchal translucency in trisomy assessments

Current two-dimensional (2D) ultrasonic marker measurements are inherent with intra- and inter-observer variability limitations. The objective of this paper is to investigate the performance of conventional 2D ultrasonic marker measurements and proposed programmable interactive three-dimensional (3D) marker evaluation. This is essentially important to analyze that the measurement on 3D volumetric measurement possesses higher impact and reproducibility vis-à-vis 2D measurement. Twenty three cases of prenatal ultrasound examination were obtained from collaborating hospital after Ethical Committee's approval. The measured 2D ultrasonic marker is Nuchal Translucency or commonly abbreviated as NT. Descriptive analysis of both 2D and 3D ultrasound measurement were calculated. Three trial measurements were taken for each method. Both data were tested with One-Sample Kolmogorov-Smirnov Test and results indicate that markers measurements were distributed normally with significant parametric values at 0.621 and 0.596 respectively. Computed mean and standard deviation for both measurement methods are 1.4495 ± 0.46490 (2D) and 1.3561 ± 0.50994 (3D). ANOVA test shows that computerized 3D measurements were found to be insignificantly different from the mean of conventional 2D at the significance level of 0.05. With Pearson's correlation coefficient value or R = 0.861, the result proves strong positive linear correlation between 2D and 3D ultrasonic measurements. Reproducibility and accuracy of 3D ultrasound in NT measurement was significantly increased compared with 2D B-mode ultrasound prenatal assessment. 3D reconstructed imaging has higher clinical values compare to 2D ultrasound images with less diagnostics information.

First-trimester screening for chromosomal abnormalities by integrated application of nuchal translucency, nasal bone, tricuspid regurgitation and ductus venosus flow combined with maternal serum free β-hCG and PAPP-A: a 5-year prospective study

OBJECTIVE

To investigate the performance of first-trimester screening for chromosomal abnormalities by integrated application of nuchal translucency thickness (NT), nasal bone (NB), tricuspid regurgitation (TR) and ductus venosus (DV) flow combined with maternal serum free β-human chorionic gonadotropin (fβ-hCG) and pregnancy-associated plasma protein-A (PAPP-A) at a one-stop clinic for assessment of risk (OSCAR).

METHODS

In total, 13,706 fetuses in 13,437 pregnancies were screened for chromosomal abnormalities during a period of 5 years. Maternal serum biochemical markers and maternal age were evaluated in combination with NT, NT + NB, NT + NB + TR, and NT + NB + TR + DV flow data in 8581, 242, 236 and 4647 fetuses, respectively.

RESULTS

In total, 51 chromosomal abnormalities were identified in the study population, including 33 cases of trisomy 21, eight of trisomy 18, six of sex chromosome abnormality, one of triploidy and three of other unbalanced abnormalities. The detection rate and false-positive rate (FPR) for trisomy 21 were 93.8% and 4.84%, respectively, using biochemical markers and NT, and 100% and 3.4%, respectively, using biochemical markers, NT, NB, TR and DV flow.

CONCLUSION

While risk assessment using combined biochemical markers and NT measurement has an acceptable screening performance, it can be improved by the integrated evaluation of secondary ultrasound markers of NB, TR and DV flow. This enhanced approach would decrease the FPR from 4.8 % to 3.4 %, leading to a lower number of unnecessary invasive diagnostic tests and subsequent complications, while maintaining the maximum level of detection rate. Pre- and post-test genetic counseling is of paramount importance in either approach.

Prenasal thickness-to-nasal bone length ratio: a strong and simple second- and third-trimester marker for trisomy 21

OBJECTIVES

To study the ratio of prenasal thickness (PT) to nasal bone length (NBL) in normal and trisomy-21 fetuses in the second and third trimesters of pregnancy.

METHODS

The PT and NBL were measured retrospectively in 106 normal fetuses (in three-dimensional (3D) volumes) and in 30 fetuses with trisomy 21 (10 on two-dimensional (2D) images and 20 in 3D volumes).

RESULTS

In normal fetuses the mean PT and NBL increased between 15 and 33 weeks' gestation from 2.3 to 6.1 mm (r = 0.85, P < 0.001) and from 3.3 to 9.6 mm (r = 0.87, P < 0.001), respectively. The PT : NBL ratio was stable throughout gestation, with a mean of 0.61 (95% CI, 0.59-0.63; r = - 0.04, P = 0.7). The 5(th) and 95(th) percentiles were 0.48 and 0.80, respectively. In trisomy-21 fetuses the mean PT and NBL increased between 14 and 34 weeks from 3.0 to 9.2 mm (r = 0.86, P < 0.001) and from 1.9 to 7.8 mm (r = 0.85, P < 0.001), respectively. The PT : NBL ratio was significantly higher than in normal fetuses (P < 0.001) but also stable throughout gestation, with a mean of 1.50 (95% CI, 1.20-1.80; r = - 0.35, P = 0.07). Twenty-three (77%) of the 30 fetuses with trisomy 21 had a PT above the 95(th) percentile and 20 (67%) had an NBL below the 5(th) percentile. All the trisomy-21 fetuses had a PT : NBL ratio above the 95(th) percentile. When the 95(th) percentile of the PT : NBL ratio was used as a cut-off value the detection and false positive rates for trisomy 21 were 100 (95% CI, 89-100)% and 5 (95% CI, 2-11)%, respectively. The positive likelihood ratio was 21.2.

CONCLUSIONS

The PT : NBL ratio is stable in the second and third trimesters of pregnancy in both normal and trisomy-21 fetuses, but all trisomy-21 fetuses in this series had a PT : NBL ratio above the 95(th) percentile. The ratio is therefore a strong marker for trisomy 21.

A Thai reference for normal fetal nasal bone length at 11-13(+6) weeks gestation

AIM

The purpose of this study was to establish a Thai reference for normal fetal nasal bone length (NBL) at 11-13(+6) weeks gestation.

METHODS

The fetal nasal bone was measured by sonography in pregnant women at 11-13(+6) weeks gestation. All neonates who showed normal karyotypes were examined after delivery to confirm the absence of congenital abnormalities.

RESULTS

A total of 255 pregnant women were recruited. Forty-seven pregnant women were excluded from the analysis because of technically unsatisfactory examination or absent nasal bone and chromosomal abnormalities. The mean ± SD of NBL was 1.79 ± 0.33 mm and increased significantly with crown-rump length (CRL) and gestational age (p < 0.001). The best-fit equation for NBL in euploid fetuses in relation to CRL was: NBL (mm) = (0.030 × CRL (mm)) - 0.016.

CONCLUSION

NBL in Thai fetuses at 11-13(+6) weeks was found to be on average shorter than that in Caucasian, African-American and Chinese populations, but similar to those reported in Korean and Latin-American populations.

Normative values of fetal nasal bone lengths of Turkish singleton pregnancies in the first trimester

OBJECTIVE

Evaluation of nasal bone improves the performance of first-trimester screening for trisomy 21. In this retrospective study we aimed to determine normative values related to the measurement of nasal bone length of the Turkish population during the first trimester ultrasonographic fetal screening.

MATERIAL AND METHODS

Medical records of singleton pregnancies, whose first trimester fetal screening was performed between 2004 and 2010, were evaluated retrospectively. Pregnancies with any detected/suspicious anatomical or genetic fetal anomalies, biochemical abnormalities, increased nuchal translucency measurements, and pregnancies of artificial reproduction techniques were excluded from data analyses. Mean±standard deviation, median and percentile values of the length of nasal bone were calculated separately for 11(0-6), 12(0-6) and 13(0-6) gestational weeks.

RESULTS

Nasal bone could be visualized in 99.6% of the included 1762 singleton pregnancies. In 16.5% of the cases nasal bones were only noted as present or absent. Mean maternal age was 29.67±4.50 years and mean gestational age was 12.54±0.61 weeks. Median values of nasal bone lengths were 1.7, 1.9, and 2.2 mm for 11(0-6), 12(0-6) and 13(0-6) gestational weeks respectively. Nasal bone length (NBL) increased linearly with advancing gestational age and CRL. NBL (mm)=[0.298xGestational Age (week)]-1.779, R(2)=0.318; p<0.001; NBL (mm)= [0.023 × CRL (mm)] + 0.520, R(2)=0.331; p<0.001.

CONCLUSION

The present study presents normative values of nasal bone in the first trimester screening of normal singleton pregnancies of Turkish population. Nasal bone length increases with advancing gestational age and CRL.

Additional first-trimester ultrasound markers

The first trimester (11-13 +6 weeks) ultrasound examination is useful for several reasons: determination of an accurate date of confinement, diagnostic purposes, and screening for fetal defects. Nuchal translucency measurement combined with maternal serum markers (free b-human chorionic gonadotropin and pregnancy-associated plasma protein A) is the mainstay of first-trimester screening for chromosomal defects. However, over the past decade additional ultrasound markers have been developed that improve the performance of this type of screening. The novel markers include evaluation of the nasal bone, fronto-maxillary angle measurement, and Doppler evaluations of the blood flow across the tricuspid valve and in the ductus venosus.

Prenatal sonographic features of fetuses in trisomy 13 pregnancies. IV

Prenatal ultrasound is a powerful tool to detect structural abnormalities associated with the fetuses in trisomy 13 pregnancies. This article provides a comprehensive review of the prenatal sonographic markers of trisomy 13 in the first trimester, including fetal nuchal translucency thickness, fetal heart rate, fetal nasal bone, fetal tricuspid regurgitation, ductus venous flow, fetal crown-rump length, fetal trunk and head volume, fetal frontomaxillary facial angle, gestational sac volume and umbilical cord diameter, along with biochemical markers such as maternal serum free beta-human chorionic gonadotropin, maternal serum pregnancy-associated plasma protein-A, maternal serum placental growth factor, and the fetal and total cell-free DNA concentration in the maternal circulation.

Nasal bone in prenatal trisomy 21 screening

The definitive diagnosis of fetal chromosomal abnormalities is only accomplished through tests that sample fetal tissue. These procedures--amniocentesis, chorionic villus sampling and cordocentesis--are invasive and carry with them the risks of bleeding, rupture of membranes, and even pregnancy loss. Current recommendations from the American College of Obstetricians and Gynecologists state that all women should be offered screening, regardless of maternal age. However, the exact screening test to apply to pregnant women is still a matter of debate. The goal of any screening method should be high detection (sensitivity) at low screen positive rates. Recent attention has focused on additional ultrasound markers to potentially improve the detection rate. Given that mid-face hypoplasia and a flattened nose are characteristic features of Down syndrome, investigators have tried to utilize its prenatal appearance--or more specifically, its absence--to enhance the detection of trisomy 21 (T21). The purpose of this document is to review the data on the utility of the nasal bone as a marker for T21. Particular attention will focus on its use in the first trimester versus second trimester as well as future directions for its potential incorporation into screening strategies.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to relate the prenatal and postnatal nasal phenotypes for Down syndrome, identify the potential role and pitfalls of nasal bone characteristics in screening for Down syndrome, and describe 3 different methods to define fetal nasal bone hypoplasia.

Prenatal ultrasound diagnosis in 51 cases of holoprosencephaly: craniofacial anatomy, associated malformations, and genetics

OBJECTIVE

To analyze the prenatal ultrasound findings of the craniofacial and extracephalic anatomy, the postnatal pathological findings, and the genetic anomalies in 51 cases of holoprosencephaly (HPE).

MATERIALS AND METHODS

Between 1990 and 2005, a collective of 51 fetuses with tentative ultrasound diagnosis of HPE was recruited at two tertiary referral centers for prenatal ultrasound diagnostics via the Pia Fetal Database (GEMedical Systems, Webling, Germany). Cephalic as well as extracephalic anomalies were investigated, and all cases were subdivided into the subgroups lobar, a lobar, and semilobar HPE. In addition to the ultrasound investigation, 45 fetuses were analyzed for genetic anomalies and 21 fetuses underwent an autopsy.

RESULTS

The average age at diagnosis was 21.9 weeks of gestation. There was a greater number of female fetuses, with an overall ratio of 2.67:1. In 61% of all cases, there was a reduction of growth in comparison with healthy fetuses of the same age. Within the second trimenon, the cephalic anomalies became evident when investigating the diameter of the fetal head (second trimenon: 71%below the fifth percentile; third trimenon: 92% below the fifth percentile). In 82%of the cases, extracephalic anomalies were diagnosed additionally. In 63%, the diagnosis of holoprosencephaly led to a termination of pregnancy. Ten percent of the fetuses were born alive. In 81% of the cases, the diagnosis of HPE was confirmed postnatally. The remaining 19% showed other severe cephalic and extracephalic anomalies. Chromosomal anomalies were detected in 79% of the fetuses, most frequently trisomy 13 (59%).

DISCUSSION

Because of recent advances in the development and improvement of high-resolution ultrasound, early diagnosis of congenital anomalies such as HPE is now possible. In this study, which represents the largest collection of prenatally diagnosed HPE reported in the literature to date, the average age at diagnosis was earlier than in other studies. The ultrasound devices of today provide excellent images of the fetus that allow an exact diagnosis of craniomaxillofacial anomalies as well as extracephalic anomalies. Apart from a very few cases, the diagnosis of HPE is incompatible with life.

First Trimester Ultrasound Screening: An Update

For many years, the main use of ultrasound in the first trimester of pregnancy was to confirm viability and to establish gestational age. Indeed, the crown-rump length measurement in the first trimester remains the most accurate method to estimate the gestational age even today. However, improvements in ultrasound equipment and improvement in our understanding of normal and abnormal fetal development allows us now to perform a much more complete first trimester fetal evaluation. This pertains not only to the diagnosis of fetal anomalies but also to screening for fetal defects. The combination of the nuchal translucency measurement and maternal serum biochemistries (free β-hCG and PAPP-A) has been shown to be an extremely efficient way to screen for fetal aneuploidy. The addition of other first trimester markers such as the nasal bone evaluation, frontomaxillary facial angle measurement, and Doppler evaluation of blood flow across the tricuspid valve and through the ductus venosus improves the screening performance even further by increasing the detection rates and decreasing the false positive rates. Several of the first trimester markers also are useful in screening for cardiac defects. Furthermore, significant nuchal translucency thickening has been associated with a variety of genetic and nongenetic syndromes. A recently described first trimester marker called the intracerebral translucency appears to hold great promise in screening for open spine defects. Finally, it appears that a first trimester evaluation (uterine artery Doppler and the measurement of certain biochemical markers in the maternal serum) significantly improves the assessment of the risk of preeclampsia.

Prenatal screening for chromosome abnormalities in a region with no access to termination of pregnancy

OBJECTIVE

To analyze the different variables that affect couples' decision-making about prenatal screening of chromosome abnormalities in a population with limited access to prenatal diagnosis and no legal termination of pregnancy (TOP).

METHODS

From February through August 2004, 79 couples who requested for prenatal screening at centers from Argentina and Uruguay participated in a study. A cross-sectional survey was administered to assess attitudes toward prenatal screening, the decision-making process, and knowledge and attitudes toward TOP.

RESULTS

Mean maternal age was 32.8 +/- 0.4 years. Among the couples, 88.61% knew that TOP due to fetal anomalies is not legal in their countries. When asked about the possibility of TOP in case of a serious fetal anomaly, 53% would contemplate this option.

CONCLUSION

Prenatal screening is a common practice worldwide. However, unlike most developed countries, our region has a limited access to prenatal diagnosis and no legal TOP. Those couples who stated that 'reassurance about fetal well-being' was the most important reason to perform prenatal screening had more positive attitudes toward TOP than those who considered this screening important 'to be better prepared to receive the baby'. Our findings can be used to inform and revise current health-care policies.

Fetal nasal bone status in Chinese women undergoing first-trimester screening for trisomy 21

OBJECTIVE

The objective of the study was to determine the likelihood ratio for trisomy 21 in Chinese fetuses with absent nasal bone (NB) at 11-14 weeks of gestation.

STUDY DESIGN

The NB was classified as present or absent in 8101 chromosomally/phenotypically normal or trisomy 21 pregnancies. The effect of crown rump length (CRL), nuchal translucency (NT), maternal age, and fetal karyotype on the incidence of absent NB was examined using logistic regression.

RESULTS

The NB was successfully examined in 7925 cases (97.8%). The incidence of absent NB in unaffected and trisomy 21 cases were 2.1% (164/7899) and 50% (13/26), respectively. CRL (odds ratio [OR], 0.9; 95% confidence interval [CI], 0.87-0.92), NT (OR, 1.7; 95% CI, 1.4-2.3), and trisomy 21 (OR, 22.3; 95% CI, 8.1-61) were significant independent predictors of likelihood of absent NB. Positive likelihood ratios (LR) for trisomy 21 in Chinese were lower than that of Caucasians for the equivalent CRL and NT measurements.

CONCLUSION

Estimated risk for trisomy 21 in Chinese incorporating nasal bone status should use LRs derived in Chinese rather than Caucasians.

Fetal nasal bone length and Down syndrome during the second trimester in a Chinese population

OBJECTIVE

The purpose of the present study was to build a database of reference ranges of fetal nasal bone length (NBL) in a Chinese population. The accuracy rate of detecting Down syndrome was also analyzed using fetal NBL as a marker.

METHODS

The control group of fetuses included 342 normal singleton pregnancies with no chromosomal or congenital anomalies. The present study was a cross-section study and the control group was used to construct percentile values of NBL from 13 to 29 gestational weeks of age. Two-dimensional ultrasonography was used for the nasal bone studies. Measurements of NBL were collected and each fetus contributed a single value to the reference sample. During the study period, 14 fetuses with Down syndrome were examined. Measurement of fetal NBL was made during amniocentesis, with gestational age ranging from 13 to 19 weeks.

RESULTS

From 342 normal fetuses with gestational age ranging from 13 to 29 weeks, reference ranges of NBL were constructed. The reference ranges were constructed from the 100(1 - p)% reference range: Y +/- Zp x square root sigma 2, where Y = 25 - exp(3.58 - 0.044 x t + 0.0006 x t2), with Y being the fitted mean of regression model and t being gestational age (weeks). Using fetal NBL, the regression model was Pr(Down syndrome) = exp(W)/ [1 + exp(W)], where W = 0.62-4.80 x NBL (multiples of the median) in predicting Down syndrome. Fetal NBL was found to have a sensitivity and specificity of 0.78 and 0.78, respectively, in predicting Down syndrome in the second trimester of pregnancy.

CONCLUSIONS

Fetal NBL measurement can provide a simple and useful algorithm to predict Down syndrome during the second trimester of pregnancy.

Medida do comprimento do osso nasal entre 11 e 15 semanas de gestação em uma população brasileira: estudo preliminar

OBJETIVO: Determinar valores de referência para o comprimento do osso nasal entre 11 e 15 semanas de gestação em uma população brasileira. MATERIAIS E MÉTODOS: Realizou-se estudo de corte transversal com 171 gestantes normais entre 11 e 15 semanas completas. O osso nasal foi medido por via transabdominal em todos os casos. Foram calculados os percentis 5 a 95 para o comprimento do osso nasal pela fórmula: média ± 1,645 desvio-padrão. Para avaliar a correlação do comprimento do osso nasal com parâmetros antropométricos fetais utilizou-se o coeficiente de correlação de Spearman, com intervalo de confiança de 95%. RESULTADOS: O osso nasal foi mensurado em todos os casos, sendo que o comprimento médio variou de 1,69 mm a 2,94 mm. O comprimento do osso nasal mostrou-se fortemente correlacionado com todos os parâmetros antropométricos fetais (p < 0,001) e com a idade gestacional (R² = 0,59). CONCLUSÃO: Apesar de ser um estudo preliminar, a curva de referência do comprimento do osso nasal foi estabelecida.

Fetal nasal bone assessment in first trimester down syndrome screening

OBJECTIVE

To evaluate the contribution of nasal bone assessment in the first trimester Down syndrome screening.

METHODS

The fetuses which underwent first trimester screening with nuchal translucency (NT) measurement were evaluated for the absence or presence of nasal bone according to the instructions described by the Fetal Medicine Foundation, London.

RESULTS

Among the 1,807 fetuses included in the study, 9 had trisomy 21. The detection rate of Down syndrome with NT measurement was 77.8% (7/9) with a false-positive rate of 4.5%. Incorporation of biochemical tests (PAPP-A, and free beta-hCG measurement) into the screening increased the detection rate to 88.9% (8/9) and decreased the false-positive rate to 3.6%. The prevalence of absent nasal bone was 7/1,798 (0.39%) in chromosomally normal fetuses, and 3/9 (33.3%) in Down syndrome fetuses. Sensitivity, specificity, positive predictive and negative predictive values of absence of nasal bone for trisomy 21 are 33.3% (CI: 0.12-0.64), 99.6% (CI: 0.99-0.99), 30% (95% CI: 0.11-0.53) and 99.7% (95% CI: 0.99-0.99), respectively. The positive likelihood ratio of absent nasal bone was 85.6 (95% CI: 26.2-279.5), and the negative likelihood was 0.67 (95% CI: 0.42-1.06). When nasal bone assessment was incorporated into the NT risk assessment or combined test, the detection rate of trisomy 21 was not changed, however, the false-positive rate decreased to 3.4 and 3%, respectively.

CONCLUSION

The absence of fetal nasal bone has a high positive likelihood ratio for Down syndrome in the first trimester screening, and the presence of nasal bone may potentially lower the need for invasive testing.

Estudo da translucência nucal, ducto venoso, osso nasal e idade materna na detecção de cromossomopatia fetal em uma população de alto risco

OBJETIVO: Avaliar a translucência nucal, o ducto venoso, o osso nasal e a idade materna > 35 anos como testes de rastreamento para aneuploidias entre 12 e 14 semanas de gestação em pacientes de alto risco. MATERIAIS E MÉTODOS: Estudo prospectivo observacional envolvendo 92 gestantes entre 12 e 14 semanas submetidas a biópsia de vilo corial por alto risco de trissomia, baseado na medida da translucência nucal (17,4%) e idade materna >35 anos (78,3%). Antes da biópsia de vilo corial, realizaram-se medida da translucência nucal, avaliação de fluxo no ducto venoso e identificação do osso nasal. Calcularam-se a sensibilidade, a especificidade, o valor preditivo positivo e o valor preditivo negativo para testes realizados em paralelo e em seqüência. RESULTADOS: Encontrou-se alteração cromossômica em 12 (13,5%) fetos; 7 (58,3%) apresentavam trissomia 21. Osso nasal foi identificado em todos os fetos com trissomia. Translucência nucal, ducto venoso e idade materna isolados mostraram baixa sensibilidade (41,67-58,33%) e baixo valor preditivo positivo (10-45,45%). A associação translucência nucal + ducto venoso + idade materna apresentou o melhor resultado (sensibilidade: 100%; especificidade: 6,49%; valor preditivo positivo: 14,29%; valor preditivo negayivo: 100%). CONCLUSÃO: Em gestantes com idade > 35 anos, a associação translucência nucal + ducto venoso mostra-se como a mais sensível para a indicação de procedimento invasivo.

Ethnic variation and variability of fetal nasal bone length at 11-15 weeks of gestation in a Brazilian population: preliminary results

OBJECTIVE

To evaluate the maternal ethnic influence and the intra and interobserver reproducibility of the nasal bone length measurement at 11-15 weeks of gestation in a Brazilian population.

METHODS

A cross-sectional study with 171 normal pregnant women at 11-15 weeks was performed. Nasal bone was transabdominally measured in all cases. The patients were separated into three racial groups (White, Black and Asian) according to maternal ethnicity. The intraobserver variability was calculated through the repeated measurement of 55 fetuses by a single observer, and the interobserver variability was calculated through 44 measurements by two observers. The ANOVA test was used to compare the three racial groups. To calculate the variability, the intraobserver correlation coefficient (intra-CC), the interclass correlation coefficient (inter-CC) with 95% confidence interval, and the Bland-Altman plots were used.

RESULTS

No statistically significant difference could be observed among the three races as for nasal bone length measurement (P = 0.934). The intraobserver variability was considered very good [intra-CC 0.92-IC 95% (0.902; 0.947)], as well as the interobserver variability [inter-CC 0.91-IC 95% (0.873; 0.940)].

CONCLUSIONS

There is no significant difference in nasal bone length measurement among the three races analyzed. Nasal bone length measurement is reproducible.

The use of nuchal translucency in contemporary obstetric practice

Nuchal translucency sonography is the most powerful single prenatal marker for Down syndrome. Its detection rate is 75% at a 5% false-positive rate. The combination of nuchal translucency and maternal serum-free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A can identify 85% to 90% of fetuses with Down syndrome for a false-positive rate of 5%. This method can also identify more than 90% of fetuses with trisomies 18 and 13, Turner syndrome, and triploidy for a screen-positive rate of 1%.

Likelihood ratios for fetal trisomy 21 based on nasal bone length in the second trimester: how best to define hypoplasia?

OBJECTIVE

To determine the best measure of fetal nasal bone hypoplasia for trisomy 21 risk assessment in the second trimester.

METHODS

This was a prospective, observational study performed at a single institution between February 2003 and December 2005. Fetuses with nasal bone length recorded sonographically between 16 and 20.9 weeks and known karyotype were included. Definitions of nasal bone hypoplasia assessed included: non-visualized nasal bone, nasal bone < 10th percentile, nasal bone < 2.5th percentile, biparietal diameter/nasal bone ratio >or= 10 and >or= 11 and nasal bone multiples of the median (MoM) <or= 0.5, <or= 0.6, and <or= 0.7.

RESULTS

A total of 371 chromosomally normal and 11 trisomy 21 fetuses were included. Nasal bone hypoplasia based on MoM was superior to the other measures of hypoplasia for trisomy 21 risk assessment as reflected by a higher positive likelihood ratio. The risk for fetal trisomy 21 was higher with greater degrees of nasal bone hypoplasia.

CONCLUSION

Hypoplasia, as defined by MoM, is the superior approach when incorporating nasal bone evaluation into fetal trisomy 21 risk assessment in the second trimester.

First-trimester ultrasound assessment of the nasal bone to screen for aneuploidy

Increasingly, women are choosing first-trimester risk assessment for Down syndrome and other aneuploid conditions. Recent studies have suggested that adding ultrasound assessment of the nasal bone to nuchal translucency thickness and maternal serum analytes in the first trimester will improve performance. This report assesses the current literature and discusses practical issues that must be addressed before widespread implementation of nasal bone screening in the United States.

Mid-facial anthropometry in second-trimester fetuses with trisomy 21: a three-dimensional ultrasound study

OBJECTIVES

The aim of this study was to evaluate whether fetuses with trisomy 21 and detectable nasal bones have a distinct facial anthropometry that can be objectively defined using three-dimensional (3D) ultrasonography.

METHODS

A prospective cross-sectional study of 40 fetuses in the second trimester, 17 with trisomy 21 and 23 controls, was performed. The 3D volume datasets of each case were evaluated for documentation of the nasal bones using the multiplanar and the maximum mode. The nasal bone length and the angle formed by the two maxillary bones at the level of the frontal process were then measured.

RESULTS

The nasal bones were absent in 7 (41%) of the 17 fetuses with Down syndrome. All of the 23 normal fetuses had detectable nasal bones. The difference between nasal bone length in trisomy 21 fetuses and controls did not reach statistical significance (p = 0.087). The mean maxillary angle in trisomy 21 fetuses with nasal bones was significantly wider compared to controls (p = 0.029).

CONCLUSIONS

The nasal bones are present in the majority of fetuses with trisomy 21 in the second trimester. This group of fetuses has a characteristic mid-facial anthropometry (wider maxillary angle) that can be assessed by means of 3D ultrasonography.

Ultrasonographic evaluation of fetal nasal bone in a low-risk population at 11-13 + 6 gestational weeks

OBJECTIVE

To evaluate the utility of determining the presence/absence of nasal bone in a low-risk fetal population.

METHODS

Prospective study of the presence/absence of nasal bone among 1800 consecutive unselected fetuses, with complete follow-up of results.

RESULTS

An adequate sonographic evaluation of nasal bone was obtained in 1682 (93.44%) of the fetuses. Nasal bone was considered absent in 19 (1.06%) of 1790 fetuses with a normal karyotype and in 2 (28.57%) of the seven recorded cases of Down syndrome (DS). The overall first-trimester sensitivity for DS to the absence of nasal bone was two of the six cases (33.3%) and the false-positive rate was 1.13%. The positive predictive value for DS of the absence of nasal bone was 2/21 (9.52%).

CONCLUSIONS

In a low-risk population, the evaluation of the presence/absence of nasal bone in DS screening during the first trimester has a low sensitivity. First-trimester assessment of the nasal bone in population screening may play a lesser role than in the re-evaluation of high-risk pregnancies.

First-trimester ultrasonographic screening for trisomy 21 using fetal nuchal translucency and nasal bone

OBJECTIVE

To report our experience with first-trimester screening for trisomy 21 by using the combination of nuchal translucency thickness and nasal bone assessment.

METHODS

Pregnant women from a predominantly Latin American population consisting of patients at both low risk and high risk for chromosomal defects underwent first-trimester ultrasonographic screening. Nuchal translucency thickness and nasal bone were assessed by two accredited fetal medicine specialists. Cases of trisomy 21 were identified from the cytogenetics laboratory logbook.

RESULTS

Over a 3-year period, 1,287 consecutive singleton pregnancies were screened. The median maternal age was 33 years (range 14-47 years), with 456 (35.4%) women aged 35 years or older at the time of the scan. Overall, 110 fetuses (8.5%) had nuchal translucency thickness greater than the 95th percentile for gestational age and 25 (1.9%) had absent nasal bone. Trisomy 21 was diagnosed in 31 cases. Among them, the nuchal translucency thickness was increased in 28 and the nasal bone was absent in 13 (detection rates of 90.3% and 41.9%, respectively; P<.01). All but one (92.3%) of the trisomy 21 fetuses with absent nasal bone had increased nuchal translucency. Only two of the normal fetuses had an absent nasal bone in the first trimester.

CONCLUSION

In our population, increased nuchal translucency thickness is the most important ultrasonographic marker of trisomy 21. In contrast, the nasal bone seems to have a less prominent role in identifying the fetus at risk for trisomy 21 due to its lower detection rate. However, an absent nasal bone should be considered as a highly predictive marker of trisomy 21.

Nuchal Translucency and First Trimester Risk Assessment

First-trimester risk assessment for fetal aneuploidy using nuchal translucency (NT) measurement is rapidly gaining popularity in the United States. In combination with maternal serum markers in the first trimester, the screening performance is exceptionally good, with detection rates of more than 80% at a screen positive rate of 5%. Recently, the method has been validated for screening for Down syndrome and other aneuploidies in multicenter trials in the United States and elsewhere. Compliance with established criteria for measurement of the NT is essential to achieve uniform reliability and high screening test sensitivity. There is an international consensus about the importance of specific training in the NT examination, conformity to standards of NT measurement, and regular audit for quality assurance. In the United States, the Nuchal Translucency Quality Review program has been developed to administer credentialing and quality review for registered practitioners. The Nuchal Translucency Quality Review credentials signify the proficiency of the sonographer or sonologist in NT measurement and participation in a regular quality assurance audit. We encourage accreditation of clinical sites offering first-trimester risk assessment to ensure the highest quality care.

First trimester ultrasonography in screening and detection of fetal anomalies

An obstetrical ultrasound examination provides invaluable information regarding the fetus. Until the mid-1980s, ultrasound in the first trimester was limited to localization of the pregnancy, establishing viability, and accurate dating. With the advent of high-resolution ultrasound and transvaginal scanning, a significant amount of information about the fetus can be gained and provided to the patient at a very early stage in gestation. This article provides an overview of the role of first trimester (11-13 + 6 weeks' gestation) ultrasound in screening and diagnosis of fetal anomalies. The first trimester is an ideal time for screening for aneuploidy, primarily due to the advantages that nuchal translucency (NT) measurement provides. NT measurement is also useful in establishing the risk of congenital cardiac disorders and a number of genetic and non-genetic syndromes. Significant NT thickening is associated with an increase in perinatal morbidity and mortality. Potential mechanisms resulting in increased NT are discussed. A number of new ultrasound markers for fetal aneuploidy have been investigated over the past several years, some of which appear to improve the screening efficacy of early ultrasonography. The role of these is reviewed. A number of fetal anomalies can now be consistently diagnosed in the first trimester. Their appearance at this early gestational age is discussed as well. It is clear that, data obtained by first trimester ultrasound are useful in counseling expectant parents and in planning the appropriate follow-up.

Awareness and attitude toward prenatal diagnosis of chromosomal abnormalities in patients with no access to legal termination of pregnancy

OBJECTIVE

To analyze variables affecting couples' decision making about prenatal cytogenetic diagnosis in patients with no access to legal termination of pregnancy (TOP).

METHODS

Patients undergoing invasive prenatal diagnosis were anonymously surveyed after counseling and before the procedure. The questionnaire enquired about sociodemographic features, medical history, knowledge of and attitudes toward genetic testing and TOP.

RESULTS

Two genetic units distributed 372 questionnaires. Mean maternal age was 36 +/- 4 years. Access to prenatal genetic counseling was mainly patient's own initiative, or 'self-referral'. Most self-referred patients (87%) considered that 'receiving accurate information' was the main issue. Eighty-one per cent of all couples knew that TOP because of fetal anomalies was not legal. In case of a serious anomaly, 68.2% of patients would contemplate TOP, in spite of the risk of being exposed to an unsafe abortion.

CONCLUSIONS

In many countries, prenatal genetic testing is offered, but TOP is not available. In the present study, although most of the couples who decided to undergo prenatal genetic testing were aware of this, they still chose to perform prenatal diagnosis. The main reason given was to obtain reliable information about fetal condition. Finally, if a fetal chromosomal abnormality were detected, most of them would consider TOP.

First-trimester screening

Screening for fetal chromosome abnormalities, particularly for trisomy 21, has made dramatic advances. Better screening demonstrates that "high-risk" patients--particularly over age 35--can have lower risk of defects than younger unscreened women. This has caused reduction of amniocentesis for older patients and made screening available for younger patients who have the universal 2% to 3% risk. This means lower procedural-related losses of normal fetuses, and better resource allocation. The trend toward first-trimester detection of structural defects continues; a normal survey is reassuring and helps exclude major defects. Based on screening results, patients can be triaged into early follow-up and possible amniocentesis as 14 to 16 weeks, or a later detailed anatomic survey at 18 to 20 weeks.

Ultrasonographic measurement of fetal nasal bone length in the second trimester in Korean population

OBJECTIVE

To establish the reference range of fetal nasal bone length (NBL) in the second trimester in the Korean population and to determine its clinical value in screening for trisomy 21.

STUDY DESIGN

A total of 3019 consecutive fetuses at 16-28 weeks of gestation underwent ultrasonographic measurement of NBL at Asan Medical Center from October 2003 to August 2005.

RESULTS

Fetal profile was successfully examined in 95.6% (2885/3019) of the fetuses. NBL increased linearly with advanced gestation (R(2) = 0.4337, p < 0.001). During this period, 23 fetuses with chromosomal abnormalities (including nine with trisomy 21, two with trisomy 18, and three with Turner syndrome) were detected. In trisomy 21, hypoplastic nasal bone (<2.5th percentile) was seen in 3/9 fetuses, and the NBL of one fetus was between the 2.5th and 5th percentile. Hypoplastic nasal bone was seen in 3.1% (89/2833) of fetuses with normal chromosomal or postnatal examination findings.

CONCLUSION

We present the normal range of NBL in the second trimester in the Korean population and also their linear relationship with gestational age (GA). The NBL appears to be shorter in Korean fetuses than Caucasian and Chinese fetuses. This indicates that the normal range would vary between races and that a relative percentile is a more reliable screening criterion than an absolute value.

First-trimester examination of fetal nasal bone in the Chinese population

OBJECTIVES

Absence of the nasal bone in fetuses with trisomy 21 is a potential ultrasound marker for Down syndrome from the first trimester onwards. Racial differences in fetal nasal bone length have been reported. There was no reference range for the first-trimester fetal nasal bone length (NBL) in the Chinese population.

METHODS

From January 2002 to February 2005, we investigated the reference range of NBL in 2169 singleton fetuses whose parents were Chinese with normal pregnancy outcome. Ultrasound measurements of NBL were performed on a midsagittal plane at 12-14 weeks' gestation.

RESULTS

The nasal bone length measurement showed a significant increase with gestational age (GA) (p < 0.05). A linear relationship between nasal bone length and gestational age (NBL = -3.3462 x GA + 0.627, R(2) = 0.30, p < 0.001) as well as a linear relationship between nasal bone length and crown-rump length (CRL) (NBL = 0.3741 x CRL + 0.284, R(2) = 0.30, P < 0.001) was established.

CONCLUSION

The measurement of nasal bone length was feasible in the first trimester. The reference range of NBL in normal Chinese fetuses in the first-trimester of pregnancy was established. This formed a basis for further study on the use of fetal nasal bone measurement in the screening for aneuploidy in the Chinese population.

Nasal bone length at 11-14 weeks of pregnancy in the Korean population

OBJECTIVES

The aim of this study was to provide reference values for nasal bone length (NBL) scanned at 11-14 weeks' gestation in the Korean population and compare these values with those of the Caucasian and African-American populations.

METHODS

From April 2004 to July 2004, fetal NBLs were measured in well-dated, non-anomalous fetuses at 11-14 weeks' gestation in the Korean population. Regression analysis was used to assess the relationship between NBL and crown-rump length (CRL), and reference values including the 5th, 50th, and 95th percentile were calculated for each gestational age. The reference values in our study were compared with those of the Caucasian and African-American populations.

RESULTS

A total of 982 cases were prospectively included in the study. NBL increased linearly with advance in CRL and was described by the equation; NBL (mm) = 0.433 + 0.022 x CRL (mm), R(2) = 0.37. The median values (5%, 95%) were 1.5 mm (1.2 mm, 1.9 mm), 1.7 mm (1.4 mm, 2.1 mm), 1.9 mm (1.6 mm, 2.3 mm), and 2.1 mm (1.7 mm, 2.6 mm) for 11, 12, 13, and 14 weeks' gestation, respectively. The median values for each gestational age in the Korean population were significantly lower than those in the Caucasian and African-American populations (P < 0.0001).

CONCLUSION

There is a difference in NBL scanned at 11-14 weeks' gestation between the Korean and the Caucasian/African-American populations, and so racial adjustment is needed in the evaluation of the fetal nasal bone for current first-trimester screening.

Nasal bone assessment in prenatal screening for trisomy 21

A small nose is a common facial feature of individuals with trisomy 21. Evidence based on radiologic, histomorphologic, and sonographic studies shows that nasal bone abnormalities are significantly more common in trisomy 21 fetuses than in euploid fetuses. These abnormalities, which include both nasal bone absence and short nasal bone length, can be detected by prenatal ultrasound. In this article we review the evidence and discuss the potential value of assessment of the fetal nasal bone in screening for trisomy 21.

Interest of foetal nasal bone measurement at first trimester trisomy 21 screening

OBJECTIVES

The purpose of this study is to assess the feasibility of foetal nasal bone (NB) measurement during the first trimester of pregnancy, and to examine the contribution of this measurement to the prenatal screening for Down syndrome following the definition of NB threshold using ROC curves in an unselected population.

METHODS

This prospective study was carried out at our centre SIHCUS-CMCO (reference centre) from January 2002 to December 2004 on a total of 2,044 pregnant outpatients at gestational weeks 11-14. Only 1260 singleton foetuses were used for statistical analysis. In the 784 other patients, we were unable to obtain a correct image allowing a reproducible measurement. NB was measured during the same session as nuchal translucency (NT) measurement. Ten trained sonographers took part in the study. Correlation index was evaluated to shed light on a link between interest variables and NB. Screening values of NB measurement in T 21 were also calculated with NB measurement according to crown-rump length, and expressed as the best threshold of multiple of the median determined by ROC curve. Screening values of genetic ultrasound were then evaluated by adding NB measurement to maternal age and NT measurement.

RESULTS

Two thousand and forty-four patients were included. We indexed 30 cases of T 21, 14 cases of Trisomy 18, 10 cases of Trisomy 13 and 25 cases of other karyotype abnormalities. Feasibility of measurement was 62% of all cases. We observed a significant relation between NB and NT (p = 0.001 ), as well as between NB and crown-rump-length (p < 0.0001 ). However, size of NB was not correlated to maternal ethnic group (p = 0.314). At 0.6 multiple of the median thresholds, screening values of NB measurement in T 21 were: sensibility 32%, false positive rate 10%, positive predictive value 13.6%, and negative predictive value 96.9%. The likelihood ratio for T 21 in case of NB < or = 0.6 multiple of the median was 4.4 (2.0-9.4). Screening values for maternal age and NT measurement were: sensitivity 88%, false positive rate 23%,positive predictive value 9.7%, and negative predictive value 99.6%. Inclusion of NB measurement increased sensitivity to 100%, positive predictive value to 13.6%, and negative predictive value to 100%, and decreased false positive rate to 5%.

CONCLUSION

NB measurement seemed to be a great sonographic marker for T 21. However, its low feasibility made it inadequate for routine settings in first trimester T 21 screening in an unselected population. Statistical independence with NT thickness needed to be further evaluated.

The relation between fetal nasal bone length and biparietal diameter in the Korean population

OBJECTIVE

To evaluate the relation between fetal nasal bone length (NBL) and biparietal diameter (BPD) at 15-19.9 (20) weeks of gestation by ultrasonography in the Korean population.

METHODS

The study population included 1268 Korean women (aged between 19 and 45 years) with a singleton pregnancy who registered at the Maternal Fetal Medicine Unit of Samsung Cheil Hospital between September 2003 and February 2005. Ultrasound measurements of NBL were performed using a strict sagittal plan of the fetal head. Other fetal biometry profiles were conducted before amniocentesis for fetal karyotyping.

RESULTS

NBL and fetal biometry profiles were measured successfully in 77.9% (988/1268) of the fetuses. NBL was found to increase linearly as a function of BPD (P < 0.001) with a median NBL of 4.4 mm (range 1.9-7.9). NBL increases through 15-19.9 (20) weeks of gestation were given by the equation NBL (mm) = 0.0836 x BPD (mm) + 1.368 (R2 = 0.1, P < 0.001).

CONCLUSIONS

Fetal NBL and BPD are linearly related in the second trimester. Fetal NBL in the Korean population is likely to be shorter than that reported for Caucasians and African-Americans.

Nasal bone in first-trimester screening for trisomy 21

OBJECTIVE

This study was undertaken to investigate the impact of incorporating assessment of the nasal bone into first-trimester combined screening by fetal nuchal translucency (NT) thickness and maternal serum biochemistry.

STUDY DESIGN

In this prospective combined screening study for trisomy 21, the fetal nasal bone was also examined and classified as present or absent. A multivariate approach was used to calculate patient-specific risks for trisomy 21 and the detection rate (DR) and false-positive rate (FPR) were estimated. We examined 2 screening strategies; first, integrated first-trimester screening in all patients and second, first-stage screening of all patients using fetal NT and maternal serum free beta-hCG and PAPP-A, followed by second-stage assessment of nasal bone only in those with an intermediate risk of 1 in 101 to 1 in 1000 after the first-stage.

RESULTS

The nasal bone was absent in 113 (0.6%) of the 20,165 chromosomally or phenotypically normal fetuses and in 87 (62.1%) of the 140 fetuses with trisomy 21. With combined first-trimester NT and serum screening, the DR of 90% was achieved at a FPR of 5%. Inclusion of the nasal bone, either in all cases or in about 10% of the total in the 2-stage approach, halved the FPR to 2.5%.

CONCLUSION

Inclusion of the nasal bone in first-trimester combined screening for trisomy 21 achieves a DR of 90% for a FPR of 2.5%.

Evaluating the efficiency of using second-trimester nasal bone hypoplasia as a single or a combined marker for fetal aneuploidy

OBJECTIVE

Although second-trimester nasal bone (NB) hypoplasia has been associated with fetal aneuploidy, its role as a single marker is still uncertain. Our objective was to evaluate the efficiency of NB hypoplasia as an independent marker for fetal aneuploidy.

METHODS

This was a prospective cohort study of women undergoing an anatomic survey between 16 and 22 weeks' gestation. The fetal NB and other markers of fetal aneuploidy, including nuchal fold, femur and humeral lengths, choroid plexus cysts, major fetal anomalies, echogenic bowel, pyelectasis, and hypoplastic fifth digits, were evaluated. Nasal bone hypoplasia was defined either as an absent NB or by a ratio of the biparietal diameter to NB. Fetuses or infants with fetal aneuploidy were compared with those without for the presence of NB hypoplasia either as a single marker or in the presence of other markers for aneuploidy.

RESULTS

Of 2885 women evaluated, NB measurements were obtained in 2465 (85%). There were 35 (1.4%) cases with fetal aneuploidy. The sensitivity and specificity of a single NB in detecting Down syndrome varied from 23% to 64% and 57% to 99%, respectively, depending on the definition of NB hypoplasia used. There was an improvement in the efficiency of using the NB when combined with other markers, with sensitivity and specificity increasing from 59% to 82% and 74% to 87%, respectively.

CONCLUSIONS

Nasal bone hypoplasia is a marker for fetal aneuploidy. The combination of the NB with other makers was associated with an improvement in detection of fetal aneuploidy.

First-trimester nuchal translucency, nasal bones, and trisomy 21 in selected and unselected populations

OBJECTIVE

The purpose of this study was to assess the role of fetal nasal bones evaluation in first-trimester screening for trisomy 21 in selected and unselected pregnancies.

STUDY DESIGN

Visualization of the nasal bones was attempted in women attending for routine nuchal translucency screening (unselected population, n = 7116, 12 cases of trisomy 21), as well as in high-risk pregnancies referred to our tertiary care center (selected population, n = 510, 23 cases of trisomy 21).

RESULTS

The sensitivity, specificity, positive and negative predictive value of absent nasal bones for trisomy 21 were 16.7%, 97.3%, 1.1%, 99.8% and 47.6%, 95.3%, 33.3%, 97.4% in the unselected and selected population, respectively. At logistic regression analysis including nuchal translucency and nasal bones findings, the latter resulted to be an independent predictor of trisomy 21 in the selected but not in the unselected population.

CONCLUSION

First-trimester nasal bones assessment for trisomy 21 screening has a very different performance in selected and unselected pregnancies.