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

Single nucleotide polymorphism array (SNP-array) analysis for fetuses with abnormal nasal bone

PURPOSE

This study aims to evaluate the prevalence of submicroscopic chromosomal abnormalities found on single nucleotide polymorphism array (SNP array) in pregnancies with either an absent or hypoplastic nasal bone.

METHODS

This retrospective study included 333 fetuses with either nasal bone hypoplasia or absence identified on prenatal ultrasound. SNP array analysis and conventional karyotyping were performed in all the subjects. The prevalence of chromosomal abnormalities was adjusted for maternal age and other ultrasound findings. Fetuses with either an isolated nasal bone absence or hypoplasia, those that had additional soft ultrasound markers, and those where structural defects were found on ultrasound were divided into three groups: A, B, and C, respectively.

RESULTS

Among the total cohort of 333 fetuses, 76 (22.8%) had chromosomal abnormalities, including 47 cases of trisomy 21, 4 cases of trisomy 18, 5 cases of sex chromosome aneuploidy, and 20 cases of copy number variations of which 12 were pathogenic or likely pathogenic. The prevalence of chromosomal abnormalities in group A (n = 164), B (n = 79), and C (n = 90) was 8.5%, 29.1% and 43.3%, respectively. The incremental yields by SNP-array compared with karyotyping in group A, B, and C were 3.0%, 2.5% and 10.7%, respectively (p > 0.05). Compared to karyotype analysis, SNP array detected an additional 2 (1.2%), 1 (1.3%), and 5 (5.6%) pathogenic or likely pathogenic CNVs in groups A, B, and C, respectively. In the 333 fetuses, the prevalence of chromosomal abnormalities in women with advanced maternal age (AMA) was significantly higher than that in non-AMA women, (47.8% vs. 16.5%, p < 0.05).

CONCLUSION

In addition to Down's syndrome, many other chromosomal abnormalities are present in fetuses with abnormal nasal bone. SNP array can improve the prevalence of chromosomal abnormalities associated with nasal bone abnormalities, especially in pregnancies with non-isolated nasal bone abnormalities and advanced maternal age.

Comparison of the ratio of second trimester fetal biometric measurements to fetal nasal bone length in fetuses with normal karyotype and trisomy 21

AIM

In this study, we compared the ratio of second trimester fetal biometric measurements to nasal bone length (NBL) in fetuses with normal karyotype and trisomy 21 to determine their diagnostic prognostic value.

MATERIALS AND METHODS

The study included 148 pregnant women who obtained second-trimester ultrasonographic fetal anatomy and had amniocentesis (AS) for fetal karyotyping. The fetal karyotype results divided the groups into normal and trisomy 21 fetuses. Age, obstetric history, first and/or second trimester screening test risk ratios, fetal biometric measurements, and NBL mm, median (MoM) multiples, and percentile values were recorded and compared between groups.

RESULTS

BPD/NBL ratios above 9.26 predict trisomy 21 in fetuses with 77.6% sensitivity and 86.1% specificity (p = 0.001). HC/NBL ratios above 34.50 predict trisomy 21 in fetuses with 77.8% sensitivity and 88.8% specificity (p = 0.001). FL/NBL ratios above 6.02 predict trisomy 21 in fetuses with 69.6% sensitivity and 72.2% specificity (p = 0.001). HL/NB ratios above 6.56 predict trisomy 21 in fetuses with 95.5% sensitivity and 47.2% specificity (p = 0.001). The NBL MoM value demonstrated a high diagnostic accuracy for normal-karyotype fetuses (p = 0.021).

CONCLUSION

We found that BPD/NBL, HC/NBL, FL/NBL, and HL/NBL ratios differed between fetuses with a normal karyotype and those with trisomy 21, specifically the HC/NBL ratio, which predicted trisomy 21 with good diagnostic accuracy. In identifying normal-karyotype fetuses, the NBL MoM was highly accurate.

Nasal bone in fetal aneuploidy risk assessment: are they independent markers in the first and second trimesters?

OBJECTIVES

In the mid-trimester ultrasound, nasal bone (NB) length can be used to correct the a priori risk for trisomy 21. Our study aims to evaluate if there is a correlation between an absent NB in the first trimester and a hypoplastic NB in the second trimester.

METHODS

Our two year retrospective analysis of data derived from routine clinical practice. Single euploid fetuses were included. The NB was assessed in both trimesters according to international guidelines and transformed into categorical variables. Logistic regression was performed in order to accomplish our main objective.

RESULTS

From the 759 normal pregnancies included, 45 (5.93%) had abnormal NB in the first trimester and 23 (3%) in the second trimester. Eleven cases (47.8%) of the abnormal NB in the second trimester were abnormal in the 11-14 weeks scan. After the diagnosis of an absent NB in the first trimester the odds ratio (OR) for a hypoplastic NB in the second trimester is 18.926 (7.791-45.977; p-value <0.01).

CONCLUSIONS

Our data suggest a strong association between the NB in the first and in the second trimester in normal euploid fetuses. This is important information to consider when counseling patients on the basis of this ultrasound marker.

Chromosomal Microarray Analysis for the Prenatal Diagnosis in Fetuses with Nasal Bone Hypoplasia: A Retrospective Cohort Study

Background

Previous studies have shown a strong correlation between fetal nasal bone hypoplasia and chromosomal anomaly; however, there is little knowledge on the associations of fetal nasal bone hypoplasia with chromosomal microdeletions and microduplications until now. Chromosomal microarray analysis (CMA) is a high-resolution molecular genetic tool that is effective to detect submicroscopic anomalies including chromosomal microdeletions and microduplications that cannot be detected by karyotyping. This study aimed to examine the performance of CMA for the prenatal diagnosis of nasal bone hypoplasia in the second and third trimesters.

Subjects and Methods

A total of 84 pregnant women in the second and third trimesters with fetal nasal bone hypoplasia, as revealed by ultrasound examinations, were enrolled, and all women underwent karyotyping and CMA with the Affymetrix CytoScan 750K GeneChip Platform. The subjects included 32 cases with fetal nasal bone hypoplasia alone and 52 cases with fetal nasal bone hypoplasia combined with other ultrasound abnormalities, and the prevalence of genomic abnormality was compared between these two groups.

Results

Karyotyping detected 21 cases of chromosomal anomaly in the 84 study subjects (21/84, 25%), including trisomy 21 (14 cases), trisomy 18 (3 cases), 46, del (4)(p16) karyotype (2 cases), 47, XYY syndrome (1 case) and 46, XY, del (5) (p15) karyotype (1 case). CMA detected additional four fetuses with pathogenic copy number variations (CNVs) and six fetuses with uncertain clinical significance (VOUS). No significant difference was detected in the prevalence of genomic abnormality in fetuses with nasal bone hypoplasia alone and in combination with other ultrasound abnormalities (13/32 vs 18/52; χ² = 0.31, P > 0.05). The pregnancy was terminated in 21 fetuses detected with chromosomal abnormality and 4 fetuses detected with pathogenic CNVs. Among the other six fetuses detected with VOUS, the parents chose to continue the pregnancy, and the newborns all had normal clinical phenotypes.

Conclusion

In addition to chromosomal abnormalities identified in 21 fetuses by karyotyping, CMA detected additional 10 fetuses with abnormal CNVs (10/84, 11.9%) in the study population. CMA is a promising powerful tool for prenatal diagnosis that may provide valuable data for the accurate assessment of fetal prognosis and the decision of pregnancy continuation during the prenatal clinical counseling.

Absent fetal nasal bone in the second trimester and risk of abnormal karyotype in a prescreened population of Chinese women

INTRODUCTION

The aim of this study was to evaluate the value of absent fetal nasal bone in the prediction of fetal chromosomal abnormalities, according to whether it was associated with other soft markers or structural abnormalities in a prescreened population of Chinese pregnant women.

MATERIAL AND METHODS

In this retrospective cohort study, women whose fetuses had absent nasal bone detected during the second trimester ultrasound scan were followed. Fetal karyotyping was performed and pregnancy outcomes were recorded. The association between absent fetal nasal bone with abnormal karyotype was evaluated according to whether soft markers or structural abnormalities were also observed.

RESULTS

Fetal nasal bone was assessed in 56 707 singleton pregnancies. After exclusion of unqualified cases, 71 (71/56 707, 0.13%) fetuses were included in the final analyses, of which 16 (16/71, 22.54%) were detected to have chromosomal abnormalities, including 12 cases of trisomy-21, three of trisomy-18, and one of micro-deletion (in 7q). Among the 42 cases with isolated absence of nasal bone, two had trisomy-21 and one had a micro-deletion. Absence of nasal bone in association with other structural abnormalities had a higher rate of abnormal karyotypes compared with isolated absence of nasal bone [83.33% (10/12) vs. 7.14% (3/42), Fisher's exact test χ²  = 25.620, p < 0.001].

CONCLUSION

Absent fetal nasal bone is a highly specific ultrasonographic soft marker that should be included in the routine second trimester ultrasound scan.

Screening performance of different methods defining fetal nasal bone hypoplasia as a single and combined marker for the detection of trisomy 21 in the second trimester

OBJECTIVE

To evaluate different methods of defining fetal nasal bone hypoplasia in the second trimester for the detection of trisomy 21.

METHODS

Prospective study in Greek women undergoing anomaly scan between 18 + 0 and 23 + 6 weeks. The following methods of defining nasal bone hypoplasia were evaluated, either as a single marker or in combination with others: (1) BPD to nasal bone length (NBL) ratio; (2) multiples of the median (MoM) of NBL, according to normal curves from a Greek population; (3-4) NBL < 2.5 percentile according to normal curves (3) commonly used internationally curves and (4) curves from a Greek population.

RESULTS

In total, 1301 singleton fetuses were evaluated - 10 with trisomy 21. The best detection rate of trisomy 21 was achieved when the applied method was nasal bone percentiles adjusted to maternal ethnicity, in combination with other markers (<2.5 percentile according to normal curves from a Greek population; p < 0.001; sensitivity 50%; specificity 94.8%; false-positive rate 5.2%; positive likelihood ratio 9.6).

CONCLUSION

Screening performance of fetal nasal bone hypoplasia in detecting trisomy 21 varies according to the method applied. The best screening performance is achieved by using percentiles adjusted to maternal ethnicity in combination with other markers of aneuploidy.

Systematic review and meta-analysis of performance of second-trimester nasal bone assessment in detection of fetuses with Down syndrome

OBJECTIVE

To review systematically the literature on diagnostic tests and performance of second-trimester sonographic assessment of nasal bone (NB) in identifying fetuses affected by Down syndrome.

METHODS

A search of studies involving screening tests for NB evaluation and measurements was carried out in the main international bibliographic databases (MEDLINE, EMBASE and CINAHL). Those considered to be relevant were then subjected to critical reading, following Critical Appraisal Skills Programme (CASP) criteria, by at least three independent observers. All data were extracted and tabulated by two independent investigators. A statistical synthesis of sensitivity, specificity and likelihood ratios was performed using specific software (Meta-DiSc).

RESULTS

From an initial list of 852 articles referring to ultrasound markers for Down syndrome, 207 relevant papers were selected. Following exclusions, 21 studies were included in the quantitative synthesis. The pooled estimates of positive and negative likelihood ratios were 40.08 (95% CI, 18.10-88.76) and 0.71 (95% CI, 0.64-0.79), respectively, for absent NB and 15.15 (95% CI, 8.15-28.16) and 0.47 (95% CI, 0.34-0.64), respectively, for hypoplastic NB. No relevant differences were found between the various means of defining nasal hypoplasia (multiples of the median (MoM) or percentiles). The biparietal diameter/nasal bone length (BPD/NBL) ratio showed somewhat higher sensitivity but lower specificity with a threshold effect.

CONCLUSIONS

NB absence or hypoplasia show high specificity and low but acceptable sensitivity in identifying fetuses with Down syndrome. Screening performance is better with NB measurements as a function of MoM or percentiles rather than as the BPD/NBL ratio. Classification of women into various risk groups for Down syndrome does not affect diagnostic performance.

PT/NBL ratio assessment at mid-trimester in prenatal screening for Down syndrome in a Chinese population

OBJECTIVE

To investigate the ratio of prenasal thickness (PT) to nasal bone length (NBL) in normal and trisomy 21 fetuses in the second and third trimester in Chinese population.

METHODS

The NBL and PT were measured blindly by using 3D volumes in 143 normal fetuses and 31 trisomy 21 fetuses.

RESULTS

The mean PT (r = 0.83, p = 0.004) and NBL (r = 0.87, p = 0.0062) both increased with the gestation age, while the PT/NBL ratio (r = 0.12, p > 0.10) remained stable. There was significant difference between normal and trisomy 21 fetuses (p < 0.001). If we took the 95th of the normal fetuses as the cut-off value, the detection rate was only 46%. By using ROC curve to evaluate the screening value of PT/NBL ratio, the area under receiver operating characteristic (ROC) curve was 0.88 (95% confidence interval 0.81 to 0.94, p < 0.0001).

CONCLUSIONS

In Chinese population, the PT/NBL ratio is not a very strong ultrasound marker to predict trisomy 21 fetuses. However, it can be used as an ultrasound marker for Down syndrome screening during the second and third trimester of pregnancy.

Three-dimensional ultrasonography measurement of fetal nasal bone length during the midtrimester in Taiwanese women

OBJECTIVE

To evaluate the normal range of the fetal nasal bone length (NBL) in Taiwanese women using three-dimensional (3D) ultrasound, and compare the NBL of normal fetuses with Down syndrome to determine its significance in screening for trisomy 21.

MATERIALS AND METHODS

A total of 102 consecutive fetuses and another 7 fetuses with trisomy 21, determined by karyotyping at 15-22 weeks' gestation, were evaluated with 3D ultrasound before amniocentesis at Changhua Christian Hospital between November 2003 and April 2004.

RESULTS

The normal range for NBL in the second trimester in the Taiwanese population was investigated, and a linear relationship with gestational age was noted. The NBL increased with advancing gestational age (NBL in cm=0.0264×gestational age in weeks -0.042 (R(2)=0.2416). The median of the biparietal diameter/nasal bone length ratio had a stable value which tended to change minimally between 15 and 22 weeks of gestation. Chromosomally normal fetuses had statistically longer nasal bones than fetuses with Down syndrome (p=0.014).

CONCLUSION

We present a reference range for 3D ultrasound measurement of the fetal NBL. A short nasal bone at 15 to 22 weeks is associated with a high risk of trisomy 21.

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.

Statistical analysis and interpretation of prenatal diagnostic imaging studies, Part 1: evaluating the efficiency of screening and diagnostic tests

Screening and diagnostic testing play fundamental roles in all fields of clinical medicine, with obstetric imaging and prenatal diagnosis being no exceptions. With advances in maternal serum screening and ultrasound technology, much research effort in the field of pre-natal diagnosis has actually been dedicated to the development and refinement of screening tests for fetal aneuploidy and other congenital disorders. This article aims to review the differences between screening and diagnostic tests, describe the accepted criteria for an efficient screening test, and provide an overview of the calculation and interpretation of test performance characteristics in relation to prenatal imaging studies.

Isolated absent or hypoplastic nasal bone in the second trimester fetus: is amniocentesis necessary?

OBJECTIVE

To elucidate the significance of isolated absent or hypoplastic nasal bone in the second trimester ultrasound scan.

METHODS

All cases of absent or hypoplastic nasal bone (length < 5th percentile) encountered during 2007-2009 were retrieved from database and all the ultrasound findings including structural abnormalities and soft markers for Down syndrome and fetal karyotype were reviewed. The cases were categorized into a study group with isolated absent or hypoplastic nasal bone and a comparison group with additional ultrasound findings. The incidence of Down syndrome confirmed by karyotyping was compared between the two groups.

RESULTS

Among 14 fetuses with absent or hypoplastic nasal bone identified, six (42.9%) had Down syndrome and eight (57.1%) were normal. All (100%) of the six fetuses with isolated absent or hypoplastic nasal bone (Study Group) had normal karyotype, while six (75%) of the other eight fetuses with additional ultrasound findings (Comparison Group) had Down syndrome (p = 0.010).

CONCLUSIONS

The use of isolated absent or hypoplastic nasal bone in the second trimester ultrasound scan for Down syndrome screening may not be effective. Amniocentesis, however, is indicated for fetuses with structural abnormality or additional soft marker which should be carefully searched by an experienced ultrasonographer.

Assessment of the ductus venosus, tricuspid blood flow and the nasal bone in second-trimester screening for trisomy 21

OBJECTIVE

To examine the prevalence of reversed a-wave in the ductus venosus, tricuspid regurgitation and absent nasal bone, in a second-trimester population undergoing amniocentesis, after exclusion of major fetal defects and to estimate the performance in screening for trisomy 21 based on maternal age and these markers in a general population.

METHODS

This was a retrospective study involving pregnancies undergoing amniocentesis due to increased risk for trisomy 21, mainly because of advanced maternal age. Before the invasive procedure, an ultrasound examination was carried out to exclude major fetal defects and to examine the ductus venosus, tricuspid blood flow and the presence of the fetal nasal bone. Modeling techniques were used based on 20 000 euploid pregnancies and 20 000 pregnancies with trisomy 21 to assess the screening performance in a general population.

RESULTS

The study population consisted of 3613 euploid pregnancies and 35 cases with trisomy 21. In the euploid group, reversed flow in the ductus venosus, tricuspid regurgitation and an absent nasal bone was observed in 1.7%, 1.5% and 0.1% of cases, respectively. In the trisomic group, these markers were found in 14.3%, 11.4% and 14.3% of cases, respectively. For a 5% false-positive rate, the detection rate in screening for trisomy 21, based on maternal age and either ductus venosus, tricuspid blood flow or nasal bone would be 33.8%, 32.4% or 31.4%, respectively. Screening by maternal age alone would detect 29.0% of the fetuses with trisomy 21. Receiver-operating characteristics curve analysis showed a slight but significant improvement in screening performance for trisomy 21 based on the inclusion of these markers.

CONCLUSION

Second-trimester ultrasound screening for trisomy 21 based on maternal age with additional assessment of the ductus venosus, tricuspid blood flow and the fetal nasal bone in otherwise normal-appearing fetuses is only marginally better than is screening by maternal age alone.

The genetic sonogram: comparing the use of likelihood ratios versus logistic regression coefficients for Down syndrome screening

OBJECTIVES

The purpose of this study was to compare the screening efficiency for Down syndrome using likelihood ratios versus logistic regression coefficients.

METHODS

We conducted a retrospective study of women at increased risk for Down syndrome referred for a second-trimester genetic sonogram. Likelihood ratios were calculated by multiplying the risk ratio from maternal serum screening by the likelihood ratios of sonographic markers. Logistic regression coefficients were calculated using a formula derived from β coefficients generated from a multivariable logistic regression model. The screening efficiency of both methods was tested in an independent population of patients. The McNemar test was used to compare the predictive ability of the two methods.

RESULTS

In the validation population, the use of likelihood ratios had an area under the receiver operator characteristic curve of 0.90 for Down syndrome detection, whereas the use of logistic regression coefficients had an area under the curve of 0.86. Adopting a risk cutoff point of 1/270, the sensitivity of likelihood ratios was 77.4% (95% confidence interval [CI], 58.9%-90.4%) with a false-positive rate of 17.9% (95% CI, 15.0%-21.1%), whereas the sensitivity of logistic regression coefficients was 93.5% (95% CI, 78.6%-99.2%) with a false-positive rate of 34.6% (95% CI, 30.9%-38.4%). There was significant difference in screening efficiency for Down syndrome detection between the two methods (exact McNemar χ(2), P < .001 ).

CONCLUSIONS

With a slight reduction in the Down syndrome detection rate, the use of the likelihood ratio approach was associated with a significantly lower false-positive rate compared with the logistic regression approach.

Normative curves of fetal nasal bone length for the ethnic Chinese population

OBJECTIVE

The purpose of this study is to determine the association between fetal nasal bone length (NBL) and gestational age (GA), biparietal diameter (BPD) and head circumference (HC) in women undergoing prenatal assessments and Down syndrome screening.

METHODS

Cross-sectional data were obtained from 3,003 women with singleton pregnancies who underwent a prenatal ultrasound examination at the Department of Obstetrics and Gynecology, Cheng Hsin General Hospital between August 2006 and July 2009.

RESULTS

Statistical analyses involved linear regression. NBL with GA, BPD and HC as measured between 14(+0) and 35(+6) weeks of gestation were linearly related.

CONCLUSIONS

Using multiple parameters (GA, BPD and HC) to estimate NBL is more accurate than using than using GA or BPD or HC alone, as indicated by the higher predictive value.

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

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

Comparison of the efficiency of second-trimester nasal bone hypoplasia and increased nuchal fold in Down syndrome screening

OBJECTIVE

The purpose of this study was to compare the efficiency of second-trimester nasal bone hypoplasia (NB) and increased nuchal fold (NF) in Down syndrome screening.

STUDY DESIGN

This was a prospective multicenter cohort study of women who underwent an anatomic survey between 16 and 22 weeks of gestation. The fetal NB and other markers of fetal aneuploidy that included NF were evaluated. NB was defined either as an absent NB or length of <0.75 multiples of the median for the gestational age. Two definitions of increased NF (>5 mm and >6 mm) were evaluated. Fetuses or infants with Down syndrome were compared with those fetuses without for the presence of NB and increased NF.

RESULTS

Among 4373 pregnancies that were evaluated over a 5-year period, there were 50 pregnancies with Down syndrome. NB evaluation was obtained in 3936 of 4373 pregnancies (90%); NF was evaluated in all of the fetuses. Absent NB was seen in 14/49 cases (29%), and NF of >6 mm was seen in 6 of 50 cases (12%) with Down syndrome.

CONCLUSION

Nasal bone and nuchal fold are efficient markers for Down syndrome. Absent nasal bone was a better predictor of Down syndrome, compared with nuchal fold, and should be a standard marker when a second-trimester genetic sonogram is performed.

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.

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.

Fetuses with Down syndrome have an enlarged anterior fontanelle in the second trimester of pregnancy

OBJECTIVE

Neonates with Down syndrome are known to have an enlarged anterior fontanelle. The aim of this study was to assess whether fetuses diagnosed with Down syndrome in the second trimester have larger anterior fontanelles in comparison with normal euploid fetuses.

METHODS

The study population included 13 fetuses with trisomy 21 and 26 normal euploid fetuses analyzed between the 19(th) and the 23(rd) weeks of gestation. The anterior fontanelle was assessed by three-dimensional ultrasound, with the midsagittal plane of the fetal head being the reference view for acquisition of the volume. Anteroposterior and laterolateral diameters, perimeter and area of the fontanelle were then measured offline; the diameters were normalized for biparietal diameter and the perimeter and area were normalized for head circumference. Non-parametric statistical analysis was used to compare the mean values of all variables in the two groups of fetuses. Intra- and interobserver variability were also assessed.

RESULTS

All variables except the fontanelle laterolateral diameter were significantly greater in Down syndrome fetuses than in controls, with anterior fontanelle perimeter/head circumference and fontanelle area/head circumference ratios showing the highest sensitivity for the detection of Down syndrome. Using a cut-off of 2.1 for the fontanelle area/head circumference ratio, the sensitivity and specificity for the detection of Down syndrome were 77% and 96%, respectively.

CONCLUSION

During the mid-trimester the dimensions of the anterior fontanelle are significantly increased in fetuses with Down syndrome in comparison with normal euploid fetuses. This finding may be of help in the detection of trisomy 21 at the time of the anomaly scan.

Defining nasal bone hypoplasia in second-trimester Down syndrome screening: does the use of multiples of the median improve screening efficacy?

OBJECTIVE

The purpose of this study was to compare the efficacy of the use of nasal bone (NB) multiples of the median (MoM) with the biparietal diameter (BPD)/NB ratio as definitions of NB hypoplasia that is associated with Down syndrome in the second trimester.

STUDY DESIGN

We conducted a prospective cohort study of women who underwent an anatomic survey between 16 and 22 weeks of gestation. The fetal NB and other markers of fetal aneuploidy were evaluated. MoMs for the NB length at each gestational age category were calculated and adjusted for maternal race. NB hypoplasia was defined either as an absent NB or by a ratio of the BPD/NB >11 or by NB lengths <0.75, 0.5, and 0.25 MoM for the gestational age, respectively. Fetuses or infants with Down syndrome were compared with those without for the presence of NB hypoplasia.

RESULTS

Among 3634 women whose condition was evaluated, NB assessment was obtained in 3197 women (88%). There were 23 cases of Down syndrome that were detected. Receiver operating characteristic curve comparison revealed NB MoM <0.75 to be the best definition of NB hypoplasia (area under receiver operating characteristic curve, 0.75). NB <0.75 MoM had a sensitivity and specificity of 49% (95% CI, 26-69) and 92% (95% CI, 91%-93%), respectively, compared with 61% (95% CI, 38%-80%) and 84% (95% CI, 82%-85%), respectively for BPD/NB >11. The difference in the sensitivity of 12% (95% CI, -5-31) with the BPD/NB ratio >11 vs with an NB MoM <0.75 was not significant (P < .25). The difference in the specificity of 8% (95% CI, 7.5-9.5) with the BPD/NB ratio >11 vs an NB MoM <0.75 was significant (P < .0001).

CONCLUSION

In the second trimester of pregnancy, the use of nasal bone length <0.75 MoM for the gestational age was the best definition for Down syndrome detection and resulted in improved specificity.

Absent or shortened nasal bone length and the detection of Down Syndrome in second-trimester fetuses

OBJECTIVE

To estimate the accuracy of evaluating nasal bone length, expressed as multiples of the median (MoM), for the detection of Down syndrome in second- trimester fetuses.

METHODS

Expected normal median nasal bone measurements were established for an initial cohort of women receiving fetal ultrasound examinations at 15-24 weeks of gestation. Nasal bone lengths were converted to MoM with adjustment for maternal race and ethnicity using whites as the referent group. Nasal bone MoM were compared in euploid and Down syndrome fetuses. The sensitivity and specificity were evaluated in this initial cohort and in a second cohort in which all ultrasound measurements were carried out prospectively.

RESULTS

For the combined data set, 10 of 21 affected pregnancies had an absence of the nasal bone (sensitivity 47.6%), but absence was noted in only 1 of 2,515 unaffected pregnancies (false-positive rate 0.04%). Using less than 0.80 MoM as a cutoff, the sensitivity was 20 of 21 (95.2%), and the false-positive rate was 185 of 2,515 (7.4%). Changing the cutoff to 0.75 MoM resulted in 18 of 21 (85.7%) sensitivity and 74 of 2,515 (2.9%) false-positive rate. Using medians derived from whites to calculate MoM for the entire population resulted in higher false-positive rates.

CONCLUSION

Nasal bone length expressed as MoM seems to be an useful ultrasound marker for Down syndrome in second-trimester fetuses with a high sensitivity and a low false-positive rate.

LEVEL OF EVIDENCE

III.