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

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.

Role of Sonographic Second Trimester Soft Markers in the Era of Cell-Free DNA Screening Options: A Review

Soft markers are sonographic structural, nonspecific signs with little pathological significance, often transient, usually considered as normal variants. However, they may also be associated with chromosomal abnormalities. The most widely examined soft markers include absent or hypoplastic nasal bone (NB), intracardiac echogenic focus (IEF), ventriculomegaly (VM), thickened nuchal fold (NF), choroid plexus cyst (CPC), echogenic bowel, short long bones, and urinary tract dilation (UTD). Although the use of noninvasive prenatal testing (NIPT) has been spreading quickly in maternal–fetal medicine, it is not a diagnostic test and it still remains unavailable or cost-prohibitive for most of the population in many countries. After normal screening test results in the first trimester, there is no uniform consensus regarding the clinical significance of isolated soft markers for aneuploidy. Nowadays, the search for soft markers in an ultrasound is still part of clinical evaluation, and the interpretation of these findings is often a matter of debate. In the present review, we summarize the recent literature about the role of soft markers in the era of NIPT and propose an overview of the different clinical guidelines.

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.

Isolated absence of nasal bone in 1 fetus in a dizygotic pregnancy after in vitro fertilization: A case report

RATIONALE

During ultrasound prenatal screening, absence of the fetal nasal bone is used as a marker for common aneuploidies in singleton pregnancies. However, its application in multiple pregnancies is less sensitive and more challenging owing to difficulties in obtaining adequate views of the fetal face.

PATIENT CONCERNS

A 38-year-old woman with dichorionic-diamniotic (DCDA) pregnancy and a history of in vitro fertilization and embryo transfer was referred to our hospital with the absence of the nasal bone noted on ultrasound images obtained during the second trimester in 1 fetus.

DIAGNOSIS

Prenatal sonographic examination revealed the absence of the nasal bone in 1 fetus in the DCDA gestation. Amniocentesis performed on the dual amniotic sacs revealed normal karyotypes for each twin. The absence of the nasal bone was confirmed on a radiograph obtained postnatally in 1 infant.

INTERVENTIONS

The mother underwent routine outpatient care according to the gestational age and successfully delivered following lower-segment cesarean section.

OUTCOMES

Two live infants were uneventfully delivered. Radiography confirmed the absence of the nasal bone in 1 of the newborns on postnatal day 3. The infants were followed up until 2 years and 9 months of age, which revealed normal appearance and eating and breathing functions.

LESSONS

Prenatal diagnosis of the absence of nasal bone in 1 fetus of DCDA pregnancy has rarely been reported. Although a fetus with the absence of the nasal bone in DCDA gestation poses a significant risk of aneuploidy, it is acceptable when the defect is an isolated anomaly after ruling out genetic abnormalities. Appropriate consultation should be provided for these patients.

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.

Fetal nasal bone hypoplasia in the second trimester: Comparison of diagnostic methods for predicting trisomy 21 (Down syndrome)

PURPOSE

The aim of this prospective observational study was to identify the best method for use in diagnosing fetal nasal bone (NB) hypoplasia in the second trimester as a means of predicting trisomy 21 (Down syndrome).

METHODS

The NB length (NBL), NBL percentiles, and NBL multiple-of-median (MoM) values and the biparietal diameter-to-NBL ratios were calculated and compared in an attempt to identify the best predictive method and most appropriate cutoff value. Predictive values for several cutoff points were calculated. Receiver operating characteristic curves at a fixed 5% false-positive rate were used to compare the four methods.

RESULTS

NBL measurements were obtained from 2,211 (95.6%) of a total of 2,314 fetuses. Data from 1,689 of those 2,211 fetuses were used to obtain reference ranges, derive a linear regression equation, and calculate NBL percentiles and MoM values. Using a fixed 5% false-positive rate, we found 25.5% sensitivity for NBL (95% confidence interval [CI], 15-39.1) and 23.5% sensitivity for NBL percentiles (95% CI, 13.4-37), NBL MoM values (95% CI, 13.4-37), and biparietal diameter-to-NBL ratios (95% CI, 13.4-37).

CONCLUSIONS

Our study demonstrated that all four methods can be used in the second trimester for diagnosing fetal NB hypoplasia as a means of predicting trisomy 21 because their predictive values are similar at a fixed 5% false-positive rate. For simplicity of use, we recommend using 3 mm as the NBL cutoff value.

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.

[News methods for second trimester screening of Down syndrome: statistical analysis of the use of nasal bone length and prenasal thickness]

INTRODUCTION

Sonographic measurements of nasal bone length and prenasal soft tissue thickness are ultrasonographic methods for prenatal screening of Down syndrome.

AIM

The aim of the authors was to create a local normogram for nasal bone length and prenasal soft tissue thickness measurements and to test the performance of different statistical methods.

METHOD

Euploid (N = 1500) and trisomy 21 foetuses (N = 10) studied between April 2008 and December 2013 were included. Nasal bone length and prenasal thickness measurements were performed at the Medisono Fetal and Maternal Health Research Centre, Szeged, and cytogenetic tests were performed at the Department of Medical Genetics, University of Szeged, Hungary. Normograms were created with different number of patients (N = 100, 300, 500, 750. 1000 and 1500) and using 3 different statistical methods (linear regression, square-based regression, and box-plot analysis).

RESULTS

The results indicated that at least 1000 measurements are strongly recommended for the normograms. The increase of patient number improved the efficacy of the normograms in each of the 3 statistical methods used for analysis. In general practice box-plots provides a better performance over the other screening methods. However, advanced level screening requires local linear normograms for the best screening results.

CONCLUSION

The use of box-plots is recommended for the use in the daily practice but regression-based normograms are necessary for advanced prenatal screening.

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.

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.

Nasal bone assessment in fetuses with trisomy 21 at 16-24 weeks of gestation by three-dimensional ultrasound

OBJECTIVE

This study aims to investigate the length and shape of the nasal bones in fetuses with trisomy 21 at 16-24 weeks' gestation.

METHOD

We acquired three-dimensional volumes of the fetal profile from 41 fetuses with trisomy 21. The multiplanar mode was used to measure nasal bone length in the exact midsagittal plane and in parasagittal and oblique views of the fetal face and to examine the nasal bones in the coronal plane.

RESULTS

There was bilateral absence of the nasal bones in 11 (26.8%) cases and unilateral absence in one (2.4%). In 29 (70.7%) cases with present nasal bones, there was progressive over-estimation of nasal bone length when measured in parasagittal and oblique views compared to measurements taken in the exact midsagittal plane. In the coronal plane, in 18 of 29 (62.1%) fetuses with trisomy 21, the nasal bones were divergent, whereas in 131 of 135 (97.0%) euploid fetuses, the bones were entirely fused in the midline.

CONCLUSION

Parasagittal and oblique scanning planes may produce over-estimation of nasal bone length in trisomy 21 fetuses because they often have divergent nasal bones. Consequently, it is essential that measurement of nasal bone length is carried out in the exact midsagittal plane of the face.

Three-dimensional ultrasound imaging and measurement of nasal bone length, prenasal thickness and frontomaxillary facial angle in normal second- and third-trimester fetuses

OBJECTIVES

To assess the feasibility of nasal bone length (NBL), prenasal thickness (PT) and frontomaxillary facial (FMF) angle measurements performed on the same three-dimensional (3D) multiplanar-corrected profile view in healthy second- and third-trimester fetuses, to create reference ranges and to review published measurement techniques.

METHODS

3D volumes of 219 healthy second- and third-trimester fetuses were retrospectively analyzed. The quality of images and measurability of the markers were assessed with 5-point and 3-point scoring systems, respectively. Measurements of NBL (with care to exclude the frontal bone), PT and FMF were obtained in the exact mid-sagittal plane. Reference ranges were constructed based on measurements from images with high-quality (4 or 5 points) and high measurability (2 or 3 points) scores and compared with those in the most relevant published literature.

RESULTS

A high-quality score was assigned to 111 images. Among these, a high measurability score was significantly more often achieved for NBL (98.2%) and PT (97.3%) than for the FMF angle (26.1%) (P < 0.001). Both NBL (NBL = - 6.927 + (0.83 × GA) - (0.01 × GA(2))) and PT (PT = (0.212 × GA) - 0.873) (where GA = gestational age) showed growth with gestation, with less pronounced growth for NBL after 28 weeks. Our reference range for the NBL showed a systematically smaller length than those in other two-dimensional (2D) ultrasound-based publications. The FMF angle measurements that we obtained did not show a significant change with GA.

CONCLUSIONS

NBL and PT are easily measured using 3D ultrasound whereas FMF angle measurement is more challenging. When it is measured in the exact mid-sagittal plane and care is taken to exclude the frontal bone, measurements of the NBL are systematically smaller than those in previous 2D ultrasound-based publications.

Normal ranges for fetal nasal bone length determined by ultrasound at 18-20 weeks of gestation in a multiethnic Australian population

OBJECTIVE

Absence or hypoplasia of the nasal bone is commonly reported in Down syndrome fetuses. We define normal ranges and the 2.5th centile for fetal nasal bone length (NBL) in a multiethnic Australian population at 18-20 weeks of gestation.

METHODS

A prospective cohort study of women attending for a routine anomaly scan. Ethnicity of the patient and their partner was recorded, and the nasal bone was measured three times. Two methods of nasal bone assessment were used to define normal ranges: a single (first) measurement and the mean value of three measurements. Mixed-effects regression models were employed to account for interoperator differences treating sonographers as random effects. Nonparametric methods were used to define the 2.5th centile for gestational age.

RESULTS

A total of 1199 women were included with a mean gestational age 19.1 (SD 0.4; range 18-20) weeks. There is significant linear relationship between NBL and gestational age (P<0.001). The mean of three nasal bone measurements had a smaller standard deviation than single nasal bone measurements. Nonparametric assessment was used to define the 2.5th centile, which is 4.4 mm at 18 weeks and 5.0 mm at 20 weeks of gestation.

CONCLUSIONS

This study provides a reference range for fetal NBL at 18-20 weeks of gestation in an unselected multiethnic Australian population. Whilst NBL increases linearly from 18 to 20 weeks, the data are not normally distributed and nonparametric techniques are required to define the 2.5th centile. The mixed-effects model also accounts for variation in sonographer measurements.

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.

First trimester ultrasound: current approaches and practical pitfalls

Revolutionary technological improvements and high-frequency transvaginal scanning have enabled the resolution of ultrasound imaging in the first trimester to increase such that detailed early fetal development can now be well visualized. This investment in imaging technology has enabled not only normal embryonic development but also chromosomal abnormalities and structural anomalies to be more easily and accurately diagnosed before the second trimester. This article is intended to help radiologists in the interpretation and clinical application of normal and abnormal first trimester ultrasound findings in early pregnancy. We review the current literature and applications and interpretations of first trimester ultrasound.

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.

Screening for fetal abnormalities with ultrasound

PURPOSE OF REVIEW

This review serves to explore literature published during the past year that has focussed on sonographic screening for fetal abnormalities.

RECENT FINDINGS

The evolving nature of screening for fetal aneuploidy has continued to feature strongly in recent literature. There is growing interest in early detailed ultrasound of fetal anatomy at the time of nuchal translucency thickness assessment. Demonstration of tricuspid regurgitation and ductus venosus assessment have been shown to be beneficial additional second-line tests for aneuploidy screening in high-risk patients. Frontomaxillary facial angle assessment has been explored as a new marker for aneuploidy. The limitations of first-trimester nasal bone measurement were reiterated while its measurement has been shown to be beneficial in the second trimester, especially when calculated with multiples of the median. As regards second-trimester screening, studies have explored the effectiveness of congenital heart-defect screening and the efficiency of the genetic sonogram for trisomy 21. The role of nuchal translucency discordance in monochorionic twins has also been readdressed.

SUMMARY

Screening for fetal abnormalities continues to evolve with the introduction of novel techniques and the further refinement of previously proposed screening tools. How these modalities are implemented into routine clinical practice remains to be seen.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.