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PubMed2005

Technical aspects of nuchal translucency measurement.

Nuchal translucency (NT) describes an echo-free area, below the skin, in the posterior nuchal and back region of the fetus and is typically observed in the first and early second trimester of pregnancy. A wide NT has been correlated with chromosomal and congenital abnormalities in the fetus. An accurate NT measurement is a critical component of the estimation of Down syndrome risk in the first trimester of pregnancy and the Nuchal Translucency Quality Review Program (NTQR) identified nine criteria that ensure an accurate measurement of NT during ultrasound examination. The purpose of this chapter is to present the technical aspects of obtaining an accurate NT measurement on ultrasound as outlined by the NTQR.

Chromosome Aberrations↗
PubMed2002

First-trimester trisomy screening: nuchal translucency measurement training and quality assurance to correct and unify technique.

OBJECTIVE: To describe the process of training for measuring nuchal translucency at five clinical centers in North America and to evaluate methods of quality assurance and feedback. DESIGN: Throughout a period of 18 months, the performance of sonographers in measuring fetal nuchal translucency was monitored using qualitative and quantitative methods of review. After 12 months, different approaches (written and personal feedback) were used to inform sonographers of technical aspects that needed to or could be improved. RESULTS: On initial qualitative review, discrepancies in judgment from different reviewers coincided with suboptimal magnification, failure to visualize the amniotic membrane and/or use of cross-shaped calipers. At subsequent global review, 13 (29%) images of nuchal translucency measurements were considered unacceptable. Quantitative assessment revealed that, during the first part of the study, the means from four sonographers were significantly smaller and the mean from the fifth sonographer was significantly larger than expected on the basis of findings from The Fetal Medicine Foundation (P < 0.0001). Following feedback, sonographers who underestimated nuchal translucency and who received a written report only did not change measurements overall (P = 0.9759). In contrast, those who received additional intervention showed a marked difference (P < 0.0001). CONCLUSIONS: Global qualitative review of images from one sonographer may be preferable to assessment of individual aspects of images. Results from global qualitative review correspond well with findings from quantitative analysis, indicating that the latter can be applied for ongoing audit. Observation of divergent results should prompt extensive personal feedback, rather than a written report, to prevent sonographers from settling in their own, inappropriate technique.

Allied Health Personnel↗
PubMed2000

First trimester ultrasound with nuchal translucency measurement for Down syndrome risk estimation using software developed by the Fetal Medicine Foundation, United Kingdom--the first 2000 examinations in Newcastle, New South Wales, Australia.

In September 1997 screening for Down syndrome using first trimester ultrasound to measure nuchal translucency, with risk estimation by the software program developed in the United Kingdom by the Fetal Medicine Foundation, was introduced in Newcastle, New South Wales. In the first 2,000 such risk estimations 134 women (6.7 %) were screen positive (with a risk of greater than 1 in 300 at that gestation for Trisomy 21). In the first 1,000 of these 2,000 fetuses delivered thus far there were 8 cases of Trisomy 21, 2 of Trisomy 18 and 1 of 47 XXX. Nine of these 11 were screen positive, the only false negative results being for 2 cases of Trisomy 21. The detection rate for Trisomy 21 was 6 out of 8 (75%) and for every case of Trisomy 21 (Down Syndrome) detected by this process, 11.3 invasive tests would have been needed to make that diagnosis in a screen positive woman.

Down Syndrome↗
PubMed1998

The effect of nuchal cord on nuchal translucency measurement at 10-14 weeks.

The aim of this study was to determine the incidence of nuchal cord and its possible effect on nuchal translucency thickness at 10-14 weeks' gestation. Out of 316 consecutive pregnancies in which nuchal translucency thickness was measured transabdominally, 26 (8.23%) fetuses were shown to have the umbilical cord around the neck. The umbilical cord can be measured together with the nuchal translucency thickness when it passes around the fetal neck and this adds a mean of 0.8 mm to the actual translucency measurement. After the thickness of the cord was subtracted, the measurements of nuchal translucency thickness did not differ from those in the overall population studied. Of the 22 fetuses available for follow-up, a nuchal cord was found in only one at 20 weeks and in none at delivery. Our findings indicate that the presence of a nuchal cord may bias the results of fetal nuchal translucency measurement and that the use of color Doppler might decrease the false-positive rate in screening for fetal aneuploidy by nuchal translucency measurement at 10-14 weeks' gestation.

Female↗
PubMed1995

Nuchal translucency measurement in normal fetuses.

OBJECTIVE: To construct a normal range for the nuchal translucency measurement in chromosomally and phenotypically normal fetuses between 9 and 14 weeks' gestation. METHODS: The nuchal translucency was measured prospectively in 771 chromosomally normal fetuses of women attending our antenatal clinic or prenatal diagnosis center. The nuchal translucency measurement was expressed as the median and fifth, 25th, 75th, and 95th percentiles according to completed weeks of gestation based on ultrasound measurements. RESULTS: The median nuchal translucency measurement increased from 0.7 mm at 10 weeks' gestation to 1.5 mm at 13 weeks. A nuchal translucency measurement greater than 2.5 mm was found in 4.6% of the fetuses at 10 weeks' gestation; the incidence increased to 8.7% at 14 weeks. CONCLUSION: In normal fetuses, there is a physiologic variation in the nuchal translucency measurement between 9 and 14 weeks' gestation. The calculation of risk for trisomies based on this measurement should take this variation into account. The adoption of a gestational age-dependent cutoff point, based on the deviation of a given measurement from the median, may reduce the number of false-positive test results requiring invasive procedures for karyotyping.

Adolescent↗
PubMed1996

Nuchal translucency measurement: training of potential examiners.

The aim of this study was to assess a training regimen for nuchal translucency measurement by transabdominal (TAS) and transvaginal sonography (TVS). After initial instruction regarding the criteria for correct nuchal translucency measurement, trainees (A and B) and an experienced examiner (C) performed nuchal translucency measurements on fetuses of 10-13 weeks' gestation, and the trainees' ability to obtain a measurement, repeatability and levels of agreement were assessed. In addition, a further experienced examiner (D) performed nuchal translucency measurements to validate the training regimen. Examiner C obtained nuchal translucency measurements in 94% by TAS, 93% by TVS and 100% by a combination of both scan modes. The repeatability coefficient was 0.40 mm and 0.24 mm for TAS and TVS, respectively. Trainees A and B were considered trained after 80 and 100 scans with TAS and TVS, respectively. They were considered trained when they could consistently obtain measurements that were of comparable repeatability and comparable levels of agreement with those of examiner C. The trainees' difficulties with TAS were in achieving satisfactory repeatability and levels of agreement, but with TVS it was ability in obtaining a measurement. We propose the training methods, standards and criteria used in this study as the basis for training sonographers in nuchal translucency measurements.

Chromosome Aberrations↗
PubMed2003

Ductus venosus assessment at the time of nuchal translucency measurement in the detection of fetal aneuploidy.

OBJECTIVE: To assess the potential value of ductus venosus Doppler studies in the detection of fetal aneuploidy on measurement of nuchal translucency. METHODS: The pulsatility index for veins (PIV) and the lowest velocity during atrial contraction (A-wave) were determined in the fetal ductus venosus in 3382 consecutive pregnancies at 10 to 14 weeks and studied from December 1996 to December 2001. Nuchal translucency was also measured. The population studied included 1664 pregnancies at high risk and 1718 at low risk for fetal aneuploidy. RESULTS: In relation to the prenatal detection of trisomy 21, the ductus venosus PIV was increased in 75% (36/48), the A-wave was decreased in 58% (28/48), and nuchal translucency was enlarged in 81% (39/48) of the trisomy 21 fetuses [71% (22/31) when nuchal translucency referrals were excluded]. The corresponding figures for trisomies 18 and 13 were 71, 58 and 83%, respectively, being 33, 33 and 33% for other unbalanced anomalies. CONCLUSION: There is a high proportion of fetuses with trisomies 21, 18 and 13 (around 75%) in which the ductus venosus PIV is increased (above the 95th percentile) at 10 to 14 weeks, this proportion being similar to that observed for increased nuchal translucency measurement.

Adolescent↗
PubMed2002

[Pregnancy outcome in 1,252 fetuses after nuchal translucency measurement in the 1st trimester].

The measurement of the nuchal translucency is an important marker to detect a vast number of fetal anomalies. Lately the nuchal translucency has been used increasingly as a screening method to find chromosomal anomalies especially for trisomy 21. Beside a high incidence of chromosomal defects one assumes a high risk of rare syndromes and other associated anomalies such as heart defects, skeletal anomalies, cerebral anomalies, diaphragmatic hernias, as well as of an intrauterine death. In view of abortion rate, detection rate of chromosomal anomalies, other fetal anomalies and rare syndromes we evaluated in this study the pregnancy outcome after nuchal translucency measurement, and discuss a concept for its management.

Chromosome Aberrations↗
PubMed2000

Intra- and interoperator repeatability of the nuchal translucency measurement.

OBJECTIVE: The aim of this study was to assess the repeatability of nuchal translucency measurement by well-trained sonographers either experienced or inexperienced with the measurement. METHODS: The nuchal translucency was measured three times by two out of nine operators in 161 pregnant women attending two teaching hospitals. Intra-operator and inter-operator variation was assessed by calculating the standard deviation (SD). Intraclass Correlation Coefficients (ICC) with a 95% lower confidence limit (95% CL) were calculated for each operator and for pairs of operators. Intra- and inter-operator kappa statistics were calculated, after dichotomising the results into a nuchal translucency smaller or larger than 3 mm. RESULTS: The SD of intra-operator difference was 0.35 mm. The intra-operator repeatability showed ICCs varying from 0.83 to 0.95 for the experienced operators and from 0.47 to 0.83 for the inexperienced. The SD of inter-operator differences was 0.56 mm, 0.46 mm and 0.44 mm, based on one, two and three measurements, respectively. The inter-operator repeatability showed a variation in ICC from 0.74 to 0.95 in pairs of experienced sonographers to 0.51 in one pair inexperienced with the measurement. The kappa value expressing the intra and inter-operator repeatability as being > 3 mm or < 3 mm was 0.88 and 0.85, respectively. CONCLUSION: This study supports the finding that the nuchal translucency measurement is reproducible, as long as it is performed by sonographers well trained in the technique of this measurement.

Down Syndrome↗
PubMed2004

[Nuchal translucency measurement--non invasive ultrasound screening for fetal abnormalities. Part I].

OBJECTIVE: Fetal abnormalities are the most common cause of perinatal and postnatal death and infant handicap. In the last years came into being many diagnostic methods making possible--precise and accurate diagnosis of fetal malformation. DESIGN: Estimation the value of the screening test for fetal abnormalities based on the nuchal translucency measurement between 10-14th week of pregnancy. MATERIAL AND METHODS: A group of 675 women with singleton pregnancies undergoing first trimester nuchal translucency measurement. Nuchal translucency thickness was measured by transvaginal ultrasound examination according to Nicolaides. Derived risks were then calculated. RESULTS: When we used a risk of 1:250 as the cutoff to define a positive result on the screening test, the rate of detection of fetal abnormalities was 100%, with a false positive rate of 1.3%. CONCLUSION: First trimester nuchal translucency measurement is an effective method of screening for fetal abnormalities (obstetrical high-risk group).

Adult↗
PubMed2001

First-trimester Down's syndrome screening by fetal nuchal translucency measurement in Taiwan.

BACKGROUND: Fetal nuchal translucency (NT) measurement is now widely used in many Western countries as a screening tool for Down's syndrome during the first trimester. However, at present there is no data on its use in Taiwan. The purpose of the present study was to evaluate the efficacy of NT measurement in first-trimester Down's syndrome screening in Taiwan. METHODS: We conducted a prospective study from October 1997 to May 1999. Sonographic measurement of fetal NT was performed in 1,249 fetuses at 9-14 weeks of gestation. Transabdominal ultrasound scanning was performed to obtain a sagittal section of the fetus for measuring the crown-rump length (CRL) and the maximum thickness of the subcutaneous translucency between the skin and the soft tissue overlying the cervical spine. Two different cut-off points were used for screening: a fixed cut-off point of at least 2.5 mm and a CRL-related cut-off point. In the latter method, fetuses with an NT measurement in the 95th percentile were considered at high risk for Down's syndrome. RESULTS: Three fetuses had Down's syndrome, with NT measurements of 2.1 mm, 2.7 mm, and 4.0 mm. The false positive rates for the fixed cut-off point and CRL-related cut-off point were 6.3% and 4.6%, respectively. Both methods had a sensitivity of 66.7%. However, the screening program using the CRL-related cut-off point had two advantages: a higher specificity (95.5% vs 93.8%) and a more reasonable distribution pattern for screening. CONCLUSION: This study showed that NT measurement is a potential screening tool for Down's syndrome during the first trimester in Taiwan. Using CRL-related cut-off points for screening is more reasonable than using a fixed cut-off point.

Adult↗
PubMed1998

The effect of fetal neck position on nuchal translucency measurement.

OBJECTIVE: To determine the influence of the position of the fetal neck on nuchal translucency measurement. DESIGN: A prospective cross-sectional study. POPULATION: One hundred and ninety-six. METHODS: Nuchal translucency was measured in the mid-sagittal plane, with the fetal neck in the flexed, neutral and extended positions. Measurements were made to the nearest 0.1 mm. Statistical analysis used the paired t-test for differences between the extended and neutral positions, [delta extended nuchal translucency] and the flexed and neutral positions [delta flexed nuchal translucency]. RESULTS: The mean extended nuchal translucency was 0.62 mm greater than the mean neutral nuchal translucency value [95% confidence interval 0.53 to 0.70, T = 14.33, P < or = 0.00001]. The mean flexed nuchal translucency was 0.40 mm less than the mean neutral nuchal translucency value [95% CI 0.34 to 0.47, T = 11.99; P = < 0.00001]. The repeatability coefficient was lower in the case of neutral nuchal translucency measurements [0.48] and was higher in the other groups [extended = 1.04, flexed = 0.70]. CONCLUSION: Fetal neck position can make a significant difference to nuchal translucency measurements. Repeatability of measurements are more accurate with the fetal neck in the neutral position. These findings have important implications for clinicians using nuchal translucency to screen the general obstetric population.

Cross-Sectional Studies↗
PubMed2001

[Fetal nuchal translucency measurements in women aged 35 and older. Results from 1.1. 99-31.12.00.].

OBJECTIVE: Based on a combination of ultrasound fetal nuchal translucency measurement at 11-13 weeks and maternal age, a risk assessment for fetal aneuploidy is calculated. This method identifies a subgroup at risk for fetal aneuploidy, with less invasive testing while increasing the number of fetal aneuploidy cases diagnosed, compared to the current approach in Iceland where fetal aneuploidy risk is based on maternal age only. MATERIAL AND METHODS: All women who presented for an ultrasound and counselling in preparation for an amniocentesis, the majority for advanced maternal age, were offered nuchal translucency measurement and risk assessment for fetal aneuploidy. RESULTS: In 1999 a total of 477 nuchal translucency measurements were performed. Ten fetuses (2.1%) had risk assessment for fetal aneuploidy above 1:300 leading to diagnosis of 5/6 (83%) trisomy 21 cases and two other fetal aneuploidy cases within the group. Three fetuses who had increased nuchal translucency and normal karyotype were normal at birth. Three women who underwent an amniocentesis in spite of risk assessment less then 1:300 had aneuploid fetuses. Ultrasound and nuchal translucency measurement lead to the diagnosis of 7/10 fetal aneuploidy cases within the group. In 2000 a total of 418 nuchal tranlucency measurements were performed. Nine fetuses (2.15%) had risk assessment for fetal aneuploidy above 1:300 leading to diagnosis of 1/1 trisomy 21 case and 2/2 other fetal aneuploidy cases within the group. One fetus had multiple anomalies and the pregnancy was terminated without prior karyotyping. Of the five fetuses who had a normal karyotype one had cardiac abnormality and one an omphalocele. The remaining three were healthy at birth. Ultrasound and fetal nuchal translucency measurements lead to the diagnosis of all fetal aneuploidy cases within the group. CONCLUSIONS: During 1999 and 2000 ultrasound and fetal nuchal translucency measurements in a selected subgroup at risk for fetal aneuploidy lead to the diagnosis of 7/10 and 3/3 fetal aneuploidy cases with 2.1% positive screen rate.

English Abstract↗
PubMed1996

Nuchal translucency measurements: frequency distribution and changes with gestation in a general population.

OBJECTIVE: To investigate nuchal translucency variation with crown-rump length (CRL) in the first trimester in normal fetuses. DESIGN: A prospective observational study. SETTING: Department of obstetrics in a London teaching hospital. PARTICIPANTS: One thousand seven hundred and seven pregnant women (1685 singleton and 22 twin pregnancies) with chromosomally normal fetuses between 9+zero and 14+6 weeks of gestation were recruited sequentially from a dating scan clinic. Nuchal translucency was measured in 94.9% by transabdominal sonography (TAS) and by transvaginal sonography (TVS) if difficulty was encountered with TAS (5.1%). Nuchal translucency measurement was repeated in 136 fetuses: the first scan between between 9+zero-11+6 weeks and the second over 12 weeks of gestation. RESULTS: Of this general population, 4.2% had a nuchal translucency (NT) measurement > or = 2.5 mm, but this proportion varied significantly between gestational age groups (P = 0.011). The repeatability coefficients for NT measurements were 0.44 mm and 0.23 mm for TAS and TVS, respectively. The cross-sectional data demonstrate an increase in nuchal translucency measurement between 9 and 12 weeks of gestation and then a decrease at 13-14 weeks. This relation is best modelled using the quadratic equation: log10 (NT) = -1.03 + (0.0314 x CRL) - (2.20 x 10(-4) x CRL2). Longitudinal data confirmed an increase of nuchal translucency measurements with increasing gestation. CONCLUSION: Nuchal translucency measurements increase significantly with increasing gestation. The use of a single threshold nuchal translucency measurement throughout the first trimester is inappropriate. We propose reference ranges of nuchal translucency measurements with gestation, aiming to improve the performance of nuchal translucency screening for chromosomal abnormalities.

Cross-Sectional Studies↗
PubMed1998

Screening for Down's syndrome by fetal nuchal translucency measurement in a general obstetric population.

OBJECTIVE: To examine the effectiveness of nuchal translucency measurement in the detection of trisomy 21 in a low-risk population. DESIGN: Prospective cohort study. SUBJECTS: A total of 1473 women with viable singleton pregnancies between 10 and 14 weeks' gestation attending an antenatal clinic for routine obstetric care. METHODS: The fetal nuchal translucency was measured in all women. Fetal karyotyping was performed for the usual indications and in cases of a nuchal translucency measurement > or = 3 mm. RESULTS: Down's syndrome was found in nine fetuses (0.6%). Screening by maternal age would have diagnosed six out of nine fetuses (67%) with trisomy 21 for an invasive testing rate of 24%. Because the actual uptake of prenatal diagnosis for maternal age was 79%, only 44% of the Down's syndrome fetuses would have been detected prenatally by this screening method. A nuchal translucency of 3 mm or more identified 67% of the fetuses with trisomy 21, for an invasive testing rate of 2.2%. The combination of nuchal translucency thickness, corrected for the influence of gestation by 'delta-value' and maternal age performs differently according to the chosen cut-off point for adjusted risk. A minimum risk of 1 : 100 would detect 78% of the Down's syndrome fetuses for a testing rate of 8.1%. By offering karyotyping to all women with a post-test risk of 1 : 300, the detection rate would increase to 100% with an invasive testing rate of 19.8%. This is lower than the invasive testing rate of maternal age screening. CONCLUSIONS: These data suggest that nuchal translucency measurement is an effective screening method for trisomy 21 in an unselected obstetric population.

Adolescent↗
PubMed1997

The effect of nuchal translucency measurement on second-trimester biochemical screening for Down's syndrome.

In this study we examined the effect of introducing first-trimester nuchal translucency measurement on the second-trimester maternal serum screening for trisomy 21. The detection rate, false-positive rate, likelihood ratio and positive predictive value of the double marker test before and after introduction of nuchal translucency measurement were determined. The detection rate of nuchal translucency screening for trisomy 21 was 83% (5/6) with a 1.3% false-positive rate, a 63.8 likelihood ratio and a positive predictive value of 22.7%. After the introduction of nuchal translucency measurement, the likelihood ratio for a positive result and positive predictive value of the biochemical screening decreased from 9.1 to 5 and 2.7% to 0.45%, respectively. Our results show that nuchal translucency measurement is not only an effective method of first-trimester screening for Down's syndrome but also has implications for the likelihood ratio and positive predictive value of second-trimester biochemical screening. Since the biochemical test is now applied to a population with a decreased risk of trisomy 21, a positive test will be less likely to indicate Down's syndrome than when nuchal translucency measurement was not applied.

Biomarkers↗
PubMed1998

Screening for Down's syndrome by fetal nuchal translucency measurement in a high-risk population.

OBJECTIVE: To examine the discriminative capacity of nuchal translucency measurement in the detection of trisomy 21 and other chromosomal anomalies. DESIGN: Prospective cohort study. SUBJECTS: A total of 2247 women with viable singleton pregnancies between 10 and 14 weeks' gestation attending a prenatal diagnosis center for fetal karyotyping. METHODS: The fetal nuchal translucency was measured transabdominally in all women before invasive prenatal testing. RESULTS: Chromosomal abnormalities were found in 63 fetuses, including 36 with Down's syndrome. The likelihood of the presence of chromosomal abnormalities increased with larger nuchal translucency thickness. A nuchal translucency of 3 mm or more identified 25 out of 36 fetuses (69%) with trisomy 21 at the expense of a 4.0% false-positive rate. Correction of nuchal translucency measurements for differences due to variation of the measurement with gestational age, either by using the 'delta-value' or multiples of the median (MoM), did not improve the detection rate in our patient data set. CONCLUSIONS: The discriminative capacity of nuchal translucency measurement makes it a useful tool in screening for trisomy 21 and other chromosomal anomalies.

Adult↗
PubMed1998

Weekly nuchal translucency measurements in normal fetuses.

OBJECTIVE: To examine the longitudinal course of nuchal translucency thickness by weekly measurements between 10 and 15 weeks' gestation in normal fetuses. METHODS: Nuchal translucency was measured weekly from 10 to 15 weeks' gestation in 64 fetuses with normal pregnancy outcome. The median and the fifth, 25th, 75th, and 95th percentiles were calculated. RESULTS: Nuchal translucency measurements varied considerably with gestational age; this variation followed a fetus-specific pattern. In 94% of cases, we observed an increase followed by a steady decrease in nuchal translucency measurement. A visible nuchal translucency was found after 76 and 86 days' gestation in 97% (95% confidence interval [CI] 89, 100) and 100% (95% CI 94, 100) of the fetuses, respectively. The median nuchal translucency increased from 0.7 mm at 70 days' gestation to 1.7 mm at 91 days' gestation, after which it declined to 1.0 mm at 105 days' gestation. CONCLUSION: A progressive increase and subsequent decrease in nuchal translucency thickness occurs with advancing gestation in most fetuses, but the timing of the peak thickening appears to be fetus-specific. In this study, each fetus developed a visible nuchal translucency. If the nuchal translucency measurement is 0 mm before 12 weeks, it may be advisable to repeat the measurement at 12 weeks' gestation. In contrast, a nuchal translucency that cannot be measured from 12 weeks' gestation onward suggests that this temporary anatomic entity is already in its waning phase.

Adult↗