Screening performance of first trimester nuchal translucency, ductus venosus blood flow and tricuspid regurgitation for cardiac defects

The present article summarises current knowledge on the risk of fetal cardiac malformations in fetuses with increased nuchal translucency (NT), abnormal ductus venosus blood flow pattern and tricuspid regurgitation. The risk of congenital heart disease (CHD) increases with increasing NT. However, nuchal translucency screening is only modestly efficient in the detection of congenital heart disease in low-risk pregnancies. If the nuchal translucency is normal, abnormal ductus venosus blood flow and tricuspid regurgitation show low sensitivities as single screening parameters. The combination of all 3 markers might increase the detection rates. Fetal echocardiography at 20 weeks of gestation is recommended in foetuses with an NT ≥95th percentile, as the incidence of CHD increases 2.5-fold. When the NT measurement is ≥99th percentile, the risk of CHD increases 10-fold. In this high-risk group and in fetuses with tricuspid regurgitation and/or an abnormal DV flow pattern along with an increased NT, first or early second trimester echocardiography performed by experts is warranted. The early examination of the fetal heart should be completed by a detailed echocardiogram at around 20 weeks of gestation.     

Structural heart defects associated with an increased nuchal translucency: 9 years experience in a referral centre

OBJECTIVE: To investigate the congenital heart disease (CHD) found in association with an increased nuchal translucency (NT) at 11-14 weeks of gestation in chromosomally normal and abnormal fetuses. METHODS: Patients referred from January 1998 until May 2007 with an increased NT (> or = 95th percentile) where CHD was diagnosed were included. Chromosome analysis, fetal and postnatal echocardiography were performed. A postmortem examination followed pregnancy termination when possible. RESULTS: Major CHD was identified in 68 of 967 fetuses with an increased NT (median NT 4.8 mm, range 2.5-22 mm).Major CHD was found in 34 of 693 fetuses (4.9%) with a normal karyotype and increased NT (median 5.2 mm, range 2.5-9.6 mm). CHD frequency increased from 1.9%, with NT between 2.5 and 3.5 mm, to 27.7% when NT was > or = 6.5 mm. Septal defects predominated (20%) when NT was < or = 3.5 mm. With NT > 3.5 mm an equal distribution of CHD types was seen.Major CHD was identified in 34 of the 274 fetuses with an abnormal karyotype and increased NT (median 4.2 mm, range 2.5-22 mm). CONCLUSIONS: A variety of CHD is associated with an increased NT in the first trimester of pregnancy. Conotruncal defects, branchial arch derivative defects, left and right obstructive lesions (inflow and outflow) and shunts were seen.     

Increased nuchal translucency and congenital heart defects in a low-risk population

OBJECTIVE: Increased first-trimester nuchal translucency (NT) is a possible marker for congenital heart defects in euploid fetuses. In this study, we wanted to determine the sensitivity for congenital heart defects using the 95th centile of the NT as a cut-off point. METHODS: All women who booked for delivery in our hospital in the first trimester underwent NT measurement at a crown-rump length (CRL) of between 35 and 75 mm. In all euploid fetuses and newborns with isolated or associated CHD, NT was examined retrospectively and classified as normal (<95th centile according to CRL-dependent centiles in our own data) or increased (> or =95th centile). RESULTS: From a total of 12,978 euploid fetuses screened, 27 had CHD (22 isolated and 5 cases associated with additional malformations). Moreover, 7 of the 27 fetuses also had increased NT (26%). Increased NT was significantly more frequent in fetuses with associated CHD (4/5) than in those with isolated CHD (3/22, Yates corrected chi2 p=0.012). In fact, the relative risk for CHD was 6.6 times higher in fetuses with increased NT compared to those with normal NT. CONCLUSION: Increased NT for the detection of CHD performed less well than in other studies. Nevertheless, it can be used as an indication for fetal echocardiography.     

Fetal cardiac defects and increased nuchal translucency thickness: a prospective study

OBJECTIVE: The purpose of this study was to examine prospectively the association between increased nuchal translucency thickness and major cardiac defects in chromosomally normal fetuses. STUDY DESIGN: A prospective cohort study of 263 chromosomally normal fetuses with an increased nuchal translucency thickness at 11 to 14 weeks of gestation at a tertiary referral center was performed. The incidence of major cardiac defects was examined in relation to the fetal nuchal translucency thickness at the 11 to 14 week ultrasound examination. RESULTS: The nuchal translucency thickness measurements ranged from 2.2 to 8.0 mm (median, 3.1 mm). There were 13 cases of major cardiac defects in this cohort, which gave a prevalence of 49.4 of every 1000 fetuses. With the use of the 99th percentile of nuchal translucency thickness, the prevalence rose to 106.7 of every 1000 fetuses. CONCLUSION: In this population of chromosomally normal fetuses with an increased nuchal translucency thickness, the incidence of cardiac defects was high, which suggests that fetal echocardiography is indicated in this group.     

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.     

Ductus venosus flow velocities in relation to the cardiac defects in first-trimester fetuses with enlarged nuchal translucency

OBJECTIVE: Our aim is to study first-trimester ductus venosus (DV) velocities in relation to cardiac abnormalities. STUDY DESIGN: Ultrasound examination was performed in 85 normal fetuses and 45 fetuses with a nuchal translucency (NT) >95th percentile. Pulsatility index for veins (PIV) and velocity during late diastole (a-V) of the DV were measured and compared with the use of multilevel analysis, between fetuses with a heart defect and those without. RESULTS: Compared with 85 normal fetuses, the a-V and PIV of the fetuses with NT>95th percentile and normal hearts were decreased and increased, respectively. The a-V and PIV of 11 fetuses with NT>95th percentile and cardiac defects were decreased and increased compared with the 25 fetuses with normal hearts, irrespective of the karyotype. The most common cardiac malformations were septal defects. CONCLUSION: Fetuses with NT >95th percentile and cardiac defects show markedly changed DV velocities. Because the type of cardiac defects cannot always explain the hemodynamic changes found in these fetuses, some other mechanisms seem to be involved.     

Nuchal translucency and cardiac abnormalities in euploid singleton pregnancies

Abstract

Objective: To investigate different cut-off levels of nuchal translucency (NT) to predict abnormal cardiac findings (ACF) in second trimester ultrasound examination and confirmed postnatal congenital heart defects (CHD) in euploid pregnancies.

Methods: A retrospective analysis was performed on singleton pregnancies examined in our ultrasound units from 2006 to 2011. Fetuses with an abnormal karyotype were excluded. Different cut-off levels of NT thickness were analyzed to evaluate its performance to detect the ACF on second trimester ultrasound (2nd US) examination and also the CHD detected in neonatal follow-up evaluation of ACF cases.

Results: Of the 12?840 cases, a total number of 8541 euploid pregnancies were included in the study. Thirty-three had ACFs detected by 2nd US (3.86/1000). The mean NT thickness was found to be higher in fetuses with ACFs (p?<?0.0001). Of 33 ACFs, 17 (52%, 1.99/1000) had major CHDs in neonatal follow-up. The area under the ROC curves for NT thickness to predict ACFs and CHDs were 0.67 and 0.65, respectively.

Conclusions: Higher NT thickness is associated with higher risk of ACF. NT is a weak predictor of ACF and major CHD; however, fetuses with an unexplained increase in NT measurement should be referred for further cardiac investigations.     

Screening performance of first-trimester nuchal translucency for major cardiac defects: a meta-analysis

OBJECTIVE: The purpose of this study was to evaluate the screening performance of increased first-trimester nuchal translucency for the detection of major congenital heart defects. STUDY DESIGN: A meta-analysis based on MEDLINE and EMBASE searches (up to June 2002) that assessed the diagnostic performance of increased nuchal translucency for congenital heart defect detection. Weighted sensitivity and specificity estimates (random effects) and summary receiver-operating characteristic curves were obtained. RESULTS: Eight independent studies with 58,492 pregnant women were analyzed. There was significant heterogeneity among the studies. Nuchal translucency above the 99th percentile had a sensitivity of 31% and specificity of 98.7% (random effects calculations), with a positive likelihood ratio of 24. Summary receiver-operating characteristic estimates were consistent with these values. The ability of nuchal translucency measurements above this threshold to detect cardiac malformations varied nonsignificantly (P=.64) for different congenital heart defects types (sensitivity range, 25%-55%). CONCLUSION: Nuchal translucency screening is a modestly efficient strategy for congenital heart defect detection; the use of the 99th percentile threshold may capture approximately 30% of congenital heart defects.     

Detection of congenital heart defects throughout pregnancy; impact of first trimester ultrasound screening for cardiac abnormalities

Objective: To evaluate prospectively the efficacy to screen for congenital heart defects (CHD) during the first trimester nuchal translucency (NT) ultrasound examination by assessing the four chambers’ view of fetal heart. Methods: Pregnancies that were examined prospectively by ultrasound in the first trimester (11th–14th week), the second (19th–24th week) and third trimester were included in the study. 3774 fetuses were examined and fetal heart was assessed during the NT scan by examining the four chambers view. Detailed echocardiography was performed during the anomaly and growth scans. Diagnosis of congenital heart defects (CHD) was further confirmed by a fetal cardiologist. Results: The four chambers view was obtained in 99.52% of the cases. CHD were diagnosed in 29 fetuses (0.77%). Thirteen cases (44.8%) were detected during the 11–13 weeks’ scan, 14 cases (48.3%) during the anomaly scan, 1 CHD (3.5%) during the third trimester scan and 1 case (3.5%) postpartum. Conclusion: Assessment of the four chambers of fetal heart early in pregnancy was feasible and allowed the detection of 45% of CHD. Additional parameters of fetal cardiac anatomy during the NT scan may further improve the detection rate providing pregnancy management information early in the first trimester.     

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

OBJECTIVE: To report our experience with first-trimester screening for trisomy 21 by using the combination of nuchal translucency thickness and nasal bone assessment. METHODS: Pregnant women from a predominantly Latin American population consisting of patients at both low risk and high risk for chromosomal defects underwent first-trimester ultrasonographic screening. Nuchal translucency thickness and nasal bone were assessed by two accredited fetal medicine specialists. Cases of trisomy 21 were identified from the cytogenetics laboratory logbook. RESULTS: Over a 3-year period, 1,287 consecutive singleton pregnancies were screened. The median maternal age was 33 years (range 14-47 years), with 456 (35.4%) women aged 35 years or older at the time of the scan. Overall, 110 fetuses (8.5%) had nuchal translucency thickness greater than the 95th percentile for gestational age and 25 (1.9%) had absent nasal bone. Trisomy 21 was diagnosed in 31 cases. Among them, the nuchal translucency thickness was increased in 28 and the nasal bone was absent in 13 (detection rates of 90.3% and 41.9%, respectively; P<.01). All but one (92.3%) of the trisomy 21 fetuses with absent nasal bone had increased nuchal translucency. Only two of the normal fetuses had an absent nasal bone in the first trimester. CONCLUSION: In our population, increased nuchal translucency thickness is the most important ultrasonographic marker of trisomy 21. In contrast, the nasal bone seems to have a less prominent role in identifying the fetus at risk for trisomy 21 due to its lower detection rate. However, an absent nasal bone should be considered as a highly predictive marker of trisomy 21.     

Early diagnosis of major cardiac defects in chromosomally normal fetuses with increased nuchal translucency.

OBJECTIVE: To determine the value of early ultrasound examination for prenatal diagnosis of cardiac defects in chromosomally normal fetuses with increased nuchal translucency thickness at 10-14 weeks of gestation. DESIGN: Prospective audit. SETTING: Fetal Medicine Centre. METHODS: Specialist fetal echocardiography was carried out in 398 chromosomally normal fetuses with a nuchal translucency measurement above the 99th centile (> or = 3.5 mm). In the first 75 pregnancies the cardiac scan was carried out at 17-22 weeks and the next 323 cases had one scan at 13-17 weeks and another at 20-22 weeks. Pregnancy outcome was obtained in all of the cases. RESULTS: Major cardiac defects were present in 29 (7.3% of 398) cases and in 28 of these the diagnosis was made by antenatal echocardiography. In 27 of the 29 fetuses with major cardiac defects echocardiography was carried out at 13-17 weeks and an abnormality was suspected in 24 of the cases (88%). CONCLUSIONS: Increased nuchal translucency in chromosomally normal fetuses is associated with an increased prevalence of major cardiac defects and, as such, is an indication for specialist fetal echocardiography. Most of the cardiac abnormalities are detectable on antenatal fetal echocardiography and many can be excluded by early scanning.     

Increased nuchal translucency with normal karyotype

Increased fetal nuchal translucency (NT) thickness between 11 and 14 weeks' gestation is a common phenotypic expression of chromosomal abnormalities, including trisomy 21. However, even in the absence of aneuploidy, nuchal thickening is clinically relevant because it is associated with an increase in adverse perinatal outcome caused by a variety of fetal malformations, dysplasias, deformations, dysruptions, and genetic syndromes. Once the presence of aneuploidy is ruled out, the risk of perinatal outcome dose not statistically increase until the nuchal translucency measurement reaches 3.5 mm or more (>99th percentile). This increase in risk occurs in an exponential fashion as the NT measurement increases. However, if the fetus survives until midgestation, and if a targeted ultrasound at 20 to 22 weeks fails to reveal any abnormalities, the risk of an adverse perinatal outcome and postnatal developmental delay is not statistically increased.     

Testing for 22q11 microdeletion in 146 fetuses with nuchal translucency above the 99th percentile and a normal karyotype

The aim of this study was to examine the value of testing for a 22q11 microdeletion in fetuses with nuchal translucency (NT) above the 99th percentile (>3.5 mm). A 22q11 microdeletion results in the development of 22q11 deletion syndrome, a spectrum of disorders also known as DiGeorge/Velocardiofacial syndrome. A total of 146 pregnancies met the inclusion criteria of NT >3.5 mm between 11+2 and 13+6 weeks' gestation, no structural malformation and normal karyotype. Chorionic villi samples were tested with either multiplex ligation-dependent probe amplification (MLPA) or fluorescent in situ hybridization (FISH) analysis for 22q11 microdeletion. None were diagnosed with the microdeletion. The estimated prevalence of 22q11 microdeletion in these otherwise normal fetuses with increased NT is below 2.7%.     

First-trimester screening for trisomy 21 in twin pregnancy: does the addition of biochemistry make an improvement?

OBJECTIVE: To evaluate the effectiveness of the addition of first-trimester biochemistry to fetal nuchal translucency (NT) measurement in the Combined Test when screening for trisomy 21 in twin pregnancies. METHODS: Maternal serum free beta-hCG and PAPP-A were determined at 8 to 12 weeks and fetal NT was measured at 11 to 14 weeks. The individual risks were estimated for each of the fetuses using both NT screening alone and the Combined Test. An invasive diagnostic procedure was offered when the risk was 1:250 or over in either one of the fetuses. In the first period, only the results of NT screening were clinically applied. After previous analysis, the Combined Test was introduced into clinical practice. RESULTS: In the two-and-a-half-year study period, a complete follow-up was obtained in 100 twin pregnancies. Three fetuses (two pregnancies) with trisomy 21 were detected by both methods. The false-positive rate achieved by NT screening (14.3% of pregnancies and 8.6% of fetuses) was substantially reduced when first-trimester biochemistry was added in the Combined Test (5.1% of pregnancies and 3.6% of fetuses). CONCLUSION: The Combined Test appears to maintain the detection rate achieved by NT screening for trisomy 21 in twin pregnancies, but false-positive rates and invasive diagnostic procedures are reduced.     

Increased nuchal translucency and cystic hygroma in the first trimester: prenatal diagnosis and neonatal outcome

OBJECTIVE: A prospective study of pregnancy outcome in fetuses with increased nuchal translucency above the 95th centile (group NT) or cystic hygroma (group CH) at 10 to 14 weeks of gestation was performed. PATIENTS AND METHODS: Maternal and fetal data (nuchal translucency, caryotype, pregnancy outcome) and infant follow-up of 223 fetuses with first trimester nuchal translucency thickness (183 NT and 40 CH) were analysed. RESULTS: The measurement of nuchal translucency thickness shows a significant difference between group CH and NT (7.4+/-2.9 mm compared 3.7+/-0.8 mm). Chromosomal abnormalities were present in 55% (22/40) in group CH, with 9 cases/22 (40.9%) of Turner syndrome, compared with 14.2% (26/183) in group NT with trisomy 21 in 15 cases/26 (57.7%) (P<0.05). The rate of unfavourable outcome of pregnancy (spontaneous abortion, elective termination of pregnancy, serious structural anomalies) was 80% (32/40) in group CH compared with 18% (33/183) in group NT (P<0.05). In chromosomally normal pregnancies, the rate of fetus with no visible serious structural anomalies was 44.4% (8/18) in group CH compared with 93% (146/157) in group NT (P<0.05). DISCUSSION AND CONCLUSION: Our data show ultrasonographic evaluation of the fetal nuchal translucency thickness at the first trimester is actually indispensable. Neonatal outcome and malformation rate in fetuses with increased nuchal translucency or cystic hygroma are different, even with normal karyotype.     

Can discordance in CRL at the first trimester predict birth weight discordance in twin pregnancies?

Abstract Objective: To examine the correlation between measurements of crown rump length (CRL), nuchal translucency (NT), and birth weight in dichorionic (DC) and monochorionic (MC) twin pregnancies. Methods: A retrospective analysis was performed on all twin term pregnancies delivered between 2001 and 2007 at the McGill University Health Center. Data collected included maternal age, CRL and NT measurement, results of glucose challenge test, birth weight and length, gestational age at delivery, and fetal gender. Results: The study population comprised 792 fetuses: 94 MC/DA and 698 DC/DA. Maternal age, gestational age at delivery, birth weight, and birth length were all significantly higher for the DC group. Male fetuses had significantly higher NT and higher birth weight than female fetuses. Discordance in CRL was found to correlate with discordance in birth weight in the entire study population (P<0.0001, R=0.25), in the DC twins (P<0.0001, R=0.275), but not in MC twins (R=0.10, P=0.33). CRL discordance above the 90th percentile (>12%) predicted 14/40 pregnancies with birth weight discordance above the 90th percentile (>24%) [P<0.001, LR=4.1 (2.6-6.2)]. CRL discordance above the 95th percentile (>16%) predicted 5/21 pregnancies with birth weight discordance above the 95th percentile (>30%) [P<0.001, LR=5.5 (2.6-10.4)]. NT discordance was correlated with CRL discordance (R=0.15, P<0.0001), but not with birth weight, regardless of chorionicity or gender. Conclusion: In twin pregnancies, CRL discordance in first trimester can predict discordance of more than 25% in neonatal birth weight.     

Cribado de aneuploidía en gestación gemelar: resultados de la aplicación del test combinado

Objective

To evaluate the effectiveness of the Combined Test for trisomy 21 screening in twin pregnancies. To assess the performance of biochemical markers and nuchal translucency (NT) measurement in pregnancies with euploid fetuses and in twin pregnancies with one or two affected fetuses. To compare the value of markers according to chorionicity and the mode of conception.

Material and methods

Retrospective study including 161 twin pregnancies. Maternal serum fß-hCG and PAPP-A were determined at 8 to 12 weeks and fetal NT was measured at 11 to 14 weeks. The individual risk of trisomy 21 was calculated in each fetus using the Combined Test. In monochorionic pregnancies, the single risk for the pregnancy was obtained with the largest NT. An invasive diagnostic procedure was offered when the risk was 1:250 or more in one or both of the fetuses.

Results

All trisomy 21 pregnancies were identified (three pregnancies and four fetuses) by the combined testfor a false-positive rate of 6.4% of pregnancies and 3.5% of fetuses. The median fß-hCG level, expressed in MoM, was 1.72 and the median PAPP-A level was 2.01. The median NT was 1.05 MoM. Both fß-hCG and PAPP-A levels were significantly decreased in monochorionic pregnancies and PAPP-A was significantly decreased in pregnancies resulting from assisted reproduction. No significant differences were observed in NT measurement between monochorionic and dichorionic fetuses or between those conceived naturally or by assisted reproduction.

Conclusions

The combined test shows high sensitivity and specificity in screening for trisomy 21 in twin pregnancies. The differences obtained in the biochemical markers according to chorionicity or the mode of conception require confirmation in further studies with a larger number or cases.     

Screening for fetal aneuploidies and fetal cardiac abnormalities by nuchal translucency thickness measurement at 10-14 weeks of gestation as part of routine antenatal care in an unselected population.

OBJECTIVES: To evaluate first trimester pregnancy screening for fetal aneuploidy and congenital heart defects by maternal age and nuchal translucency measurement and screening for fetal aneuploidies and congenital heart defects by ultrasound in an unselected population. DESIGN: A prospective study. SETTING: Fetal medicine unit, St George's Hospital, London. SAMPLE: 4523 consecutive viable fetuses at 10-14 weeks with a crown-rump length between 38 and 80 mm were scanned transabdominally (93%) or transvaginally (7%). METHODS: Screening was performed by calculating the background risk from maternal age, gestational age and obstetric history, which was then adjusted with the nuchal translucency measurement in relation to crown-rump length (adjusted risk). MAIN OUTCOME MEASURES: Measurements of crown-rump length and nuchal translucency thickness. An adjusted risk of > 1:270 was considered as a positive screening test. Pregnancy outcome was obtained through karyotyping, outcome questionnaires and examination of the newborn infants. RESULTS: Mean maternal age was 29-4 years and mean gestational age 12.2 weeks. Screening was positive in 230/4523 fetuses (5.1%), when the adjusted risk (mean 1:2649) was > 1:270. Fetal karyotype was abnormal in 23 (0.51%) cases, including twelve with trisomy 21, five trisomy 18, one trisomy 13, one trisomy 10, one monosomy X and two triploidies. For a false positive rate of 4.7%, the sensitivity of this test was 78% in detecting any fetal aneuploidy. Only one out of nine major congenital heart defects in this population was found within the 110 euploid fetuses with increased nuchal translucency thickness (> 2.5 mm). CONCLUSION: Screening for fetal aneuploidy by maternal age and nuchal translucency measurement can be effective in an unselected population. However, our results do not support its effectiveness in the detection of cardiac abnormalities.     

Fetal nuchal translucency thickness and risk for chromosomal defects

In normal pregnancy fetal nuchal translucency (NT) thickness increases with gestation, in trisomy 21 and other major chromosomal defects fetal NT is increased. The risk for trisomies can be derived by multiplying the a priori maternal age and gestation related risk by a likelihood ratio, which depends on the degree of deviation in fetal NT measurement from the normal median for that crown-rump length. In a pregnant population with a mean maternal age of 28 years, using the risk cut-off of 1 in 300 to define the screen positive group would detect about 80% of trisomy 21 fetuses for a false positive rate of 5%. It was estimated that, for a 5.4% false positive rate, 90% of trisomy 21 fetuses could be detected. Prospective studies have demonstrated that such results are achievable by screening with fetal NT and maternal serum free b-hCG and PAPP-A in the first-trimester. It is therefore essential that, in screening, attention is paid to the provision of high quality sonographic and biochemical services for early diagnosis of chromosomal defects.     

Cystic hygromas, nuchal edema, and nuchal translucency at 11-14 weeks of gestation

OBJECTIVE: To estimate the incidence of septations in fetuses with increased nuchal translucency (NT) thickness, and to investigate the relationship between the length and thickness of the translucency and whether the length or septations provide useful information concerning the fetal karyotype in addition to that provided by the NT thickness alone. METHODS: We examined 386 fetuses with NT thickness equal to or above the 95th percentile for crown-rump length (CRL). A transverse suboccipitobregmatic section of the fetal head was taken to determine whether the sonolucency was septated, and a midsagittal longitudinal section was used to measure NT thickness, CRL, the longitudinal distance between the occiput and the lower end of the sonolucency toward the fetal sacrum (NT length) and the length between the occiput and the sacral tip (spinal length). Logistic regression analysis was used to investigate the effect on abnormal karyotype of CRL, NT thickness, and percentage of NT length to spinal length. RESULTS: Septations within the translucency were observed in all fetuses. The fetal karyotype was abnormal in 83 (21.5%) pregnancies, and multiple regression showed that the only significant independent predictor of abnormal karyotype was fetal NT thickness. CONCLUSION: Septations within the translucency can be seen in all fetuses, and therefore this feature cannot be used to distinguish between increased NT and cystic hygromas. The length of the translucency is related to its thickness and does not give useful information concerning the fetal karyotype in addition to that provided by the NT thickness alone. LEVEL OF EVIDENCE: II-2.