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Obstetric
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Nuchal Translucency
Drs Challis, Farine, Morrow, Ritchie, Ryan 01 January 2001
Source: Platypus
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Nuchal translucency refers to the fluid collection behind the fetal neck which is measured between crown rump lengths of 38mm and 84mm , corresponding approximately with 10 to 14 weeks gestation. It is the maximum width of the subcutaneous translucency between the skin and the soft tissue overlying the cervical spine of the fetus. It should not be confused with nuchal (fold) thickness which appears to be a separate entity. Very few cases of increased nuchal translucency progress to raised second trimester nuchal thickness.
It is unknown what pathological nuchal translucency represents but several theories have been advanced to explain it. It is suggested that fluid collects behind the neck, representing the endpoint of one of several pathological processes, in a similar fashion to dependent ankle edema later in life. This is partly because of a tendency on the part of the fetus to lie on its back and partly due to laxity in the skin of the neck. Theories of pathogenesis include: i) cardiac failure related to congenital cardiac abnormality or dysfunction; ii) venous congestion due to chest compression, for example due to an intrathoracic lesion; iii) failure of lymphatic drainage due to neuromuscular problems, for example arthrogryposis causing contractures and flexion deformities; iv) abnormal development of lymphatics; or, v) altered connective tissue composition ,for example the increased elasticity of connective tissue in trisomy 21. It seems not to be a marker for fetal or maternal infection in the first trimester.
Resolution after 14 weeks gestation may occur for a variety of reasons. The lymphatic system may have developed sufficiently to drain away any excess fluid. Furthermore, changes to the placental circulation will result in drop in peripheral resistance. However, a recent study suggested that fetoplacental vascular resistance per se does not contribute to increased nuchal translucency.
It should be noted that nuchal translucency is a feature of both normal and abnormal pregnancies. Further research into the normal anatomical development of the head and neck between the 8th and 14th week will be required to fully understand its’ significance. It may function as a pressure valve. The placenta is undergoing rapid growth with a consequent increase in circulating blood volume. The choroid plexus and other posterior fossa contents are also completing organogenesis at this time and may need to be protected from overperfusion.
Nuchal translucency is related to crown rump length CRL and therefore normally increases with gestational age. This must be taken into account when interpreting results as the critical point for separating ’normal’ from ‘abnormal’ will vary as pregnancy progresses. However, nuchal translucency does not vary with maternal age. Significant differences have been found in nuchal translucency in different ethnic groups but too small to be of clinical significance when screening for Down syndrome.
There is a range of ‘normal’ values for nuchal translucency, for which centile charts and tables exist. Above 3mm is generally considered to be high and about 5% of the population will fall into this group. Only 1-2% of pregnancies will have a translucency greater than 3.5mm.
Increased nuchal translucency is associated with an increase in the risk of chromosomal abnormalities and in fetuses with a normal karyotype, an increase in the risk of other defects, especially cardiac. The greater the measurement, the greater the risk of chromosomal abnormality. At 3mm there is a three-fold increase in the risk of Down syndrome, rising to 36 times the background risk at > 6mm. Conversely, a “normal” measurement correlates with a decreased risk of aneuploidy.
Nuchal translucency may also be a predictor of fetal outcome. About 90% of fetuses with nuchal translucency greater than 3mm at 12 weeks are normal at birth with 10% having major abnormalities. In contrast, only 10% of fetuses with a measurement of greater than 6mm at 12 weeks are normal at birth. As well as Down, increased nuchal translucency is associated with other major aneuploides - trisomy 18, 13, Turner’s Syndrome and triploidy. It is also associated with major congenital abnormalities including cardiac anomalies, diaphragmatic hernia, abdominal wall defects and a number of both genetic syndromes and single gene disorders.
There is a background risk of aneuploidy / congenital abnormality in every pregnancy based on maternal age, previously affected pregnancies and gestational age. The risk increases with maternal age and decreases with advancing gestation. Tables exist for many of the common abnormalities. Importantly, nuchal translucency does not vary with maternal age. This means these two factors can be used independently to refine the risk for an individual pregnancy.
An important application has been in screening for Down Syndrome (trisomy 21) in the first trimester. Nuchal translucency and crown rump length are used in combination with maternal age to refine risk and target diagnostic tests, eg CVS and amniocentesis. There are many studies examining the effectiveness of using nuchal translucency in the first trimester to screen for Down, including large series of unselected pregnancies. Most have used a nuchal translucency of either > 3 mm or > 95th centile in defining high / abnormal results. If amniocentesis is offered to 5% of the population with a calculated risk of 1 in 300 or more, approximately 78% of cases of Down may be detected prenatally. This compares with about 30% if testing is based on maternal age alone and approximately 65% based on maternal serum screening. Even so it should be noted that 30 invasive tests will be required to detect one case of Down Syndrome.
Nuchal translucency is a useful screening tool for aneuploldy in twin pregnancies where serum screening is not applicable. It may also have a small predictive value in the twin-twin transfusion syndrome.
A major advantage of nuchal translucency measurement is to raise suspicion of an abnormal pregnancy much earlier than with traditional screening methods. Invasive diagnostic procedures may be targeted more effectively and counseling and interventions offered at an earlier gestation.
The finding of increased nuchal translucency between 10 and 14 weeks should prompt consideration of karyotyping and, especially in those with normal karyotype, a search for other major congenital abnormalities, including fetal echocardiography.Measurement of nuchal translucency must be performed in a standardized and reproducible fashion by operators trained in the technique. Their measurements should be validated before being used within a screening program. The method developed by the Fetal Medicine Foundation in the U.K. is carried out between 10 and 14 weeks, CRL- The transabdominal approach will be satisfactory 95% of the time but transvaginal imaging can be used in other cases if necessary. Their approach includes the following points.
-A good sagittal section of the fetus, as for measurement of CRL should be obtained.
-The fetus should occupy at least three quarters of the image.
-A careful distinction between fetal skin and amnion should be made as both of these appear as a thin membrane at this gestation. Either wait for or induce fetal movement away from the amnion by asking the mother to cough or tapping the abdomen.
-Measure the maximum thickness of the subcutaneous echolucency between the skin and the soft tissue overlying the cervical spine. The calipers should be placed on the internal edges of the membranes.
-Take more than one measurement and use the mean of two good measurements.
Intra- and inter-observer variability has been demonstrated to be 0.54 and 0.62mm respectively in 95% of cases. As it increases with CRL, gestation must be taken into account when determining whether a given nuchal translucency is raised or not. The position of the fetal neck may be of importance. An extended position gives a greater value (by 0.62mm), whilst the flexed position results in a lesser value (by 0.4mm) than the mean nuchal translucency measured in the neutral position.
A nuchal cord may also bias results adding a mean of 0.8mm to the measurement. This occurs in about 8% of pregnancies at 10-14 weeks. Color Doppler ultrasound may be useful to lower the false positive rate.
A computer program has been developed by the Fetal Medicine Foundation, London, UK. which will calculate the risk based on maternal age, crown rump length and nuchal translucency measurement.
Title: Sonographic scoring index for prenatal detection of chromosomal abnormalities
Author: Benacerraf BR, Neuberg D, Bromley B, Frigoletto FD
Journal: J Ultrasound Med 11: 449-458
Year: 1992
Title: Sonographic measurement of nuchal skinfold thickness for detection of Down syndrome in the second-trimester
fetus: a multicenter prospective study
Author: Grandjean H, Sarramon M-F
Journal: Obstet Gynecol 85: 103-6
Year: 1995
Title: Thickened nuchal fold in fetuses not at risk for aneuploidy
Author: Benacerraf BR, Laboda LA, Frigoletto FD
Journal: Radiology 184: 239-242
Year: 1992
Title: Adjusting the risk for trisomy 21 on the basis of second-trimester ultrasonography
Author: Vintzileos AM, Egan JFX
Journal: Am J Obstet Gynecol 172: 837-844
Year: 1995
Title: Ultrasonographically evident fetal nuchal skin thickening: is it specific for Down syndrome
Author: Toi A, Simpson GF, Filly RA
Journal: Am J Obstet Gynecol 156: 150-3
Year: 1987
Title: Optimal nuchal skin-fold thresholds based on gestational age for prenatal detection of Down syndrome
Author: Gray DL, Crane JP
Journal: Am J Obstet Gynecol 171: 1282-6
Year: 1994
Title: Sonographically measured nuchal skinfold thickness as a screening tool for Down syndrome: results of a
prospective trial
Author: Crane JP, Gray DL
Journal: Obstet Gynecol 77: 533-6
Year: 1991
Title: Ultrasonographic measurement of fetal nuchal skin to screen for chromosomal abnormalities
Author: Watson WJ, Miller RC, Menard K, Chescheir NC, Katz VL, Hansen WF, Wolf EJ
Journal: Am J Obstet Gynecol 170: 583-6
Year: 1994
Title: Prospective multicenter study of second-trimester nuchal skinfold thickness in unaffected and Down syndrome
pregnancies
Author: Donnenfield AE, Carlson DE, Palomaki GE, Librizzi RJ, Weiner S, Platt LD
Journal: Obstet Gynecol 84: 844-7
Year: 1994
Title: Second-trimester sonographic diagnosis of Down syndrome: role of femur-length shortening and nuchal-fold
thickening
Author: Perrella R, Duerinckx AJ, Grant EG, Tessler F, Tabsh K, Crandall BF
Journal: AJR 151: 981-5
Year: 1988
Title: The current role of sonography in the detection of Down syndrome
Author: Hill LM, Guzick D, Belfar HL, Hixson J, Rivello D, Rusnak J
Journal: Obstet Gynecol 74: 620-3
Year: 1989
Title: Nuchal-fold thickening in Down syndrome fetuses: transient appearance and spontaneous resolution in the
second trimester
Author: Itoh H, Ihara Y, Sagawa N, Mori T, Natsuyama E
Journal: J Perinat Med 21: 139-145
Year: 1993
Title: The resolving nuchal fold in second trimester fetuses: not necessarily reassuring
Author: Bromley B, Benacerraf BR
Journal: J Ultrasound Med 14: 253-5
Year: 1995
Title: First-trimester Down's syndrome screening using nuchal translucency: a prospective study in patients
undergoing chorionic villus sampling
Author: Brambati B, Cislaghi C, Tului L, Alberti M, Colombo U, Zuliani G
Journal: Ultrasound Obstet Gynecol 5: 9-14
Year: 1995
Title: Chromosomal defects and outcome in 1015 fetuses with increased nuchal translucency
Author: Pandya PP, Kondylios A, Hilbert L, Snijders RJM, Nicolaides KH
Journal: Ultrasound Obstet Gynecol 5: 15-9
Year: 1995
Title: First-trimester nuchal oedema as a marker of aneuploidy
Author: Comas C, Martinez JM, Ojuel J, Casals E, Puerto B, Borrell A, Fortuny A
Journal: Ultrasound Obstet Gynaecol 5: 26-9
Year: 1995
Title: Fetal nuchal translucency: ultrasound screening for fetal trisomy in the first trimester of pregnancy
Author: Nicolaides KH, Brizot ML, Snijders RJM
Journal: Br J Obstet Gynecol 101: 782-6
Year: 1994
Title: 18. Nicolaides KH, Azar G, Byrne D, Mansur C, Marks K
Fetal nuchal translucency: ultrasound screening for chromosomal defects in first trimester of pregnancy
Author: Nicolaides KH, Azar G, Byrne D, Mansur C, Marks K
Journal: Brit Med J 304: 867-9
Year: 1992
Title: A sonographic sign for the detection in the second trimester of the fetus with Down syndrome
Author: Benacerraf Br, Barss VA, Laboda LA
Journal: Am J Obstet Gynecol 151: 1078-9
Year: 1985
Title: Ultrasonographic detection of the second-trimester fetus with trisomy 18 and trisomy 21
Author: Ginsberg N, Cadkin A, Pergament E, Verlinsky Y
Journal: Ultrasonographic detection of the second-trimester fetus with trisomy 18 and trisomy 21
Year: 1990
Title: Soft tissue nuchal fold in the second-trimester fetus: Standards for normal measurements compared to those in
Down syndrome
Author: Benacerraf BR, Frigoletto FD
Journal: Am J Obstet Gynecol 157: 1146-9
Year: 1987
Title: Sonographic identification of second-trimester fetuses with Downís syndrome
Author: Benacerraf BR, Gelman R, Frigoletto FD Jr
Journal: NEJM 317: 1371-6
Year: 1987
Title: Normal nuchal thickness in the midtrimester indicates reduced risk of Down syndrome in pregnancies with
abnormal triple-screen results
Author: Bahado-Singh RO, Goldstein I, Uerpairojkit B, Copel JA, Mahoney MJ, Baumgarten A
Journal: Am J Obstet Gynecol 173: 1106-10
Year: 1995
Title: Can the risk for Down syndrome be reliably modified by second-trimester ultrasonography?
Author: Palomaki GE, Haddow JE
Journal: Am J Obstet Gynecol 173: 1639-40
Year: 1995
Title: Early amnioccentesis and fetal nuchal translucency in women requesting karyotyping for advanced maternal age
Author: Salveson DR, Goble O
Journal: Prenat Diagn 15: 971-4
Year: 1995
Title: Can the presumed risk of autosomal trisomy be decreased in fetuses of older women following a normal
sonogram?
Author: Nadel AS, Bromley B, Frigoletto FD Jr, Benacerraf BR
Journal: J Ultrasound Med 14: 297-302
Year: 1995
Title: Increased first trimester nuchal translucency as a prenatal manifestation of Smith Lemli-Opitz syndrome
Author: Hyett JA, Clayton PT, Moscoso G, Nicolaides KH
Journal: Am J Med Genet 58: 374-6
Year: 1995
Title: Screening for fetal trisomies by maternal age and fetal nuchal translucency thickness at 10 to 14 weeks of
gestation
Author: Pandya PP, Snijders RJM, Johnson SP, Brizot M de L, Nicolaides KH
Journal: Brit J Obstet Gynaecol 102: 957-962
Year: 1995
Title: What is fetal nuchal translucency?
Author: Berger A
Journal: 1999 Jan 9;318(7176):85.
Year: 1999
Title: Outcome of fetuses with enlarged nuchal translucency and normal karyotype.
Author: Bilardo CM, et al.
Journal: Ultrasound Obstet Gynecol. Jun;11(6):401-6.
Year: 1998
Title: Nuchal translucency.
Author: Blakemore KJ
Journal: Ultrasound Obstet Gynecol. Jun;11(6):388-90.
Year: 1998
Title: Ultrasound screening for fetal abnormalities in the first trimester.
Author: Chitty,L. & Pandya,P.P.
Journal: Prenat Diagn. 17(13):1269-81.
Year: 1997
Title: Results of routine fetal nuchal translucency measurement at weeks 10-13 in 4233 unselected pregnant women.
Author: Hafner E, et al.
Journal: Prenat Diagn. Jan;18(1):29-34.
Year: 1998
Title: Screening for chromosomal abnormalities in an unselected population by fetal nuchal translucency.
Author: Hafner E; Schuchter K; Philipp K
Journal: Ultrasound Obstet Gynecol Nov;6(5):330-3
Year: 1995
Title: Abnormalities of the heart and great arteries in chromosomally normal fetuses with increased nuchal
translucency thickness at 11-13 weeks of gestation.
Author: Hyett J; Moscoso G; Papapanagiotou G; Perdu M; Nicolaides KH
Journal: Ultrasound Obstet Gynecol Apr;7(4):245-50
Year: 1996
Title: Increased nuchal translucency at 10-14 weeks of gestation as a marker for major cardiac defects.
Author: Hyett JA, et al.
Journal: Ultrasound Obstet Gynecol. Oct;10(4):242-6.
Year: 1997
Title: Intrauterine lethality of trisomy 21 fetuses with increased nuchal translucency thickness.
Author: Hyett JA; Sebire NJ; Snijders RJ; Nicolaides KH
Journal: Ultrasound Obstet Gynecol Feb;7(2):101-3
Year: 1996
Title: Screening for fetal trisomies by maternal age and fetal nuchal translucency thickness at 10 to 14 weeks of
gestation.
Author: Mol BW, et al.
Journal: Br J Obstet Gynaecol. Oct;103(10):1051-2.
Year: 1996
Title: Increased fetal nuchal translucency: possible involvement of early cardiac failure.
Author: Montenegro N, et al.
Journal: Ultrasound Obstet Gynecol. Oct;10(4):265-8.
Year: 1997
Title: Fetal nuchal translucency: a need to understand the physiological basis.
Author: Moscoso G
Journal: Ultrasound Obstet Gynecol. Jan;5(1):6-8.
Year: 1995
Title: Assessment of fetal nuchal translucency test for Down's syndrome.
Author: Neilson JP
Journal: Lancet. Sep 13;350(9080):754-5.
Year: 1997
Title: Chromosomal defects and outcome in 1015 fetuses with increased nuchal translucency.
Author: Pandya PP, et al.
Journal: Ultrasound Obstet Gynecol. Jan;5(1):15-9.
Year: 1995
Title: Screening for fetal trisomies by maternal age and fetal nuchal translucency thickness at 10 to 14 weeks of
gestation.
Author: Pandya PP, et al.
Journal: Br J Obstet Gynaecol. Dec;102(12):957-62.
Year: 1995
Title: Nuchal translucency thickness and crown-rump length in twin pregnancies with chromosomally abnormal
fetuses.
Author: Pandya PP; Hilbert F; Snijders RJ; Nicolaides KH
Journal: J Ultrasound Med Aug;14(8):565-8
Year: 1995
Title: The effect of nuchal cord on nuchal translucency measurement at 10-14 weeks.
Author: Schaefer M, et al.
Journal: Ultrasound Obstet Gynecol. Apr;11(4):271-3.
Year: 1998
Title: The distribution of nuchal translucency at 10-13 weeks of pregnancy.
Author: Schuchter K, et al.
Journal: Prenat Diagn. Mar;18(3):281-6.
Year: 1998
Title: Establishment and application of a normal range for nuchal translucency across the first trimester.
Author: Scott F, et al.
Journal: Prenat Diagn. Jul;16(7):629-34.
Year: 1996
Title: Increased nuchal translucency thickness at 10-14 weeks of gestation as a predictor of severe twin-to-twin
transfusion syndrome.
Author: Sebire NJ, et al.
Journal: Ultrasound Obstet Gynecol. Aug;10(2):86-9.
Year: 1997
Title: Increased fetal nuchal translucency thickness at 10-14 weeks: is screening for maternal-fetal infection
necessary?
Author: Sebire NJ, et al.
Journal: Br J Obstet Gynaecol. Feb;104(2):212-5.
Year: 1997
Title: Screening for trisomy 21 in twin pregnancies by maternal age and fetal nuchal translucency thickness at 10-14
weeks of gestation.
Author: Sebire NJ, et al.
Journal: Br J Obstet Gynaecol. Oct;103(10):999-1003.
Year: 1996
Title: Fetal karyotyping in twin pregnancies: selection of technique by measurement of fetal nuchal translucency
Author: Sebire NJ; Noble PL; Psarra A; Papapanagiotou G; Nicolaides KH
Journal: Br J Obstet Gynaecol Sep;103(9):887-90
Year: 1996
Title: UK multicentre project on assessment of risk of trisomy 21 by maternal age and fetal nuchal-translucency
thickness at 10-14 weeks of gestation. Fetal Medicine Foundation First
Author: Snijders RJ, et al.
Journal: Lancet. Aug 1;352(9125):343-6.
Year: 1998
Title: Defects and syndromes in chromosomally normal fetuses with increased nuchal translucency thickness at
10-14 weeks of gestation.
Author: Souka AP, et al.
Journal: Ultrasound Obstet Gynecol. Jun;11(6):391-400.
Year: 1998
Title: Evaluation of first-trimester screening by fetal nuchal translucency and maternal age.
Author: Theodoropoulos P, et al.
Journal: Prenat Diagn. Feb;18(2):133-7.
Year: 1998
Title: Effect of first-trimester nuchal translucency on second-trimester maternal serum biochemical screening for
Down's syndrome.
Author: Thilaganathan B, et al.
Journal: Ultrasound Obstet Gynecol. Oct;10(4):261-4.
Year: 1997
Title: The effect of fetal neck position on nuchal translucency measurement.
Author: Whitlow BJ, et al.
Journal: Br J Obstet Gynaecol. Aug;105(8):872-6.
Year: 1998
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