title: Relation between increased fetal nuchal translucency thickness and chromosomal defects.
abstract: OBJECTIVE
  To examine the prevalence and distribution of all chromosomal defects in fetuses with increased nuchal translucency thickness.
  
  
  METHODS
  Assessment of risk for trisomy 21 was carried out by a combination of maternal age and fetal nuchal translucency thickness at 11-13 + 6 weeks. A search of the database was made to identify, first, all singleton pregnancies in which fetal karyotyping was carried out and, second, the cases where the fetal nuchal translucency was equal to or above the 95th centile for fetal crown-rump length. The prevalence and distribution of chromosomal defects were determined for each nuchal translucency category: between the 95th centile for crown-rump length and 3.4 mm, 3.5-4.4 mm, 4.5-5.4 mm, 5.5-6.4 mm, 6.5-7.4 mm, 7.5-8.4 mm, 8.5-9.4 mm, 9.5-10.4 mm, 10.5-11.4 mm, and 11.5 mm or more.
  
  
  RESULTS
  The search identified 11,315 pregnancies. The median maternal age was 34.5 (range 15-50) years, and the median fetal crown-rump length was 64 (range 45-84) mm. The fetal karyotype was abnormal in 2,168 (19.2%) pregnancies, and the incidence of chromosomal defects increased with nuchal translucency thickness from approximately 7% for those with nuchal translucency between the 95th centile for crown-rump length and 3.4 mm to 75% for nuchal translucency of 8.5 mm or more. In the majority of fetuses with trisomy 21, the nuchal translucency thickness was less then 4.5 mm, whereas in the majority of fetuses with trisomies 13 or 18 it was 4.5-8.4 mm, and in those with Turner syndrome it was 8.5 mm or more.
  
  
  CONCLUSIONS
  In fetuses with increased nuchal translucency, approximately one half of the chromosomally abnormal group is affected by defects other than trisomy 21. The distribution of nuchal translucency is different for each type of chromosomal defect.
  
  
  METHODS
  II-3.
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, London, United Kingdom.
authors.forename: Karl Oliver
authors.initials: KO
authors.lastname: Kagan
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Avgidou
authors.forename: Francisca S
authors.initials: FS
authors.lastname: Molina
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Gajewska
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000293:Adolescent; D000328:Adult; D002869:Chromosome Aberrations; D004314:Down Syndrome / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000235:genetics; D005260:Female; D005817:Genetic Counseling; D020022:Genetic Predisposition to Disease; D006801:Humans; D007621:Karyotyping; D008423:Maternal Age; D008875:Middle Aged; D048208:Nuchal Translucency Measurement / Q000379:methods*; D010375:Pedigree; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D015995:Prevalence; D011336:Probability; D012189:Retrospective Studies; D018570:Risk Assessment; D014314:Trisomy; D016216:Ultrasonography, Prenatal / Q000379:methods