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Relation between increased fetal nuchal translucency thickness and chromosomal defects
Karl Oliver Kagan1, Kyriaki Avgidou, Francisca S Molina
1Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, London, United Kingdom.
Obstetrics and Gynecology
|January 6, 2006
Summary
Increased fetal nuchal translucency thickness is linked to a higher prevalence of chromosomal defects, with specific distributions for trisomy 21, trisomies 13/18, and Turner syndrome. Approximately half of abnormal karyotypes are due to defects other than trisomy 21.
Area of Science:
- Prenatal diagnosis
- Fetal medicine
- Genetics
Background:
- Increased nuchal translucency (NT) thickness in fetuses is a known marker for chromosomal abnormalities.
- Risk assessment for fetal aneuploidy typically combines NT measurement with maternal age.
Purpose of the Study:
- To determine the prevalence and distribution of all chromosomal defects in fetuses exhibiting increased NT thickness.
- To analyze how NT thickness correlates with specific chromosomal abnormalities.
Main Methods:
- A database search identified 11,315 singleton pregnancies with fetal karyotyping and NT measurements (≥95th centile).
- Chromosomal defect prevalence was analyzed across NT categories ranging from 3.4 mm to ≥11.5 mm.
Main Results:
- Of 11,315 pregnancies, 19.2% had abnormal fetal karyotypes.
- Chromosomal defect incidence rose with NT thickness, from ~7% (NT 3.4 mm) to 75% (NT ≥8.5 mm).
- NT thickness distribution varied by defect: trisomy 21 (<4.5 mm), trisomies 13/18 (4.5-8.4 mm), and Turner syndrome (≥8.5 mm).
Conclusions:
- In fetuses with increased NT, nearly half of chromosomal abnormalities are not trisomy 21.
- The NT measurement's distribution pattern differs significantly among various chromosomal defects.