Nuchal translucency at 14 wks is suggestive of :
Correct Answer: Down's syndrome
Description: Ans. is a i.e. Down syndrome Friends, before I go into the details of nuchal translucency I want to first explain why I have opted for Down syndrome as the answer and not Turner syndrome, though increased nuchal translucency is seen in both the conditions. My answer is based on the following lines from USG in Obs. & Gynae. by Callen "Johnson et al showed that simple nuchal translucency between 10 and 14 weeks were associated with a 60% incidence of abnormal karyotypes-mostly trisomy 21. Unlike the second trimester experience, in which large cystic hygromas were most often associated with turner syndrome, the 45X karyotype represented a minority of the karyotypic abnormalities in the group of fetuses with first trimester nuchal translucency thickening." Nuchal translucency and its Significance * Nuchal translucency is a thickening of the nuchal soft tissues. Embryos with aneuploidy have an increased amount of fluid in the neck region resulting in increased NT measurement. The maximum thickness of the subcutaneous translucent area between the skin and soft tissue that overlies the fetus spine in the sagittal plane is measured. A cut off of 3mm is used as threshold for an abnormal nuchal translucency in first trimester and 6mm for second trimester (16 - 20 weeks). Best time to assess nuchal translucency in first trimester 10 - 13 weeks. Best approach - Transvaginal (but trans abdominal is also reasonably good). It is best seen in the mid sagittal plane as a sonolucency at the back of fetal neck. Note: Increased nuchal translucency itself is not a fetal abnormality, but rather a marker or soft sign that confers increased risk of fetal abnormality. Causes of Increased nuchal translucency : - Down syndrome (Trisomy 21) - Trisomy 18 - Trisomy 13 -- Turner syndrome -- Klinefelter syndrome -- Triploidy. Nuchal translucency with large cystic hygroma is seen in Turners syndrome. Nuchal translucency with septations carries bad prognosis. Chromosomally normal fetus with increased nuchal translucency is associated with increased risk of : -- Cardiac abnormalitiesdeg -- Diaphragmatic herniadeg -- Anterior abdominal wall defectdeg -- Fetal akinesia/dyskinesia syndromedeg Therefore, ACOG recommends that when nuchal translucency measurement is 3.5 mm or more with a normal karyotype, then targeted sonographic examination or fetal echocardiography or both should be done. Nuchal translucency of > 3mm in 1st trimester identifies 67% of fetus with trisomy 21. Increased nuchal fold thickness (> 6mm) is the most sensitive and specific single ultrasound marker for the mid trimester detection of down syndrome. Extra Edge : Nuchal translucency is the most impoant sonographic marker of aneuploidy in the first trimester whereas, Nuchal fold thickness (NFT) is the most impoant sonographic marker of aneuploidy in second trimester. NT is measured from external surface of the skull to the internal surface of the skin. NFT is measured from the external surface of occipital bone to the external surface of skin. NFT is useful for screening between 14-23 weeks. Cut off value for NFT is 5mm (above which it is considered abnormal). Note: In the first trimester 2 most reliable ultrasonographic markers for detecting Down syndrome? Increased muscal translucency Absent nasal bone.
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Gynaecology & Obstetrics
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