Authors:
Braithwaite JM. Economides DL.
Institution:
Univ Dept Obstetrics and Gynaecology, The Royal Free Hospital, Pond
Street,London NW3 2QE; United Kingdom.
Title:
Nuchal translucency and screening for Down Syndrome.
Source:
Contemporary Reviews in Obstetrics and Gynaecology. Vol 8(2) (pp5-81), 1996.
Abstract:
Improvement in antenatal detection of Down Syndrome is one of the main objectives in prenatal diagnosis. The results of screening programmes based on maternal age and biochemical screening have so far been disappointing. Recently, there has been much interest in the ultrasonographic examination of the fetal nuchal region for the detection of chromosomal abnormalities. Nuchal translucency (NT) in the first trimester can be measured in all patients using a combination of transabdominal (TAS) and transvaginal (TVS) sonography. Repeatability of measurements performed by experienced examiners is satisfactory using both scan modes, although it is superior with TVS. Sonographers require training in NT measurement, especially assessing their ability to consistently obtain repeatable measurements, prior to implementation of widespread screening programmes. This is usually achieved after 80-100 scans. Both longitudinal and cross-sectional data indicate that NT changes with gestation, and therefore the use of a single NT threshold value to define an increased NT is incorrect. Studies in high risk patients have demonstrated a strong association between an increased NT and chromosomal abnormalities. More recently, studies in low risk populations have confirmed the exciting potential of an NT-based screening programme for chromosomal abnormality detection. Further improvements in first trimester prenatal diagnosis may be achieved by combining NT measurements with maternal serum biochemistry and anomaly scans at 12-13 weeks' gestation using TAS and TVS.
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- 3 How could we tell if there is a substantial risk that if the child were born it would suffer from such physical abnormalities as to be seriously handicapped - e.g. Down Syndrome?
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