The risk of aneuploidies such as trisomy 21 tend to increase with age. For example, the risk of Down's syndrome at the 16th week to a 25-year-old woman is 1 in 1000, whereas the risk for a 42-year-old-woman is 1 in 50.
All major chromosomal abnormalities may be excluded by amniocentesis with fetal karyotyping. The general recommendation is that amniocentesis should be offered to women who will be aged greater than 35 years and over at their estimated time of confinement. Invasive procedures like amniocentesis is not recommended to be offered to women based on their aged alone risk. In 2006 only 4% of women were reported on having a diagnostic procedure based on age alone.
There were 1877 Downs syndrome diagnosis in 2006 for England and Wales, 60% (1132) (2) were diagnosed prenatal. With increased performance of screening tests diagnostic procedures are reducing, in the last 3 years they have reduced by 6000 while the prenatal detection rate is steadily increasing (1).
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