The mid-pregnancy ultrasound assessment - More detailed information

The timing of the original pregnancy scan arose because of several factors. The initial quality of early ultrasound machines made diagnosis of anomalies difficult in the early stages of pregnancy, although reasonably accurate dating was possible before the inception of real-time B-mode scanning. With the introduction of amniocentesis for advanced maternal age, an ultrasound scan between 16 and 19 weeks gestation became more valuable, as not only could dates be confirmed, but the optimal site for the introduction of the amniocentesis needle could also be identified. Biochemical screening, initially for neural tube defects, and later for Down's syndrome, rely on ultrasound dates to provide an accurate gestational age.

It is a sign of the pace of change in the use of ultrasound in pregnancy, that we are discussing the changing shape of mid pregnancy assessment, when the issues surrounding the original use of such an application are yet to be resolved. The use of a mid-pregnancy ultrasound assessment, where gestational age can be confirmed, and structural anomalies and markers of chromosomal aneuploidy can be recognised, is still debated. The assessment of newer imaging methods is easier than proving the value of older, well established ones.

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