Nuchal test and dating
Nuchal test detects 80% of Down's syndrome pregnancies
The Snijders study referred to in this commentary reports an 80% detection rate, but using the same method of analysis others have not been able to emulate as high a rate. The explanation may lie in the expertise of the ultrasound or the organisation of the service. Another explanation is that we may be dealing with different populations. Is nuchal thickness related to fetal size or to fetal maturity? Mittendorf et al have demonstrated useful differences in the normal length of pregnancy according to maternal age, parity and racial origin. Current ultrasound dating relates to the start of the pregnancy but places no attention on the precise length of the pregnancy. Hermanni Boerhaave related interval to delivery for his "dating marker" - the LMP. I propose a similar method using ultrasound. The methodology allows the generation of fully customised charts for maternal age, etc. If nuchal thickening is related more to maturity than to fetal size, the sensitivity of the test may well be improved in different sub-populations.
The use of electronic publishing allows the ready publication of raw data along with the study details. This should be encouraged as it permits readers to confirm the researchers' analysis of the data.
David J R Hutchon
Memorial Hospital, Darlington.
Haddow JE Antenatal screening for Down's syndrome: where are we and where next? Lancet 1998;352:343-6.
Hutchon DJR "Back to the Future" for Hermanni Boerhaave or a rational way to generate ultrasound scan charts for estimating the date of delivery. http://www.obgyn.net/us/cotm/9807/cotm_9807.htm
Competing interests: No competing interests