Sequential testing strategies in prenatal screening for down's syndrome

• Main Author: Vadiveloo, Thenmalar
• Published: University of Glasgow 2010
• Subjects: 618; RG Gynecology and obstetrics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.513306

It is important therefore that maternal smoking is accurately recorded on screening request forms and in this study, the accuracy of self reported smoking status was assessed by analysis of cotinine in serum. Results showed that the percentage of self-reported smokers (24.1%) at booking was significantly lower than the cotinine-validated estimate of 30.1%. Also, smoking was associated with low birth weight, delivery prior to 39 weeks, increased AFP level (3.1%) and reduced hCG level (28.7%) in the second trimester. An increasing AFP level (but not hCG level) was associated with lower birth weight and delivery prior to 39 weeks in both smokers and non smokers but the effect was most marked in smokers. The difference in birth weight between the highest and the lowest AFP category for non-smokers was 448.3g and for smokers was 619.2g, suggesting that smoking exacerbates the effect of an elevated AFP on birth weight. Overall the difference in birth weight between the lowest AFP category in non smokers and the highest AFP category in smokers was 931.6g. Summary In summary, this study has shown that a cross-trimester contingent screening protocol with repeat measures has the potential to meet the UK NSC aspirational standard of 90% detection of Down’s syndrome pregnancies with a screen positive rate of less than 2%. Around 90% of women would complete screening in the first trimester without the need for a second stage sequential test. Correcting for factors such as maternal smoking habits, ethnicity and ART would further improve screening performance. Also it has been shown that where ultrasound resources are scarce, within-trimester and across-trimester protocols can reduce the need for NT measurement in all women and still deliver excellent screening performance although this falls short of the higher performance standard. The potential of these new screening protocols now need to be tested in prospective multicentre trials to confirm their performance in prospective practice.