Zdravniški Vestnik (Oct 2014)
Analysis of Second Trimester Maternal Quadruple Screening Test for Trisomy 21 and Trisomy 18
Abstract
Background: The second trimester quadruple screening test for foetal chromosomal abnormalities has been carried out in Slovenia since 2006. Our objective was to analyse the quadruple test results, define sensibility and specificity, the positive and negative predictive value of the screening test for trisomy 21 and trisomy 18 and the influence of some maternal clinical parameters on risk calculation. Methods: Retrospectively collected results of 3,719 maternal blood samples were analysed in the period from February 1st, 2006 to December 31st, 2009 at the University Medical Centre Ljubljana. We obtained information on maternal age, body weight and smoking (habits?), karyotyping of foetuses and clinical data on newborns.Results: The sensitivity of the test for trisomy 21 was 50%, specificity 95%, positive predictive value 2.3% and negative predictive value 99.8%. Specificity for trisomy 18 was 98%, sensitivity 100% and the positive and negative predictive value 1.4% and 100% respectively.. False positive results in trisomy 21 were influenced by maternal weight (OR=1.034; p=0.00) and age (OR=0.832; p=0.00). It was influenced by maternal age (OR=0.924; p=0.17) and smoking (OR=0.396; p=0.006) in the case of trisomy 18.Conclusions: A quadruple test has an appropriate specificity for detecting foetuses with trisomy 21; however, it displays a low sensibility as well as a low positive predictive value. The test reveals high specificity and sensibility for the detection of foetal trisomy 18, and has a high negative predictive value, yet its positive predictive value remains low. Therefore, the test is primarily intended for pregnant women who, for various reasons, missed out on screening opportunities in the first trimester of their pregnancy.
