2013 139 964 0.13 2014 121 1,036 0.10 2015 126 1,037 0.11 The PPV changes when calculated for a specific trisomy. When looking at trisomy 21 the PPV for 2015 was lower than the combined PPV at 0.08 (see Table 36). This means that if a woman receives an increased risk result for trisomy 21 there is an 8% probability that she is carrying a fetus with trisomy 21. Table 36: Positive predictive of screening for trisomy 21, January 2011 to December 2015 Year True positives False positives PPV 2011 993 0.08 88 2012 95 1,049 0.08 109 972 0.10 2013 89 1,042 0.08 2014 2015 95 1,045 0.08 Trisomies 13 and 18 involve small numbers and have similar risk profiles so combined results for PPV and the remaining indicators have been calculated for these trisomies. The combined PPV for trisomies 13 or 18 for 2015 was higher than the trisomy 21 PPV at 0.17 (see Table 37). However, the number of positive diagnoses for these two trisomies is low so caution should be taken when interpreting these results. 37: Positive predictive of screening for trisomy 13 or 18, January 2011 to December 2015 Year True positives False positives PPV 2011 43 127 0.25 38 148 0.20 2012 28 150 0.16 2013 2014 27 144 0.16 2015 30 149 0.17 Positive predictive value of screening for trisomy 21 stratified by risk level Table 38 shows PPV stratified by the risk level indicated in the screening result. Data have been aggregated across the 2011 to 2015 period. Women that received a very increased risk result of 1:5 to 1:20 for trisomy 21 had a 27% probability that they were carrying a fetus with trisomy 21.
2013 139 964 0.13 2014 121 1,036 0.10 2015 126 1,037 0.11 The PPV changes when calculated for a specific trisomy. When looking at trisomy 21 the PPV for 2015 was lower than the combined PPV at 0.08 (see Table 36). This means that if a woman receives an increased risk result for trisomy 21 there is an 8% probability that she is carrying a fetus with trisomy 21. Table 36: Positive predictive of screening for trisomy 21, January 2011 to December 2015 Year True positives False positives PPV 2011 88 993 0.08 2012 95 1,049 0.08 2013 109 972 0.10 2014 89 1,042 0.08 2015 95 1,045 0.08 Trisomies 13 and 18 involve small numbers and have similar risk profiles so combined results for PPV and the remaining indicators have been calculated for these trisomies. The combined PPV for trisomies 13 or 18 for 2015 was higher than the trisomy 21 PPV at 0.17 (see Table 37). However, the number of positive diagnoses for these two trisomies is low so caution should be taken when interpreting these results. 37: Positive predictive of screening for trisomy 13 or 18, January 2011 to December 2015 Year True positives False positives PPV 2011 43 127 0.25 2012 38 148 0.20 2013 28 150 0.16 2014 27 144 0.16 2015 30 149 0.17 Positive predictive value of screening for trisomy 21 stratified by risk level Table 38 shows PPV stratified by the risk level indicated in the screening result. Data have been aggregated across the 2011 to 2015 period. Women that received a very increased risk result of 1:5 to 1:20 for trisomy 21 had a 27% probability that they were carrying a fetus with trisomy 21.
antenatal-screening-down-syndrome-other-conditions-monitoring-jan2011-dec2015-may17.docx