Definitions Commenced screening At one of the required components of the screening test was completed. Completed screening All the required components of each screening test were complete and a risk result was calculated. Required components of each screening test First trimester screening comprises analysis of two serum analytes (βhCG, PAPP-A) and a NT measurement. Second trimester screening comprises analysis of four serum analytes (βhCG, AFP, uE3 and Inhibin A). Low risk result A low risk result is defined as a risk lower than 1:300. So a risk of 1:310 is a low risk. Increased risk result An increased risk result is defined as a risk higher than or equal to 1:300. For some indicators increased risk screening results are further stratified into: 1:5 to 1:20 1:25 to 1:50 1:55 to 1:300. Inclusion criteria Women’s screens were included in this analysis if the following criteria were met: screening commencement date between 1 January 2011 and 31 December 2015 (ie, date of the first test the woman had as part of the screening pathway) valid National Health Index identifier (NHI) known District Health Board (DHB) of domicile age at screen from 12 to 49 years (calculated using the NHI database date of birth) single screening result per pregnancy. Data calculations DHB of domicile Each woman was allocated to a DHB based on the residential address recorded in the National Health Index (NHI). Where the NHI database did not have a DHB recorded for an NHI, information from the LabPLUS database was used to assign the DHB.
Table 22: Increased risk screening results for trisomy 21, 18 and 13 by trimester of screen, January 2011 to December 2015 Year Total increased risks for specified trisomy Positive test rate per 100 screens T1 results with increased risk for specified trisomy Positive test rate per 100 T1 screens T2 results with increased risk for specified trisomy Positive test rate per 100 T2 screens Trisomy 21 2011 1,081 2.8 868 2.5 213 4.8 2012 1,144 2.8 871 2.4 273 5.5 2013 1,081 2.7 840 2.4 241 4.6 2014 1,131 2.7 870 2.4 261 4.8 2015 1,140 2.7 937 2.6 203 3.7 Trisomy 18 2011 134 0.3 123 0.4 11 0.2 2012 161 0.4 149 0.4 12 0.2 2013 145 0.4 125 0.4 20 0.4 2014 136 0.3 120 0.3 16 0.3 2015 145 0.3 127 0.3 18 0.3 Trisomy 13 2011 143 0.4 140 0.4 3 0.1 2012 169 0.4 161 0.5 8 0.2 2013 158 0.4 144 0.4 14 0.3 2014 149 0.4 135 0.4 14 0.3 2015 159 0.4 147 0.4 12 0.2 Any one or more of trisomy 21, 18 or 13 2011 1,099 2.8 878 2.5 221 5.0 2012 1,156 2.8 874 2.4 282 5.7 2013 1,103 2.7 847 2.4 256 4.9 2014 1,157 2.8 883 2.4 274 5.0 2015 1,163 2.8 942 2.6 221 4.0
Indicator 8: Diagnostic testing for unscreened women This section reports information on the number of women who completed prenatal diagnostic testing but were not screened in the 105 days prior to the diagnostic test. The indication for diagnostic testing is not reliably reported on laboratory request forms but it is likely that many of these women will have had an increased prior risk (eg, family history, previous child with Down syndrome, late maternal age) or a diagnostic test done for another reason and the karyotype reported or an abnormal ultrasound finding. Diagnostic volumes for unscreened women During the 2015 year, 252 diagnostic tests were completed for unscreened women. This is similar to the number undertaken in previous years. Table 32 shows the number of tests by DHB and Table 33 shows the breakdown by age, ethnicity and NZ deprivation quintile. Table 32: Diagnostic testing volumes for unscreened women by DHB, January 2012 to December 2015 DHB Number of diagnostic tests 2012 2013 2014 2015 Northland 10 6 7 8 Waitemata 37 24 22 22 Auckland 31 23 25 18 Counties Manukau 19 27 21 18 Waikato 16 24 14 15 Lakes 2 5 6 8 Bay of Plenty 10 18 12 14 Tairawhiti 5 - 1 3 Hawke’s Bay 11 6 7 7 Taranaki 13 11 5 11 MidCentral 9 11 11 8 Whanganui 4 2 3 2 Capital and 17 16 30 36 Hutt Valley 9 11 11 22 Wairarapa 5 1 1 3 Nelson Marlborough 7 1 4 6 West Coast - 1 1 - Canterbury 27 23 37 30 South Canterbury - 2 4 2 Southern 17 18 13 19 Total 249 203 235 252
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.
50: Detection rate for trisomy 21, January 2011 to December 2015 Year True positives False negatives Detection rate 2011 88 25 0.78 2012 95 27 0.78 2013 109 26 0.81 2014 89 18 0.83 2015 95 12 0.89 Table 51: Detection rate for trisomy 13 or 18, January 2011 to December 2015 Year True positives negatives Detection rate 2011 43 16 0.73 2012 38 21 0.64 2013 28 17 0.62 2014 27 15 0.64 2015 30 8 0.79 Detection rate for screening for trisomy 21 by age, ethnicity and deprivation Due to the low number of true positives and false negative results for some groups the detection rates for trisomy 21 have been calculated in aggregate across the five years in order to present more stable rates. Numbers for the youngest and oldest age groups are still very low after aggregation so care should be taken with interpretation of these. Across the other age groups the detection rate for trisomy 21 appears to increase with age from 0.59 (59%) for women 20–24 years to 0.95 (95%) for women 40-44 years (see Table 52). 52: Detection rate for trisomy 21 by age, aggregated 2011 – 2015 Age True positives False negatives Detection rate# Positive diagnostic test/ infant diagnosis increased risk screen Positive diagnostic test/ infant diagnosis low risk screen Under 20 years 3 5 - 20–24 years 13 9 0.59 25–29 years 33 15 0.69 30–34 years 91 40 0.69 35–39 years 195 32 0.86 40–44 135 7 0.95 45 and over 6 0 - # Rate suppressed if the number of positive diagnoses was <10.
Appendix 7: Radiology indicator summary measures Bias – the bias is the difference between observed NT measurements and we would expect from the FMF curve. For example, the expected NT measurement for a CRL of 60mm is 1.65mm. If a fetus with a CRL measurement of 60mm has an NT measurement of 2mm, the difference is 0.35mm 2mm – 1.65mm = 0.35mm Or if the measured NT is 1mm, the difference is -0.65mm 1mm – 1.65mm = ‐0.65mm The figures shown in the distribution plot are the number and percentage of measurements above and below the FMF curve. Spread – the spread of NT measurements is the way most measurements will cluster the FMF curve. The number shown is the factor by which the spread is increased (the measurements vary more greatly than would be expected given the CRL) or decreased (the measurements cluster very tightly around the curve, without the expected normal variance). Trend – the curve of observed NT /CRL values should mimic the FMF curve in shape and direction. The value displayed shows the degree of discrepancy between the expected trend and the observed measurements.