The population impact of screening for Down syndrome: audit of 19 326 invasive diagnostic tests in England and Wales in 2008

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Abstract
Objective Pregnant women who receive a high screening risk result for Down, Edwards or Patau syndrome are offered diagnostic tests that carry a risk of miscarriage. This study determined how many women had such tests per syndrome diagnosis. Method The number of tests per Down, Edwards or Patau syndrome diagnosis adjusted for maternal and gestational age at diagnosis was calculated using routine data from 18 (95%) cytogenetic laboratories in England and Wales in 2008. Results There were 19 326 tests that identified 1118 diagnoses of Down syndrome and 615 of Edwards and Patau syndromes. There were eight chorionic villus samplings (CVS) per syndrome diagnosis compared with 16 amniocenteses (gestational age adjusted). The lowest number of tests per diagnosis (three for CVSs and for amniocentesis) resulted from an abnormal ultrasound scan. Among pregnant women, 2.9% had an invasive diagnostic test. If a CVS and an amniocentesis increase the risk of a miscarriage by 1% and 0.5%, respectively, approximately one miscarriage for every 14 Down, Edwards or Patau syndrome diagnosis would have occurred. Conclusion A simple measurement of the population impact of screening for Down syndrome can be calculated using data already collected. Annual estimates should be produced to monitor the national fetal anomaly screening programme. © 2012 John Wiley & Sons, Ltd.