OBJECTIVES: Pregnancies with Edwards or Patau syndrome are often detected 
through screening for Down's syndrome. We aimed to evaluate the impact of 
screening for Down's syndrome on the prevalence of live births and antenatal 
diagnoses of Edwards and Patau syndrome.
SETTING: England and Wales, 2005 to 2012.
METHODS: Data from the National Down Syndrome Cytogenetic Register, which 
contains information on nearly all ante- or postnatally diagnosed cases of 
Edwards or Patau syndrome in which a karyotype was confirmed, were analysed.
RESULTS: From 2005 to 2012, 3,941 diagnoses of Edwards syndrome and 1,567 
diagnoses of Patau syndrome were recorded (prevalence of 7.0 and 2.8 per 10,000 
births respectively). Only 11% (95% confidence interval [CI]: 10-12) of 
diagnoses of Edwards syndrome and 13% (95% CI: 11-14) of Patau syndrome were 
live births, resulting in live birth prevalences of 0.8 (95% CI: 0.7-0.8) and 
0.4 (95% CI: 0.3-0.4) per 10,000 live births respectively. About 90% of 
pregnancies with Edwards or Patau syndrome were diagnosed antenatally, and this 
proportion remained constant over time. The proportion of diagnoses detected 
before 15 weeks increased from 50% in 2005 to 53% in 2012 for Edwards syndrome, 
and from 41% in 2005 to 63% in 2012 for Patau syndrome.
CONCLUSIONS: Almost 700 women per year had a pregnancy with Edwards or Patau 
syndrome. Over 90% of these pregnancies were detected antenatally, with the 
increased use of first trimester screening for Down's syndrome resulting in the 
reduction in the mean gestational age at diagnosis of these syndromes.