title: The maternal age-specific live birth prevalence of trisomies 13 and 18 compared to trisomy 21 (Down syndrome).
abstract: OBJECTIVE
  To estimate the maternal age-specific live birth prevalence (in the absence of prenatal diagnosis and selective termination) of trisomy 13 (Patau syndrome) and trisomy 18 (Edwards syndrome) and compare it with that of trisomy 21 (Down syndrome).
  
  
  METHODS
  Records of prenatal and postnatal diagnoses from seven UK regional congenital anomaly registers and two Australian registers covering 4.5 million births included 975 diagnoses of trisomy 13 and 2254 of trisomy 18. Prevalence at birth in the absence of prenatal diagnosis and selective termination was calculated by adjusting for prenatally diagnosed pregnancies that were terminated according to their likelihood of surviving to term.
  
  
  RESULTS
  The live birth prevalence in the absence of prenatal screening and selective termination in England and Wales from 1997 to 2004 was 1.4 (95% CI: 1.2-1.6) per 10 000 births for trisomy 13 and 2.3 (95% CI: 2.1-2.5) for trisomy 18. It has increased since 1989-1996, by 13% for trisomy 13 and 25% for trisomy 18. These increases are consistent with those predicted due to increases in maternal age.
  
  
  CONCLUSIONS
  This study provides the first estimates of maternal age-specific prevalence of trisomies 13 and 18 for women aged 16-45.
authors.affiliation: Department of Public Health and Primary Care, University of Cambridge, Institute of Public Health, Cambridge, UK.
authors.forename: George M
authors.initials: GM
authors.lastname: Savva
authors.forename: Kate
authors.initials: K
authors.lastname: Walker
authors.forename: Joan K
authors.initials: JK
authors.lastname: Morris
mesh_terms: D000293:Adolescent; D000328:Adult; D001315:Australia / Q000453:epidemiology; D002882:Chromosomes, Human, Pair 13; D002887:Chromosomes, Human, Pair 18; D004314:Down Syndrome / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D005260:Female; D006801:Humans; D050498:Live Birth / Q000453:epidemiology*; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D015995:Prevalence; D012042:Registries; D014314:Trisomy / Q000175:diagnosis / Q000235:genetics*; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult