title: Reliability of statistics on Down's syndrome notifications.
abstract: OBJECTIVE
  To evaluate the completeness of notifications of Down's syndrome live births and terminations to the Office for National Statistics (ONS) using data from the National Down Syndrome Cytogenetic Register (NDSCR). To examine the agreement of observed birth prevalence of Down's syndrome with the expected birth prevalence derived from published maternal age specific rates.
  
  
  METHODS
  The number of live births (adjusted to allow for the estimated underascertainment) and the number of terminations due to fetal Down's syndrome from NDSCR were compared with those figures reported to the ONS. Subsequently, using the NDSCR figures, the live birth prevalence of Down's syndrome that would have occurred in the absence of antenatal diagnosis and selective termination was calculated in England and Wales in the years 1990-1993. These figures were compared with those derived by applying published age specific prevalences to the maternal age distribution in England and Wales.
  
  
  RESULTS
  It is estimated that only 48% and 46% respectively of Down's syndrome live births and terminations of pregnancy were notified to ONS between 1990 and 1993. The annual expected birth prevalences of Down's syndrome obtained by applying maternal age specific prevalences to the maternal age distribution were in close agreement with observed rates from NDSCR.
  
  
  CONCLUSIONS
  There is considerable underreporting of Down's syndrome births and terminations to ONS. The NDSCR data are more complete and therefore the effects of screening should be monitored using data from this source, or using estimates derived from the age specific rates of Down's syndrome.
authors.affiliation: Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, St Bartholomew's and the Royal London School of Medicine and Dentistry, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Huang
authors.forename: H C
authors.initials: HC
authors.lastname: Watt
authors.forename: N J
authors.initials: NJ
authors.lastname: Wald
authors.forename: J K
authors.initials: JK
authors.lastname: Morris
authors.forename: D
authors.initials: D
authors.lastname: Mutton
authors.forename: E
authors.initials: E
authors.lastname: Alberman
mesh_terms: D000028:Abortion, Induced / Q000706:statistics & numerical data; D017677:Age Distribution; D001723:Birth Rate; D004314:Down Syndrome / Q000453:epidemiology* / Q000235:genetics; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D015233:Models, Statistical; D009313:National Health Programs / Q000706:statistics & numerical data*; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000706:statistics & numerical data; D014852:Wales / Q000453:epidemiology