title: The epidemiology of mental retardation of unknown cause.
abstract: OBJECTIVE
  To describe selected infant and maternal characteristics for children with mild and severe mental retardation (MR) of unknown cause.
  
  
  METHODS
  Children with MR of unknown cause born in California between 1987 and 1994 were identified through service agency records and compared with the total population of California live births for selected characteristics recorded on the birth certificate.
  
  
  RESULTS
  For both children with mild and severe MR, risk was increased among males, low birth weight children, and children born to women of black race, older age at delivery, and lower level of education. Increased risk for mild MR was found for multiple births, second or later-born children, and children whose mothers were born outside of California. Increased risk for severe MR was observed among children born to Hispanic mothers; children born to Asian mothers also had increased risk for severe MR but decreased risk for mild MR.
  
  
  CONCLUSIONS
  These results provide clues for understanding the underlying causes of MR and suggest that both biological and social factors are important.
authors.affiliation: March of Dimes Birth Defects Foundation, California Department of Health Services, California Birth Defects Monitoring Program, Oakland, California, USA. lac@dor.kaiser.org
authors.forename: L A
authors.initials: LA
authors.lastname: Croen
authors.forename: J K
authors.initials: JK
authors.lastname: Grether
authors.forename: S
authors.initials: S
authors.lastname: Selvin
mesh_terms: D000293:Adolescent; D000328:Adult; D001719:Birth Certificates; D001722:Birth Order; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D004522:Educational Status; D005260:Female; D006801:Humans; D007223:Infant; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008607:Intellectual Disability / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008423:Maternal Age; D009099:Multiple Birth Offspring / Q000706:statistics & numerical data; D011247:Pregnancy; D015995:Prevalence; D044469:Racial Groups; D012307:Risk Factors; D012720:Severity of Illness Index; D012737:Sex Factors