title: Distribution of maternal age and birth order groups in cases with unclassified multiple congenital abnormalities according to the number of component abnormalities: a national population-based case-control study.
abstract: BACKGROUND
  Multiple congenital abnormalities are caused by chromosomal aberrations, mutant major genes and teratogens. A minor proportion of these patients are identified as syndromes but the major part belonging to the group of unclassified multiple CAs (UMCAs). The main objective of this study was to evaluate the maternal age and birth order in pregnant women who had offspring affected with UMCA. The strong association between numerical chromosomal aberrations, e.g., Down syndrome and advanced maternal age is well-known and tested here.
  
  
  METHODS
  The Hungarian Case-Control Surveillance of Congenital Abnormalities, 1980 to 1996, yielded a large population-based national data set with 22,843 malformed newborns or fetuses ("informative cases") included 1349 UMCA cases with their 2407 matched controls. Case-control comparison of maternal age and birth order was made for cases with UMCA, stratified by component numbers and their controls. In addition, 834 cases with Down syndrome were compared to 1432 matched controls.
  
  
  RESULTS
  The well-known advanced maternal age with the higher risk for Down syndrome was confirmed. The findings of the study suggest that the young age of mothers associates with the higher risk of UMCA, in addition birth order 4 or more associates with the higher risk for UMCA with 2 and 3 component CAs.
  
  
  CONCLUSIONS
  This study was the first to analyze the possible maternal and birth order effect for cases with UMCA, and the young age and higher birth order associated with a higher risk for UMCA.
authors.affiliation: RMC Fetal Medicine Center, Budapest, Hungary.
authors.forename: Gyula
authors.initials: G
authors.lastname: Csermely
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Czeizel
authors.forename: Béla
authors.initials: B
authors.lastname: Veszprémi
mesh_terms: D000015:Abnormalities, Multiple / Q000453:epidemiology* / Q000235:genetics / Q000473:pathology; D000328:Adult; D000367:Age Factors; D001722:Birth Order; D016022:Case-Control Studies; D004314:Down Syndrome / Q000453:epidemiology* / Q000235:genetics / Q000473:pathology; D062665:Epidemiological Monitoring; D005260:Female; D006801:Humans; D006814:Hungary / Q000453:epidemiology; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D009035:Mothers; D011247:Pregnancy; D012042:Registries; D012306:Risk
keywords: Down syndrome; birth order; maternal age; multiple congenital abnormalities; population-based case-control study; unclassified multiple congenital abnormalities