title: Possible association of first and high birth order of pregnant women with the risk of isolated congenital abnormalities in Hungary - a population-based case-matched control study.
abstract: OBJECTIVE
  In epidemiological studies at the estimation of risk factors in the origin of specified congenital abnormalities in general birth order (parity) is considered as confounder. The aim of this study was to analyze the possible association of first and high (four or more) birth order with the risk of congenital abnormalities in a population-based case-matched control data set.
  
  
  METHODS
  The large dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities included 21,494 cases with different isolated congenital abnormality and their 34,311 matched controls. First the distribution of birth order was compared of 24 congenital abnormality groups and their matched controls. In the second step the possible association of first and high birth order with the risk of congenital abnormalities was estimated. Finally some subgroups of neural-tube defects, congenital heart defects and abdominal wall's defects were evaluated separately.
  
  
  RESULTS
  A higher risk of spina bifida aperta/cystica, esophageal atresia/stenosis and clubfoot was observed in the offspring of primiparous mothers. Of 24 congenital abnormality groups, 14 had mothers with larger proportion of high birth order. Ear defects, congenital heart defects, cleft lip± palate and obstructive defects of urinary tract had a linear trend from a lower proportion of first born cases to the larger proportion of high birth order. Birth order showed U-shaped distribution of neural-tube defects and clubfoot, i.e. both first and high birth order had a larger proportion in cases than in their matched controls.
  
  
  CONCLUSIONS
  Birth order is a contributing factor in the origin of some isolated congenital abnormalities. The higher risk of certain congenital abnormalities in pregnant women with first or high birth order is worth considering in the clinical practice, e.g. ultrasound scanning.
authors: Rozsakert Medical Center Fetal Medicine Clinic, Gábor Áron út 74-78, H-1026 Budapest, Hungary. Electronic address: csermelyphone@gmail.com.
authors: Gyula
authors: G
authors: Csermely
authors: Semmelweis University, Institute of Behavioural Sciences, Budapest, Hungary.
authors: Éva
authors: É
authors: Susánszky
authors: Foundation for the Community Control of Hereditary Diseases, Budapest, Hungary.
authors: Andrew E
authors: AE
authors: Czeizel
authors: Department of Obstetrics and Gynecology, University of Pécs, Pécs, Hungary.
authors: Béla
authors: B
authors: Veszprémi
mesh_terms: D000328:Adult; D001722:Birth Order; D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000453:epidemiology*; D005260:Female; D006801:Humans; D006814:Hungary / Q000453:epidemiology; D010298:Parity; D011159:Population Surveillance; D011247:Pregnancy; D012042:Registries; D012306:Risk
keywords: Birth order; Congenital abnormalities; High birth order; Population-based case-control study; Primiparious