title: Familial aggregation of small-for-gestational-age births: the importance of fetal genetic effects.
abstract: OBJECTIVE
  This study was undertaken to disentangle the maternal genetic, fetal genetic, and environmental effects for the risk of having small-for-gestational-age (SGA) offspring.
  
  
  METHODS
  By cross-linking the population-based Swedish Multi-Generation and Medical Birth Registers, we extracted 2,193,142 births between 1973 and 2001 with both parents identified. Odds ratios (OR) were calculated to estimate the relative risks, and generalized linear mixed models were used to estimate the contribution of genetic and environmental effects.
  
  
  RESULTS
  Women whose full sisters had an offspring born SGA had a significantly increased risk of having a SGA offspring themselves (OR = 1.8, 95% CI 1.7-1.9), whereas the corresponding risk for brothers was lower (OR = 1.3, 95% CI 1.2-1.4). Thirty-seven percent of the liability was explained by fetal (including both maternal and paternal) genetic effects and 9% by maternal genetic effects.
  
  
  CONCLUSIONS
  Genetic factors account for almost half of the liability to have SGA births. These effects are primarily caused by fetal genes.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. Anna.Svensson@meb.ki.se
authors.forename: Anna C
authors.initials: AC
authors.lastname: Svensson
authors.forename: Yudi
authors.initials: Y
authors.lastname: Pawitan
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
authors.forename: Marie
authors.initials: M
authors.lastname: Reilly
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
mesh_terms: D005260:Female; D005317:Fetal Growth Retardation / Q000235:genetics*; D005333:Fetus / Q000503:physiopathology*; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D016014:Linear Models; D016017:Odds Ratio; D011247:Pregnancy; D012042:Registries; D012307:Risk Factors; D035781:Siblings; D012907:Smoking / Q000453:epidemiology; D013548:Sweden / Q000453:epidemiology; D014599:Uterus / Q000503:physiopathology