Eligible cases with congenital heart defect for this study were live births and stillbirths with isolated or multiple congenital heart defects. Three clinical diagnostic groups of isolated cardiac defects and one group of multiple cardiac defects were defined as: (1) atrial and atrial septal defects (N¼567;codes:Q24.2, Q26.2,Q21.1); (2) ventricular septal defect excluded from the conotruncal category (N¼526;codes:Q21.0,Q21,Q21.2); (3) new borns with patent ductus arteriosus with birth weight 42500g(N¼167,code:Q25.0); and (4) multiple congenital heart defects, defined by the presence of two or more cardiac malformations (N¼607,codes:Q20–Q28). Syndromic cases with geneticor or Chromosomal malformations were excluded from the analyses. Congenital heart defects in combination with malformations in other organ systems were also excluded from analyses.