title: Mediation analysis of gestational age, congenital heart defects, and infant birth-weight.
abstract: BACKGROUND
  In this study we assessed the mediation role of the gestational age on the effect of the infant's congenital heart defects (CHD) on birth-weight.
  
  
  METHODS
  We used secondary data from the Baltimore-Washington Infant Study (1981-1989). Mediation analysis was employed to investigate whether gestational age acted as a mediator of the association between CHD and reduced birth-weight. We estimated the mediated effect, the mediation proportion, and their corresponding 95% confidence intervals (CI) using several methods.
  
  
  RESULTS
  There were 3362 CHD cases and 3564 controls in the dataset with mean birth-weight of 3071 (SD = 729) and 3353 (SD = 603) grams, respectively; the mean gestational age was 38.9 (SD = 2.7) and 39.6 (SD = 2.2) weeks, respectively. After adjusting for covariates, the estimated mediated effect by gestational age was 113.5 grams (95% CI, 92.4-134.2) and the mediation proportion was 40.7% (95% CI, 34.7%-46.6%), using the bootstrap approach.
  
  
  CONCLUSIONS
  Gestational age may account for about 41% of the overall effect of heart defects on reduced infant birth-weight. Improved prenatal care and other public health efforts that promote full term delivery, particularly targeting high-risk families and mothers known to be carrying a fetus with CHD, may therefore be expected to improve the birth-weight of these infants and their long term health.
authors.forename: Adane F
authors.initials: AF
authors.lastname: Wogu
authors.affiliation: Departments of Oncology and of Biostatistics, Bioinformatics, and Biomathematics, Georgetown University, 3800 Reservoir Rd, NW, Washington, DC 20057, USA. cal9@georgetown.edu.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Loffredo
authors.forename: Ionut
authors.initials: I
authors.lastname: Bebu
authors.forename: George
authors.initials: G
authors.lastname: Luta
mesh_terms: D000328:Adult; D001724:Birth Weight; D016022:Case-Control Studies; D004219:District of Columbia / Q000453:epidemiology; D004522:Educational Status; D005260:Female; D005865:Gestational Age; D006330:Heart Defects, Congenital / Q000453:epidemiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008396:Maryland / Q000453:epidemiology; D008423:Maternal Age; D009035:Mothers; D018570:Risk Assessment / Q000379:methods / Q000706:statistics & numerical data*; D012307:Risk Factors; D012907:Smoking; D014768:Virginia / Q000453:epidemiology