title: Applying measures of discriminatory accuracy to revisit traditional risk factors for being small for gestational age in Sweden: a national cross-sectional study.
abstract: OBJECTIVE
  Small for gestational age (SGA) is considered as an indicator of intrauterine growth restriction, and multiple maternal and newborn characteristics have been identified as risk factors for SGA. This knowledge is mainly based on measures of average association (ie, OR) that quantify differences in average risk between exposed and unexposed groups. Nevertheless, average associations do not assess the discriminatory accuracy of the risk factors (ie, its ability to discriminate the babies who will develop SGA from those that will not). Therefore, applying measures of discriminatory accuracy rather than measures of association only, our study revisits known risk factors of SGA and discusses their role from a public health perspective.
  
  
  METHODS
  Cross-sectional study. We measured maternal (ie, smoking, hypertension, age, marital status, education) and delivery (ie, sex, gestational age, birth order) characteristics and performed logistic regression models to estimate both ORs and measures of discriminatory accuracy, like the area under the receiver operating characteristic curve (AU-ROC) and the net reclassification improvement.
  
  
  METHODS
  Data were obtained from the Swedish Medical Birth Registry.
  
  
  METHODS
  Our sample included 731 989 babies born during 1987-1993.
  
  
  RESULTS
  We replicated the expected associations. For instance, smoking (OR=2.57), having had a previous SGA baby (OR=5.48) and hypertension (OR=4.02) were strongly associated with SGA. However, they show a very small discriminatory accuracy (AU-ROC≈0.5). The discriminatory accuracy increased, but remained unsatisfactorily low (AU-ROC=0.6), when including all variables studied in the same model.
  
  
  CONCLUSIONS
  Traditional risk factors for SGA alone or in combination have a low accuracy for discriminating babies with SGA from those without SGA. A proper understanding of these findings is of fundamental relevance to address future research and to design policymaking recommendations in a more informed way.
authors: Center for Economic Demography, Lund University, Sweden Department of Clinical Sciences, Unit of Social Epidemiology, Lund University, Malmö, Skåne University Hospital (SUS Malmö), Malmö, Sweden.
authors: Sol Pía
authors: SP
authors: Juárez
authors: Department of Clinical Sciences, Unit of Social Epidemiology, Lund University, Malmö, Skåne University Hospital (SUS Malmö), Malmö, Sweden.
authors: Phillip
authors: P
authors: Wagner
authors: Department of Clinical Sciences, Unit of Social Epidemiology, Lund University, Malmö, Skåne University Hospital (SUS Malmö), Malmö, Sweden.
authors: Juan
authors: J
authors: Merlo
mesh_terms: D000367:Age Factors; D019540:Area Under Curve; D003430:Cross-Sectional Studies; D004522:Educational Status; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D007223:Infant; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age / Q000502:physiology; D016015:Logistic Models; D008297:Male; D017533:Marital Status; D011247:Pregnancy; D011248:Pregnancy Complications; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects; D013548:Sweden / Q000453:epidemiology