Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Objective: To identify clinical and genetic risk factors for moderate hyperbilirubinemia during the first week of life. Study Design: Using univariate and multivariate multiple regression analyses, the RR for clinical factors, the African variant of glucose-6-phosphate dehydrogenase (G6PD) deficiency (G202A/A376G), and (TA)(n) UGT1A1 polymorphisms were established in a cohort of 608 Brazilian newborn infants. Hyperbilirubinemia was monitored until 134.5 +/- 49.8 h of life (IQR, 111.0 to 156.7). The dependent variable was total bilirubinemia (TB) >= 12.9 mg per 100 ml estimated by transcutaneous or plasma bilirubin measurements. Result: The African variant of G6PD deficiency and (TA)(7)/(TA)(7) and (TA)(7)/(TA)(8) polymorphisms present in 6.1 and 12.0% of newborns, respectively, were not risk factors for moderate hyperbilirubinemia. Coexpression of G6DP deficiency and UGT1A1 polymorphisms occurred in 0.49% of the subjects. Independent clinical predictors for TB >= 12.9mg per 100 ml were gestational age <38 weeks and reference curve percentiles >P40th. Conclusion: In this study, G6PD deficiency and UGT1A1 gene promoter polymorphisms were not risk factors for moderate hyperbilirubinemia. Genetic factors may vary considerably in importance among different populations. Journal of Perinatology (2010) 30, 819-826; doi: 10.1038/jp.2010.48; published online 8 April 20103012819826Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2006/60917-1]