Effects of season of birth and meteorological parameters on serum bilirubin levels during the early neonatal period: a retrospective chart review

Abstract Background: Neonatal jaundice can be influenced by many factors. Several studies have suggested that the severity of neonatal jaundice may vary with the season, but conclusive data on this issue are currently lacking. The aim of the present study was to establish whether serum bilirubin levels vary in healthy term neonates according to seasonal variation and meteorological factors.Methods: We retrospectively studied 3,344 healthy term neonates born between 2013 and 2018. Using the capillary technique, total serum bilirubin (TSB) levels were measured on the fourth day after birth. The monthly and seasonal variations in TSB levels and clinical and meteorological effects on TSB levels were assessed.Results: In the enrolled neonates, the median gestational age was 39.4 weeks, median birthweight was 3,025 g, and median TSB level was 195 µmol/L. The TSB level peaked in December and was the lowest in July, but the variation was not statistically significant. The TSB level was significantly higher in the cold season (October to March) than in the warm season (April to September; p=0.01). Comparing the seasonal differences according to sex, TSB levels were significantly higher in the cold season in male infants (p=0.001), whereas no significant difference was observed in female infants. In only the male population did a weakly negative but significant association exist between TSB levels and daily mean air temperature (r=-0.07, p=0.007); in the female population, no significant correlation was found between TSB levels and meteorological parameters.Conclusions: Season of birth appears to be an etiological factor in neonatal jaundice, with an additional influence of sex. However, the contradictions observed in various studies highlight the need for further research on this topic.