Effect of seasonal variation in daylight on bilirubin level in premature infants.

The effect of daylight on the serum bilirubin level of preterm infants (birthweight less than 2500 g) during the first 10 days of life was studied in a district of Finland (Oulu, latitude 65 degrees ĺ) with large seasonal variations in the length of daylight (range 3 to 22 h). 86 preterm infants born consecutively during one calendar year were studied in incubators where they were completely exposed except for nappies. A significantly lower bilirubin value from the fifth day of life onwards was recorded ih the group of infants born during the light half of the year, compared with the infants born during the dark half of the year. Only 4 infants developed total bilirubin levels higher than 255 mumol/l in the "light group", as compared with 10 in the "dark group". 2 infants in the light group required exchange transfusion, while 4 in the dark group did. It is concluded than natural light conditions are of importance in the design of wards for newborn infants.