Cycled light in the intensive care unit for preterm and low birth weight infants

The pregnant woman is exposed to variable intensities of lighting and sound and, in general, lower levels at night. Some of the lighting and sound reaches the fetus in the womb and induces circadian rhythms. Circadian is a term used to describe biological processes that recur naturally on a 24-hour basis. After birth, preterm infants are cared for in an environment that has no planned light-dark cycles or any other circadian entraining signals. Infants are exposed to either continuous bright light, continuous near darkness or an unstructured combination of the two. Our primary objective was to determine the effectiveness of cycled light (approximately 12 hours of light on and 12 hours of light off) on growth in preterm infants at three and six months corrected gestational age. To date fewer than 500 infants have been enrolled in trials assessing the effect of cycled light. One study reported improved growth at three months of age. One study found no difference in weight at four months of age. Only few outcomes reached statistical significance, likely due to the small number of infants enrolled in the studies, but trends for most outcomes (weight gain, length of stay, incidence of retinopathy of prematurity) favoured cycled light compared to near darkness and cycled light compared to continuous bright light.