The neonatal intensive care unit environment cannot possibly replicate the womb for all preterm infants.  The purpose of this study was to evaluate the effects of cycled light versus near darkness on health and growth of preterm infants.  The study was set up as a randomized interventional study comparing infants receiving cycled light from birth, cycled light at 32 weeks post-conceptional age, and cycled light at 36 weeks of post-conceptional age.  Infants receiving cycled light at birth and at 32 weeks post-conceptional age gained weight faster than infants not receiving cycled light until 36 weeks (Figure 1).  There was no difference among the groups in length of hospitalization stay, or number of ventilator days, but the power was low for these variables.  The authors concluded that cycled light had significant weight gain benefits over near darkness in preterm infants.

Editor’s Comment: The findings of this study confirm the observations of others who reported that cycled light from birth or beginning at 32 weeks post-conception positively influenced weight gain in preterm infants.  The positive effects of weight gain in preterm infants were first reported by Mann et al BMJ 1986;293:1265-7.  However, there have been other reports that suggested that continued bright light is detrimental to the health of preterm infants (J Perinat Neonat Nurs 1991;4:47-54 and Infant Behav Dev 1995;18:87-95).  Since near-darkness has become the standard of care in nurseries, these findings are important.  The presence of significant circadian rhythms provided by maternal cycles even while the fetus is in the intrauterine environment suggest that replicating them after birth may be of benefit.  Growth, Genetics and Hormones published an excellent review of circadian rhythms written by Dr. Rivkees in Vol 18, No.1, 2002. 

Cycled light could be important for human development, in addition to the demonstrated benefits in growth.  The effects on weight gain, though significant, might only be one part of the benefit of cycled stimulation mimicking intrauterine life for the preterm infant.  Potentially, cycled light may also have a major impact on retinal development and other functions.

Fima Lifshitz, MD