Describe the effectiveness and safety of cycled light (approximately 12 hours of light on and 12 hours of light off) for growth in preterm infants at three and six months' corrected age. By exploring separate questions, we compared the effectiveness of cycled light with that of irregularly dimmed light or near darkness, and we compared cycled light with continuous bright light, for growth in preterm infants at three and six months' corrected age.
Potential benefits and harms of different lighting in neonatal units have not been quantified. The pregnant woman is exposed to variable intensities of light and sound, and generally to lower levels at night. Some of the light and sound reaches the foetus within 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 and no other circadian entraining signals. Infants are exposed to continuous bright light, continuous near darkness or an unstructured combination of the two.
We included a total of nine randomised and quasi-randomised trials, which enrolled 544 infants.
Study funding resources
To our knowledge, no studies included in this review were funded by industry.
No study reported on weight at three or six months. One study reported improved growth at three months of age in infants exposed to cycled light compared with those exposed to continuous bright light. Another study found no difference in weight at four months of age. Length of hospital stay was shortened with cycled light in the nursery compared with near darkness or with continuous bright light. Only a few outcomes reached statistical significance, which is likely to be due to the small number of infants enrolled in these studies, but trends for most outcomes (weight gain, incidence of retinopathy of prematurity, time spent crying) favoured cycled light over near darkness, and cycled light over continuous bright light.
Quality of evidence
The quality of the evidence on outcomes assessed was low because the interventions could not be blinded to caregivers, and few infants were enrolled in these studies.
Trials assessing the effects of CL have enrolled 544 infants. No study reported on our primary outcome of weight at three or six months. Results from one additional study strengthen our findings that CL versus CBL shortens length of stay, as does CL versus ND. The quality of the evidence on both comparisons for this outcome according to GRADE was low. Future research should focus on comparing CL versus ND.
Potential benefits and harms of different lighting in neonatal units have not been quantified.
• To determine effectiveness and safety of cycled light (CL) (approximately 12 hours of light on and 12 hours of light off) for growth in preterm infants at three and six months' corrected age (CA).
• In separate analyses, to compare effects of CL with those of irregularly dimmed light (DL) or near darkness (ND), and effects of CL with those of continuous bright light (CBL), on growth in preterm infants at three and six months' CA.
• To assess, in subgroup analyses, the effectiveness and safety of CL (vs control interventions (DL, ND and CBL)) introduced at different postmenstrual ages (PMAs) - before 32 weeks', at 32 weeks' and from 36 weeks' PMA - and to compare effectiveness and safety of CL for small for gestational age (GA) infants versus appropriately grown infants.
We used the standard search strategy of the Cochrane Neonatal Review Group to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 12), MEDLINE via PubMed (1966 to January 2016), Embase (1980 to January 2016) and the Cumulative Index to Nursing and Allied Health Literature (CINAHL; 1982 to January 2016). We searched clinical trials databases, conference proceedings and reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.
Randomised or quasi-randomised trials of CL versus ND or CBL in preterm and low birth weight infants.
We performed data collection and analyses according to the methods of the Cochrane Neonatal Review Group. We used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to assess the quality of evidence.
We identified one additional study enrolling 38 participants for inclusion in this update, for a total of nine studies reporting on 544 infants. In general, the quality of the studies was low, mainly owing to lack of blinding and small sample sizes.
Six studies enrolling 424 infants compared CL versus ND. No study reported on weight at three or six months. One study (n = 40) found no statistically significant difference in weight at four months between CL and ND groups. In another study (n = 62), the ratio of day-night activity before discharge favoured the CL group (mean difference (MD) 0.18, 95% confidence interval (CI) 0.17 to 0.19), indicating 18% more activity during the day than during the night in the CL group compared with the ND group. Two studies (n = 189) reported on retinopathy of prematurity (stage ≥ 3) and reported no statistically significant differences between CL and ND groups (typical risk ratio (RR) 0.53, 95% CI 0.25 to 1.11, I2 = 0%; typical risk difference (RD) -0.09, 95% CI -0.19 to 0.01, I2 = 0%). Two studies (n = 77) reported length of hospital stay (days) and noted a significant reduction in length of stay between CL and ND groups favouring the CL group (weighted mean difference (WMD) -13 days, 95% CI -23 to -2, I2 = 0%; no heterogeneity). The quality of the evidence according to GRADE was low for this outcome. One study (n = 37) reported less crying at 11 weeks' corrected age (CA) in the CL group compared with the ND group (MD -0.57 hours/24 h, 95% CI -1.09 to -0.05). Tests for heterogeneity were not applicable.
Three studies enrolling 120 infants compared CL versus CBL. Two studies (n = 79) reported significantly shorter length of stay in the CL group compared with the CBL group (WMD -16.5 days, 95% CI -26.2 to -6.8, I2 = 0%; no heterogeneity). The quality of the evidence according to GRADE was low for this outcome. One study (n = 41) reported higher mean weight at three months' CA among infants cared for in the CL nursery (P value < 0.02) and a lower mean number of hours spent awake in 24 hours at three months of age (P value < 0.005). Data could not be entered into RevMan or GRADE. One study (n = 41) reported shorter time on the ventilator in the CL compared with the CBL group (MD -18.2 days, 95% CI -31.40 to -5.0). One study (n = 41) reported a shorter time to first oral feeding in the CL group (MD -6.8 days, 95% CI -13.29 to -0.31). We identified no safety issues.