Eight studies were included. Three were RCTs and five were studies that used historical controls. The total number of participants appeared to be 1,007 (200 in the RCTs and 807 in the non-randomised studies).
The RCTs had a Jadad quality score of 1 or 2 out of a possible 3. The adequacy of allocation concealment was not reported.
A meta-analysis showed that admission temperature was statistically significantly higher among wrapped infants in 3 RCTs (200 participants); the WMD was 0.63 degrees C (95% CI: 0.38, 0.87, p<0.00001). There was no statistically significant heterogeneity between the studies. A meta-analysis of 5 non-randomised studies (807 participants) showed a larger difference (WMD 0.96, 95% CI: 0.66, 1.27, p<0.00001) with significant heterogeneity between the studies. A regression analysis using data from the RCTs and 2 non-randomised studies showed statistically significant associations between higher admission temperatures and wrapped infants, older infants, warmer mothers and warmer delivery rooms. A significant negative interaction between treatment and gestational age suggested that wrapping was less effective in older infants.
Mortality: a meta-analysis showed no significant difference in mortality in the 3 RCTs or 4 non-randomised studies that reported mortality. Heterogeneity was not statistically significant.
Incidence of hypothermia: a meta-analysis of 3 RCTs showed a statistically significant lower risk of hypothermia in wrapped infants (RR 0.51, 95% CI: 0.37, 0.71), which gave a number-needed-to-treat of 2.9 (95% CI: 2.3, 4.9). Heterogeneity was not reported. The non-randomised studies were highly heterogeneous and, overall, showed no significant difference.
Respiratory problems: the results of the included studies were not reported in full. One study that compared 11 wrapped infants to historical controls reported that the highest FiO2 was significantly lower amongst wrapped infants.
Neurological problems: in one RCT the occurrence of major brain injury was similar amongst wrapped and non-wrapped infants.
Length of stay: in one RCT the length of hospital stay was not significantly different between wrapped and non-wrapped infants.
Adverse events: a meta-analysis showed no significant difference in the risk difference for the incidence of hyperthermia in 3 RCTs or in 2 studies with historical controls. In one RCT none of the participants experienced infection, skin maceration or interference with resuscitation.