Abstract: Six studies met the inclusion criteria; however, only five studies provided data for analysis. Four of the six included studies were small and had significant limitations in design. As each study reported outcomes differently, data for most outcomes were effectively contributed by a single study. Study authors reported no differences between co-bedded twins and twins receiving separate care in terms of rate of weight gain (MD 0.20 grams/kg/d, 95% CI -1.60 to 2.00; one study; 18 pairs of twins; evidence of low quality); apnea, bradycardia, and desaturation (A/B/D) episodes (RR 0.85, 95% CI 0.18 to 4.05; one study; 62 pairs of twins; evidence of low quality); episodes in co-regulated states (MD 0.96, 95% CI -3.44 to 5.36; one study; three pairs of twins; evidence of very low quality); suspected or proven infection (RR 0.84, 95% CI 0.30 to 2.31; three studies; 65 pairs of twins; evidence of very low quality); length of hospital stay (MD -4.90 days, 95% CI -35.23 to 25.43; one study; three pairs of twins; evidence of very low quality); and parental satisfaction measured on a scale of 0 to 55 (MD -0.38, 95% CI -4.49 to 3.73; one study; nine pairs of twins; evidence of moderate quality). Although co-bedded twins appeared to have lower pain scores 30 seconds after heel lance on a scale of 0 to 21 (MD -0.96, 95% CI -1.68 to -0.23; two studies; 117 pairs of twins; I2 = 75%; evidence of low quality), they had higher pain scores 90 seconds after the procedure (MD 1.00, 95% CI 0.14 to 1.86; one study; 62 pairs of twins). Substantial heterogeneity in the outcome of infant pain response after heel prick at 30 seconds post procedure and conflicting results at 30 and 90 seconds post procedure precluded clear conclusions. Evidence on the benefits and harms of co-bedding for stable preterm twins was insufficient to permit recommendations for practice. Future studies must be adequately powered to detect clinically important differences in growth and neurodevelopment. Researchers should assess harms such as infection, along with medication errors and caregiver satisfaction.

Plain-language summary: This review found six mostly small studies with some limitations in their methods. All six studies were conducted in the neonatal nursery of a major tertiary hospital. In all studies, researchers enrolled preterm infants of average postmenstrual age of 29 weeks (nearly two and a half months preterm). Some studies enrolled twins only; others enrolled twins and triplets and quadruplets and chose to co-bed two of the higher-order multiples considered most stable at the time of enrollment. Overall, researchers reported no differences between the co-bedded group and the group receiving care separately in terms of weight gain, episodes of major disturbances in their breathing, heart rate or oxygenation level (apnea, bradycardia, or desaturation episodes), length of hospital stay, and occurrence of infection. Conflicting results were noted in the two included studies that assessed infants' pain response after heel prick. Overall quality of evidence was low because of limitations in study methods, small sample sizes giving rise to imprecise results, and inconsistency in study results. We can make no recommendations for or against co-bedding for stable preterm twins in the neonatal nursery on the basis of evidence gathered in this review. Further research on this topic is needed.