Interest in cobedding multiple-gestation infants has grown as focus has increased on the developmental approach to the care of the neonate. Little data, however, exist on the infants' response to cobedding. It is important to evaluate the safety, efficacy, and physiologic impact of this practice. Cobedding was offered to parents of twin infants < 37 weeks gestation, without arterial lines or ventilator requirements, by the health care team according to standard practice in our nursery. After parental informed consent, infants were placed on an event-recording cardiorespiratory monitor for 12 hours before cobedding and for the first 12 hours of cobedding. Recordings were evaluated by an investigator blinded to the bedding status of the infant. Apnea (a pause of respiration > 10 seconds, central apnea), bradycardia (a decline in heart rate to < 80 beats per minute), periodic breathing (a respiratory pattern in which there are > or = 3 pauses in respiration of > or = 3 seconds with < 20 seconds of breathing between pauses), adverse events (changes in medication, changes in oxygen requirements, temperature instability, the need for sepsis evaluation, or death) were evaluated. Other physiologic parameters were obtained through the use of standard bedside monitoring. Eleven sets of preterm infants, n = 22, with a mean gestation of 31.8+/-2.9 weeks and a mean birth weight of 1,698.7+/-552.0 grams were studied. Infants were evaluated at a corrected gestational age of 33.5+/-1.9 weeks and a mean weight of 1,713.2+/-484.0 grams. The number of events of central apnea before cobedding (57) was greater than those recorded during cobedding (18), p<0.05. There was no difference found in any of the other parameters compared. The numbers of events recorded before and during cobedding were compared by Student's t-test and significance was determined by p < 0.05. No adverse events (AE) were noted, and all infants remained cobedded throughout the study. This preliminary study suggests that cobedding of healthy preterm twins showed no increase in adverse events. Of the physiologic parameters studied, only the occurrence of central apnea changed with cobedding. This decrease in central apnea may reflect a change in sleep pattern due to more frequent arousal by the twin. Alternatively, a more regular breathing pattern may reflect a positive physiological response to contact between twins.