Using a multisite randomized controlled trial design , stable preterm twins ( 67 sets , N = 134 infants ) between 28 and 36 completed weeks ' gestational age , stratified by gestational age ( and > 32 weeks ) and site , were randomly assigned to a co-bedding group , cared for continuously in the same incubator or crib or a standard care group , cared for in a separate incubator or crib , and underwent a medically indicated heel lance after at least 24 hours and no greater than 10 days of group allocation .