I tend to think if any NICU ever had that "rule" (no convertible seats), it was likely an older rule and it was because until the Cocorro (not that long ago), there weren't *any* convertible seats that were rated down to 4 pounds or less. Generally, the car seat challenge is given to preemies, although there certainly are medically fragile babies that are full term and/or full size who need to have it before discharge. To my knowledge, no NICU has a test bench to "install" a car seat on--it's just propped at the correct angle and baby is strapped in while hooked up to the apnea/brady monitors and/or O2 sat monitor. Obviously, any parent can fight the hospital to take their baby home if they do have a proper seat for the child and the child is medically stable enough to go home, but most parents either don't know that or aren't up to the task right then.