Most VLBW infants cannot be fed at the breast upon birth, and expressed breast milk by gastric tube is thus recommended. Sucking skills mature at around 34 weeks when nipple-feeding is introduced. In the absence of evidence-based data to decide the best timing to introduce breastfeeding, many clinicians use empiric criteria, such as the infant's weight, gestational age, and the ability of infants to bottle feed as proxies of readiness to breastfeed. Despite some evidence of physiological benefits of preterm infants feeding at the breast, many neonatologists consider direct breastfeeding to be too fatiguing for preterm infants. It is not known, however, whether preterm infants who are breastfed expend more energy than bottle-fed infants