There are a few studies investigating factors which contribute to increased human milk use post discharge. Callen and Pinelli found that successful breast feeding in preterm infants (mean gestation 28 weeks) was more likely in mothers who pumped early and continued diligently. In addition to early pumping and lactation support, kangaroo care, and having the experience of breast feeding while still in the NICU have been associated with longer use of human milk and successful breast feeding after discharge. Pineda (2011) looked at the effects of breast-feeding while in the NICU and whether the first oral sucking feeding was at the breast in preterm infants. Mean gestational age when the infant was put to breast was 33.1 weeks + 1.59 weeks. Though challenging for mothers, the ability to continue to maintain breast-feeding during the NICU stay and until discharge as well as having the first feed be at the breast increased overall duration of breast-feeding duration after discharge. Direct breast-feeding also increases oxytocin levels in the mother, which leads to psychological benefits such as improved maternal response and improved attachment behaviors. These factors may indirectly lead to improved use of breast milk.