Kangaroo Care (Patri)
In the early 1980's in Bogota, Columbia, the mortality rate for premature infants was 70%. They had little hospital equipment and unreliable power. Then two local neonatologists began having the infants spend considerable time resting on their mother's chest, skin-to-skin. The mortality rate dropped to 30%, due to a combination of greater infant health and less maternal abandonment due to lack of bonding.

Since then, dozens of studies have demonstrated the measurable, objective benefits of kangaroo care on many of the important measures of infant health: pulse, respiratory rate, oxygen saturation, sleep time, growth rate, time spent in hospital, breastfeeding, breastmilk production, and body temperature. And it clearly has a great positive impact on the less measurable but still important area of bonding.

Basically, the NICU is a scary, weird place. This results in the baby being fussier, overstimulated, and missing out on deep sleep. All of these things use up precious calories and oxygen which could be spent instead on growth and development. When placed in kangaroo care, babies relax and fall into a deep restful sleep which is extremely good for them.

I've just read this book by some of the researchers who have been pioneering KC in the US since the 90's. If you search PubMed you can find lots of studies. This site is devoted solely to kangaroo care, and this is a good intro to the research.

Nor is kangaroo care just for premies. The author suggests that doing it at home until about 52 weeks postconception (so basically through the "fourth trimester"), when sleeping patterns are regularized.