The 4th Trimester Project, organized by a team of researchers at the University of North Carolina's Center for Maternal and Infant Health, focuses on information and research about new mothers' experiences. They explain:
The term “4th Trimester” reflects the concept that during the first months of life, newborns continue to function like a fetus in many ways; they require months of intense, ‘womb-like’ nurturing. A 4th Trimester perspective views the mother and infant as a mutually dependent unit, behaviorally and physiologically intertwined via breastfeeding and other interactions such as skin-to-skin contact. These infant demands require a substantial transformation for mothers, who are recovering from the physical sequelae of childbirth and coping with altered sleep patterns.