The last donation occurred in December 2009, and the last childbirth in December 2012. There were 4361 total person-years of follow-up . Significantly less than 2 percent of pregnancies had been twins. Characteristics of the Study Participants In both study groups, the median age was 29 years , and 29 percent of the women had at least one being pregnant before cohort entry . Needlessly to say, donors had more physician visits in the entire year before cohort access than nondonors because such appointments are a necessary part of donor evaluation. Most donors had been first-degree relatives of the recipient, followed by distant relatives or genetically unrelated donors and spouses .In organisms that grow throughout existence, such as fish, the full total number of cells in a variety of tissues increases continuously, indicating that the amount of fresh cells produced is higher than the number of cells lost. By contrast, the increased loss of normal cells mass and/or architecture to severe damage or disease in humans requires a more intense and qualitatively different regenerative response that restores the tissue to its original condition. This response is named injury-induced regeneration. A major issue for cell transplant therapies is the way to obtain the cells to be utilized. Three sources of cells can be tapped for transplant: differentiated tissues, adult stem cells and derivatives of embryonic stem cells .