Citations are important for a journal to get impact factor. Impact factor is a measure reflecting the average number of citations to recent articles published in the journal. The impact of the journal is influenced by impact factor, the journals with high impact factor are considered more important than those with lower ones. Impact factor plays a major role for the particular journal. Journal with higher impact factor is considered to be more important than other ones. Impact factor can be calculated as average number of citation divided by recent cited articles published in 2 years. Cord blood collection happens after the umbilical cord has been cut and is extracted from the fetal end of the cord, diverting up to 75 +/- 23 mL from the neonate. It is usually done within ten minutes of giving birth. Additional stem cells may be collected from the placenta. After the health care provider draws the cord blood from the placental end of the umbilical cord, the placenta is couriered to the stem cell laboratory, where it is processed for additional stem cells. An adequate cord blood collection requires at least 75mL in order to ensure that there will be enough cells to be used for a transplantation. Before the cord blood is stored for later use, it undergoes viral testing, including tests for HIV and Hepatitis B and C, and tissue typing to determine Human Leukocyte Antigen type. It will also be examined for nucleated cell count, cell viability, blood group antigen ABO & Rh blood group system, molecule cluster (CD34), and bacterial and fungal growth. After the collection, the cord blood unit is shipped to the lab and processed, and then cryopreserved. There are many ways to process a cord blood unit, and there are differing opinions on what the best way is. Some processing methods separate out the red blood cells and remove them, while others keep the red blood cells. However the unit is processed, a cryopreservant is added to the cord blood to allow the cells to survive the cryogenic process. After the unit is slowly cooled to −90 °C, it can then be added to a liquid nitrogen tank which will keep the cord blood unit frozen at −196 °C. The slow freezing process is important to keep the cells alive during the freezing process. There is no consensus yet on optimal procedures for these cord blood cells, although many cryopreservation strategies suggest using dimethyl sulfoxide (DMSO), slow or controlled rate cooling, and rapid thawing. As of 2007, contracts of the largest cord blood banks do not explicitly state that the cord blood belongs to the donors and child with all the rights and privileges one would reasonably expect from ownership. The ambiguity leaves open future uses not approved by the donors and child. At the majority of private cord blood banking facilities, the mother owns all rights to the cord blood that was banked, until the minor in which the cord blood was taken turns eighteen. At that time the minor has all rights to his or her own banked cord blood.