Grajeda R, Perez-Escamilla R, Dewey KG Delayed clamping of the umbilical cord improves hematologic status of Guatemalan infants at 2 months of age Am J Clin Nutr 1997 (Feb); 65 (2): 425-431
Premature babies who experienced delayed cord clamping--the delay was only 30 seconds--showed a reduced need for transfusion, less severe breathing problems, better oxygen levels, and indications of probable improved long-term outcomes compared with those whose cords were clamped immediately.
Kinmond S, Aitchison TC, Holland BM Umbilical cord clamping and preterm infants: a randomised trial Brit Med Jou 1993 (Jan 16); 306 (6871): 172-175
Some studies have shown an increased risk of polycythemia (more red blood cells in the blood) and jaundice when the cord is clamped later. Polycythemia may be beneficial in that more red cells mean more oxygen being delivered to the tissues. The risk that polycythemia will cause the blood to become too thick (hyperviscosity syndrome), which is often used as an argument against delayed cord clamping, seems to be negligible in healthy babies.
Morley, G Cord closure: Can hasty clamping injure the newborn? OBG Mgmnt 1998 (Jul): 29-36
Some evidence shows that the practice of clamping the cord, which is not practiced by indigenous cultures, contributes both to postpartum hemorrhage and retained placenta by trapping extra blood (about 100 mL) within the placenta. This increases placental bulk, which the uterus cannot contract efficiently against and which is more difficult to expel.
Walsh, S Maternal effects of early and late clamping of the umbilical cord Lancet 1968 (May 11); 1 (7550): 996-997
Clamping the cord, especially at an early stage, may also cause the extra blood trapped within the placenta to be forced back through the placenta into the mother's blood supply during the third stage contractions. This feto-maternal transfusion increases the chance of future blood group incompatibility problems, which occur when the current baby's blood enters the mother's bloodstream and causes an immune reaction that can be reactivated in a subsequent pregnancy, destroying the baby's blood cells and causing anemia or even death.
Doolittle, J. & Moritz Obstet Gynecol 1966; 27:529 and Lapido, O. (1971, March 18). Management of the third state of labour with particular reference to reduction of feto-maternal transfusion. BMJ 1971 (Mar 18); 721-723
The above are excerpts from Sarah Buckley's "A Natural Approach to the Third Stage of Labour," Midwifery Today Issue 59