Delaying umbilical cord improves some outcomes in preterm infants, according to an opinion issued by The American College of Obstetricians and Gynecologists. Clamping the cord at least 30-60 seconds after birth increases the baby's blood volume, reducing the need for blood transfusion and the chance of iron deficiency.
Despite the benefits, the ideal time for cord clamping has not been established. Women who have chosen a physiological third stage with a term baby in a midwife-attended birth will usually find that the midwife does not clamp the cord until after the placenta has been born. However, scientific studies seem to want to pin down a time frame around cord clamping. I'd suggest that the results will not be reliable when we impose an arbitrary time frame around cord clamping. We find that babies who are needing extra time to adjust to newborn life tend to have a cord that pulsates for longer, while babies who adjust rapidly have cord that tend to stop pulsating sooner. I find that cord pulsations cease shortly before the placenta is born, so there seems to be an intelligent physiological process at play when we leave well alone with the cord and await the natural delivery of the placenta.