Back when I was a student midwife and as a newly qualified midwife, I intuitively knew that cutting the baby’s cord immediately after the birth was the incorrect thing to do, much to the dismay of my colleagues who would look at me with disgust. Now it has been fully researched and the benefits for the baby are huge.
While the baby is still attached to his/her mother the cord pulsates and during this time baby can receive 80-100 mls of blood helping to reduce the risk of iron deficient anaemia by increasing iron stores..
Evidence suggests that waiting at least 5 or more minutes before cutting the cord, baby continues to receive oxygen through the umbilical cord leading to a reduction in breathing difficulties and less need for oxygen.
Baby can receive more stem cells which having healing qualities, reduce the risk of infections in pre-term babies.
https://www.stuff.co.nz/life-style/parenting/pregnancy/birth/69436870/delay-clamping-babies-umbilical-cords-for-better-health-and-development