Changes in the newborn at birth

As soon as the baby emerges, the healthcare provider clamps and cuts the cord and takes stimulatory measures to help the baby take his first breath (this is why the baby is sometimes "spanked" to encourage crying and therefore breathing).

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There are many motivators for the baby to take the first breath:

temperature change
light stimulation
physical stimulation
lack of oxygen supply (since the cord is cut)
negative pressure in the chest cavity resulting from the recoil of the chest after exiting the vaginal canal

Once the cord is cut and the baby takes his first breath, a number of changes occur in the newborn's vascular system. The increased oxygen in the lungs causes a decrease in blood flow resistance to the lungs. There is also an increase in the blood flow resistance of the body's vessels.

The lack of umbilical blood flow, decreased pulmonary vascular resistance, and increased systemic vascular resistance cause a closure of the foramen ovale. All the other vascular (blood supply) peculiarities of the fetus begin to constrict and eventually turn into supporting ligaments with no vascular responsibilities.

Now the newborn's blood flow is internalized, gas exchange occurs in the lungs, waste products are removed through urination and defecation, and nutrition is obtained through the digestive system. The newborn undergoes dramatic changes in the processes that sustain life, and these new methods take some time to fully adapt and become permanent.