That causes less blood to flow inside the umbilical vein and inside the doctor's venosis. And this eventually becomes non functional and ceases to function and ceases to exist. Now, another important change that takes place is the thickening of the left ventricle compared to the right ventricle. So before that fetus is actually born, the size of the wall of the right ventricle is greater than the size of the wall of the left ventricle. And that's because the right ventricle has to pump blood against a higher pressure to the lungs. Now, what happens after birth is we have a reversal of pressure, and so the pressure in the lungs drops.