Speaking of fetus and conformational and functional changes, hemoglobins also go through some significant changes from fetal stages to adulthood. There are different types of hemoglobins expressed in the fetus that gets unexpressed.
Fig 1. This shows the different types of hemoglobin genes expressed during fetal stages and adult life.
Fig 2. Schematic representation of hemoglobin gene regulations.
All in all, sometimes it is important to view the functions and purposes of organs and appendages from an evolutionary developmental perspective, also known as evo-devo.