The fact that the Torah explicitly alludes to the first explanation indicates that it puts priority on the happiness of the couple and on strengthening the relationship between them, even placing this above spiritual and medical explanations. This is so until seven days are past. It is only then that they are counted among the living. The reason based on the newborn's health is supported by medical research done in our generation. These factors rapidly break down, in two or three days, making it necessary for clotting factors to be produced independently, a process that takes place in the liver.
Later exegesis has a tendency to prefer spiritual explanations.
R. Solomon Ephraim of Luncz's Bible commentary, Kli Yakar , focuses on the uncleanness of the newborn. He explains that the woman's menstrual uncleanness is due to the sin in the Garden of Eden. Were it not for this sin, man would be like an angel of G-d, more elevated than the seven planetary systems, but due to his sin he fell from this lofty spiritual state. Everything natural is related to the number seven, and everything spiritual is above nature and therefore related to the number eight. Since the mother is unclean for seven days, this uncleanness also affects the newborn.