At the beginning Parshas Tazria we are told that a woman who gives birth will be tamei (spiritually impure – for none of a better word). Why is this? One answer is as follows: When something kodosh (holy) leaves the world, there becomes a void and a vacuum that is filled with tumah (spiritually impure)- this is perhaps a reason why one says Kaddish for a Jew that departs this world -ie. to fill the void from their passing with the kedusha of Kaddish…
In the same respect a woman who gives birth attains a similar level to HaShem in the sense that ‘she’ has ‘created’ a new life. Therefore, when the birth takes place, the mother is no longer the ‘creator’ (present tense) and so with the absence of that kedusha, there must be impurity.