/women that have never had children really can not truly relate to childbirth and the changes that are forever a consequence.
That's fair. And parenthood is, from what I hear

a unique experience like no other.
However, there are many experiences that one friend may have had, that are also unique and like no other, yet they are friends with people who have not had that experience!
So I will maintain that it is the actual mechanics and logistics of those consequences, not necessarily an emotional thing on the part of the friend who is a mother that her childless friends are simply no longer friend material, that is responsible for those friendships that do suffer when one becomes a parent.
And I agree with the poster who pointed out that the "suffering" of the friendship doesn't always wait for a baby to arrive, but in many, in fact, I will say most - cases can trace its origins to the days when the relationship with the Significant Other becomes "serious."
THAT's when the availability of the newly enamored friend begins to downturn, especially availability of her alone - without the SO, and as was recently discussed in another thread, brunch with two of your closest girlfriends is one thing. Brunch with two of your closest girlfriends and the newly acquired SO of one of them is a whole different event!
You can compare it, I think, to a friend who moves to a distant state or country. It is not that the feelings between you have changed, but the logistics and circumstances of the life of one of you has! And before you know it, the same thing happens to you, and time passes, and one day before you know it you are astonished to realize just how fortunate you are to have friends you have had for more years than either of you would wish to admit to reporters, should they ask, and maybe you only see each other, or even talk on the phone, occasionally, even very very occasionally.
But you do not love each other any less!