It's so obvious.
And it's so wrong.
It is not in Carrie Bradshaw's character to have a child. Mr. Big and Carrie especially do not mix with children. Mr. Big's elegance and dapper Old New York ways do not work with diapers; there is a reason he was not there for Brady's birth. Carrie's column would then morph into a parenting one, and her fabulosity would not overrule the dullness of the subject.
There are people who believe that Carrie is the eternal single woman--she should not and cannot get married. But it is her with a child that seems even more incongruous with her luxurious, wanderlustful lifestyle.
They should stop messing with "Sex and the City", because it will dilute the product.