I can see you have had plenty of recommendations on pregnancy and childbirth books. So from physical well being let us look at metaphysical well being.
Reading 'Sundarakandam' will generate mental peace and well being for both mother and child. This is something my grandmother told me. I've tried it. I don't know if it works but the process of sitting down quietly and focussing the mind positively helps settle any nerves, anxiety and physical discomfort.
I was asked to avoid reading books like the Mahabaratha. Again dont know if that does generate negativity. But hey ho one cant take a chance with something as crucial as pregnancy!