There are different way it affects the mother and unborn child. there is the physical and mental aspect.
1. As the mother attends classes, the baby is being adjusted in the right position it should adopt in order to come out the right way.
2, The mother exercise herself ,thereby developing muscles in essential areas she needs in order to have the "muscle" to give birth like the thigh and abdominal muscles.
3. The mother learns the necessary information she needs to have a successful delivery and what to do after child birth and at the nursing stage.
I can't list all but these are the key points/reasons