I feel bitter toward my mother for claiming that losing an infant child is worse/more painful than losing an older child
What makes you feel bitter about this conversation with your mom?
In the past I have claimed to my patients that losing a child is almost as hard as living without love.
People view loss differently, but it's understandable that you're frustrated towards your mother as she should be more mindful of the experiences of others. It's good that you support your patients and perhaps you should speak to your mother so she better understands why you think her views are flawed.
I will tell my mom that I'm pregnant now with our second child, 2nd trimester so there is a fair chance baby/ babies will not make it.
Talking to your mom about your feelings, will help both of you to understand how grief affects the both of you. It's important to remember that your mom was sharing her opinion and you should not take it as a person attack.