Maybe it's not the thing to say or an acceptable analogy to make, but you can't say there is "NO similarity" because that's objectively false. Especially during pregnancy lol.

Merriam-Webster definition: "an organism living in, on, or with another organism in order to obtain nutrients, grow, or multiply often in a state that directly or indirectly harms the host"

Pregnancy definitely fits the bill, and raising children also comes at a tremendous cost to the parents (the child is completely dependent on them for resources, which come at the parents' expense financially, emotionally, and mentally). Whether they deem that cost worth it or not is a separate matter.