This is one of the classic arguments in favor of abortion, but it really misses the mark for a number of reasons (as you concede at the end of your comment).

The relationship of a mother to a child is not at all equivalent to a person with leukemia. A child isn't a random disease that pops up, it's a new life that was created by the mother via having sex or IVF.

Additionally, an unborn baby can be removed for medical necessity to save the life of the mother without forcibly terminating it -- e.g. through a C-section or by early labor induction. There is no medically necessary reason when saving the mother to terminate the life instead of removing the unborn baby and trying to keep it alive as well. Etc. etc. etc.