The Poisoned Source is a book by Tissaia de Vries which is said to respond to the question of whether individuals are born mages or not, and whether or not mages should reproduce.
Excerpt
These morons and cretins can also have offspring, can pass on abilities and this degenerate further. Is anyone in a position to foresee or describe how the last link in such a chain will look?
Most of us wizards lose the ability to procreate due to somatic changes and dysfunction of the pituitary gland. Some wizards — usually women — attune to magic while still maintaining efficiency of the gonads. They can conceive and give birth — and have the audacity to consider this happiness and a blessing. But I repeat: no one is born a wizard. And no one should be born one! Conscious of the gravity of what I write, I answer the question posed at the Congress in Cidaris. I ask most emphatically: each one of us must decide what she wants to be — a wizard or a mother.
I demand all apprentices be sterilised. Without exception.