One life for another?

There it was, hardly there at all
Not much bigger than a tiny ball
And next to me, there she lay
Her relatives would count each day.
While, inside, a new life it grows,
Another is there, who’s life, it goes.
The illness that put me in here
Tests the foetus’ will to stay in there.
And inside her, there grows another,
Of which her life, it tries to smother.
A malignancy within her brain
While there, in uterine, grows the wain.