All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
If tying a woman`s tubes (Tubal ligation) is intended as a treatment for a present or an expected disease, then there is no sin in it. However, if it is intended to control birth for fear of poverty, then it isn`t permissible because Allah the Almighty says (What means): " Kill not your children for fear of want: We shall provide sustenance for them as well as for you. Verily the killing of them is a great sin." {Al-Isra`, 31}.
It is worth indicating that a woman should be treated by a woman, but if this wasn`t possible then there is no sin in being treated by a male doctor. However, this is provided that decency is observed and gaze is lowered; particularly with regards to the genitals. And Allah the Almighty knows best.