Sterilisation: a form of mutilation of the human body, is an operation which makes the woman incapable of bearing children or the man incapable of becoming a father.
It is again the teaching of the Church that sterilisation for the purpose of birth control is another form of contraception. Both distort the meaning of the marital act by destroying its fertility.
The marital act (intercourse) has two purposes and meanings: it is love-giving and life-giving… the essence of God! – Page 45