The Watchtower stance on sterilisation has been inconsistent over time. Originally forbidden, it is now simply discouraged for reasons of birth control, and acceptable if a life is at stake.
When deriving rules on sterilisation, the Watchtower refers to the Mosaic law, though it is a vague connection since the Mosaic Law does not forbid voluntary sterilisation in regards to birth control. The Watchtower also admits that neither Jesus or Paul discussed sterilisation at all.
Why is the Watchtower creating rules regarding "reproduction"? The Mosaic Law does not apply to a Christian, and the Watchtower cherry picks which Mosaic laws it wishes to continue to apply? God's command to "fill the earth" is no longer a relevant consideration, as the earth has been filled. It is illogical, unchristian and harmful to be referring to a 3000 year old Law that is now redundant. There is similarity in this matter between how the Watchtower Governing Body and the Catholic Pope go beyond the Scriptures.
An experience from an elder highlights why the Watchtower show not be invasive in this regard.
"A publisher who was studying with her domestic servant approached me on the subject. The domestic was battling to survive, had an unemployed husband, and six children. The domestic had mentioned that she was considering sterilization (in local culture the men refuse to use contraceptives). The publisher had discussed this with one elder, who trotted forth all the society's viewpoints. She then asked me as a second opinion. My simple question was: "Why don't we all mind our own business, and let this woman discuss it with her doctor, and make her own decision? Are you, or the society, going to support her if she falls pregnant again?" Naturally, this stirred up a hornet's nest."
Watchtower 1999 Jun 15 pp.27-28
"A central point is that reproductive powers are a gift from our Creator. His original purpose included procreation by perfect humans, who would “fill the earth and subdue it.” (Genesis 1:28) After the Flood cut earth’s population to eight, God repeated those basic instructions. (Genesis 9:1) God did not repeat that command to the nation of Israel, but Israelites viewed having offspring as something very desirable.—1 Samuel 1:1-11; Psalm 128:3. God’s Law to Israel contained indications of his regard for human procreation. For example, if a married man died before producing a son to carry on his lineage, his brother was to father a son by brother-in-law marriage. (Deuteronomy 25:5) More to the point was the law about a wife who tried to help her husband in a fight. If she grasped the privates of her husband’s opponent, her hand was to be amputated; significantly, God did not require eye-for-eye damage to her or her husband’s reproductive organs. (Deuteronomy 25:11, 12) This law would clearly engender respect for reproductive organs; these were not to be destroyed needlessly.
We know that Christians are not under Israel’s Law, so the regulation at Deuteronomy 25:11, 12 is not binding on them. Jesus neither ordered nor implied that his disciples must marry and have as many children as possible, which many couples have considered when deciding on whether to use some method of birth control. (Matthew 19:10-12) The apostle Paul did encourage passionate ‘younger widows to marry and bear children.’ (1 Timothy 5:11-14) He did not bring up the permanent sterilization of Christians—their voluntarily sacrificing their reproductive potential to bear children. Christians do well to weigh such indications that God esteems their reproductive ability. Each couple must determine if and when they will employ appropriate methods of family planning. Granted, their decision would be particularly telling if there were confirmed medical assurances that mother or child faced grave medical risks, even a probability of death, with a future pregnancy. Some in that situation have reluctantly submitted to a sterilization procedure as described earlier to make sure that no pregnancy would threaten the life of the mother (who may already have other children) or that of a child who might later be born with a life-threatening health problem.
But Christians who are not facing such an unusual and distinct risk would certainly want to use ‘soundness of mind’ and shape their thinking and deeds by God’s esteem for reproductive potential. (1 Timothy 3:2; Titus 1:8; 2:2, 5-8) This would reflect mature sensitivity to Scriptural indications. Yet, what if it became publicly known that a Christian blithely disregarded God’s evaluations? Would not others doubt whether he (or, she) was a good example, having a reputation of making decisions in harmony with the Bible? Such a disturbing blemish on one’s reputation could, of course, affect a minister’s being qualified for special privileges of service, though that might not be so if one had in ignorance had this procedure performed."
Awake 1996 10/8 p.14 Who Should Decide Family Size?
"Are all methods for limiting family size valid? No. Since life is sacred, God’s Law to Israel decreed that one who caused an abortion be treated as a murderer. (Exodus 20:13; 21:22, 23) In the case of sterilization, such as by a vasectomy, the decision is one of personal conscience, since this is not directly mentioned in the Bible . “Each one will carry his own load.”"
it-2 p.1089 Testicles
In the case of the Christian congregation, persons who have been castrated are not barred from entry, for the Law has been set aside on the basis of Christ’s sacrifice. (Col 2:13, 14) Nevertheless, the laws above quoted illustrate God’s regard for the reproductive organs and strongly indicate that an operation that would destroy a person’s procreative powers simply because he had no appreciation for that gift from God would be wrong.
Watchtower 1975 3/1 pp.158-160 Questions from Readers
"Would a husband’s approving of sterilization (either for himself or for his wife) disqualify him from positions of congregational responsibility? [p.158]
In view of these Scriptural points, it should be evident that the bearing of children has divine approval. Hence, it would be wrong for one to submit to sterilization or approve of sterilization of one’s wife simply because one has no appreciation for God’s gift of the procreative powers. What, however, of the situation where one’s wife has given birth to children but has had to do so through surgical operations, such as cesarean section? She may have had as many as three such operations and her physician may warn her that a further pregnancy could place her in serious danger of experiencing womb rupture, generally fatal to both the mother and the fetus. Would sterilization in such a case necessarily show disrespect for the divine gift of procreation?
It seems evident that the couple have not manifested a light attitude toward their procreative powers, having already brought forth children. They may view sterilization as a procedure advisable to protect the life of the mother of the children already produced. They may view it as a ‘last resort.’ Thus in making their decision they may feel that it is a question of balancing respect for God’s provision of the procreative powers with respect for the gift of life itself, in this case the life of the endangered mother. For this reason, and for additional reasons, it appears that such a decision is one that rests on the individual consciences of those involved. [pp.158-159]
The qualifying for congregational responsibility on the part of a man who approves of sterilization due to his wife’s endangered state, then, is one that must be weighed in the light of Bible principles by the local body of elders. Does his life pattern as a whole show that he has deep respect for God’s Word or does he make light of its counsel? Does he show himself to be conscientious and serious in his decisions? If his motive in approving of sterilization were due to lack of respect for God’s standards, this disrespectful attitude would likely be manifest in other ways as well. On the other hand, if he measures up to the Scriptural requirements for those having congregational responsibility as set forth in 1 Timothy 3, Titus 1 and other texts, then the fact that his conscience allows for surgical sterilization as a life-protecting measure need not of itself disqualify him. Of course, the attitude of the congregation must be considered. If the matter became an issue of such proportion that it distracted measurably it could seriously limit his ability to serve with effectiveness. Weighing these factors, the elders should then make their decision." [p.160]
Watchtower 1964 3/1 p.159 Questions From Readers
"Sterilization, whether temporary or permanent, for the specific purpose of birth control would Scripturally be wrong. "
Watchtower 1961 12/1 p.735
"It is true that the Mosaic law containing the above provisions was done away with in Christ, but God has not changed his attitude on sterilization. The sense, the force, the basic, inherent idea and purport of the above laws remain in effect with respect to Christians, who are under a law even higher than that given through Moses. A dedicated Christian is under the law of loving Jehovah God with the whole heart, mind, soul and strength. The force and effect of sterilization is against this, as sterilization harmfully affects the asexualized person physically and mentally. A Christian is not a habitual criminal or an imbecile that needs to be sterilized.
If a doctor claims that for a wife to have another child it would mean the death of her, then what? Then there is another way to prevent her conception, which conception might bring her life in jeopardy, than by violating the law of God, the whole tenor of which is contrary to deliberate asexualizing of a man or woman. If parents are living in poverty and could not afford to have another child, then there is another way to take care of this economic situation than by ruining those organs with which the perfect man and woman were endowed and which enter so strongly into the noble purposes of married life. There is the need for exercising the spirit of the Lord God, one of the fruits of which is self-control."