On this matter, each Christian couple can evaluate the relevant facts and Bible principles. Then they should make a decision in such a way as to maintain a good conscience before God.

Back when there were just two humans (and after the Flood, eight), Jehovah commanded: “Be fruitful and become many.” (Gen. 1:28; 9:1) The Bible does not say that such a command applies to Christians. Hence, it is up to each couple to determine whether to use some form of birth control to limit the size of the family or to determine when to have children. What factors merit their consideration?

Christians ought to weigh any birth control method in the light of Bible principles. Thus, Christians reject abortion as a means of birth control. Voluntary abortion conflicts with what the Bible says about respect for life. Christians would not choose to terminate a life that in time would normally result in the birth of another human being. (Ex. 20:13; 21:22, 23; Ps. 139:16; Jer. 1:5) What about the use of an IUD?

This matter was addressed in The Watchtower of May 15, 1979, pages 30-31. Most IUDs that were then widely available were inert plastic objects inserted in the uterus (womb) to prevent pregnancies. The article noted that it was not fully known how such IUDs functioned. Many specialists said that inert IUDs caused a reaction in the uterus that interfered with sperm reaching and fertilizing a woman’s eggs. If fertilization did not occur, a new life did not begin.

 Yet, some evidence suggested that an egg occasionally could get fertilized. The newly fertilized egg might grow in a Fallopian tube (an ectopic pregnancy) or might travel into the womb. In the latter case, the presence of the IUD could interfere with the fertilized egg’s implanting in the lining of the womb and progressing as a normal pregnancy would. Ending the developing life would be like an abortion. That article concluded: “The sincere Christian concerned about the propriety of using an IUD should seriously weigh such information in the light of a Bible-based respect for the sanctity of life.”​—Ps. 36:9.

Have there been significant scientific or medical developments since that article was published in 1979?

Two types of IUDs have come to the fore. One type of IUD that incorporates copper became widely available in the United States by 1988. In addition, IUDs that release a hormone came on the market in 2001. What is understood about how these two types function?

Copper: As mentioned, IUDs seem to make it difficult for sperm to survive passing through the uterus to reach an egg. In addition to that, with copper-releasing IUDs, the copper appears to be toxic to sperm, acting as a spermicide. * Moreover, copper-containing IUDs are said to alter the lining of the uterus.

Hormone: There are different types of IUDs that contain a hormone similar to what is often found in birth control pills. These IUDs release the hormone in the uterus. It appears that such IUDs suppress ovulation in some women. Of course, if no egg is released, fertilization cannot occur. Beyond that mechanism, it is held that the hormone in these IUDs thins the lining of the uterus. * It also thickens the mucus at the cervix, thus creating a barrier to sperm moving from the vagina into the uterus. These effects are in addition to that produced by inert IUDs.

As noted, both types of IUDs appear to alter the lining of the uterus. Yet, what if ovulation does occur and an egg is fertilized? It might enter the uterus but fail to implant in the less receptive lining. That would end the pregnancy at an early stage. However, instances of such “failed” implantations are thought to be rare, even as seems to be the case occasionally with oral contraceptive pills.

Hence, no one can say with certainty that IUDs that include copper or a hormone never allow for the fertilization of an egg. However, scientific evidence suggests that because of a number of mechanisms mentioned above, pregnancy rarely occurs with the use of such IUDs.

A Christian couple considering the use of an IUD might discuss with a qualified medical professional the IUD products available locally as well as possible benefits and risks to the wife. The couple should not expect or allow a third party, not even a physician, to determine what they will do. (Rom. 14:12; Gal. 6:4, 5) It is a private decision. They should make their decision as a couple interested in pleasing God and maintaining a clean conscience before him.​—Compare 1 Timothy 1:18, 19; 2 Timothy 1:3.