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In general Roman Catholics believe that using infertility treatments is wrong, this stems from four main ideas. Romans believe that life is a gift from god and so we as humans do not have the right to tamper with it. People do not have the right to have a child; it is a privilege from god. Children are not a commodity that should be bought or altered etc they are a gift from god. The soul is implanted into a person at conception so if they are not properly conceived i.e. in a test-tube the soul may not be present. As the soul is present from conception in the eyes of the church the embryo has the status of a human and so any research carried out is wrong. To throw the unused embryos is throwing away human life which is just the same as any other murder which is obviously wrong. Roman Catholics follow natural law, this state that anything that is good must be from something natural. So therefore having a child through complicated medical procedures which are unnatural is wrong.
Most other Christians who are not Roman Catholic do not follow natural law. Non Roman Catholics will normally look to the bible and the teachings of Jesus especially the commandments about love. They might use situation ethics, where you must do what the most loving thing is. They would think that an embryo is life but merely potential life. Because they don't think the embryo is a "proper" person then it is ok to perform research on the embryo. They believe that using treatments like GIFT and IVF are just using Gods" gift of intelligence and it is what he wants. .
The majority of Muslims would do not totally reject all forms of infertility but still allow some.
They believe like Roman Catholics that life is gift from god and as such it shouldn't be tampered with. They believe that all children should be born into married couples otherwise the child is illegitimate. If the child does not know who both of there parents are then it is wrong to have the child.