Ahmad Muhammad, from the Department of Infectious Diseases, Primary Health Care Office, Saudi Arabia, and the author of Al-Mausu’atu Tibbiyyatul Fiqhiyyah, says:
The way IUD works is different from that of contraceptive pills. The contraceptive pills prevent ovulation, but IUD works mechanically-that is- it prevents egg from nesting in the uterine wall. The egg may have been fertilized by the sperm, but this does not mean that the IUD causes the abortion of the fetus. Rather, the IUD only prevents the egg from nesting and that leads to its death. Thus, it falls outside the uterus before even becoming a fetus.
Hence, there is no Sharia objection in using IUD to prevent pregnancy because it does not work as abortion; knowing fully well that some jurists have permitted abortion of fetus before soul is breathed into it, though subject to different scholarly opinions.
Some scholars prohibited abortion after 40 days from the beginning of pregnancy, and some of them prohibited it after four months or 120 days. However, the IUD causes the egg to fall long before it becomes a fetus and that is permissible.