“INTRAUTERINE CONTRACEPTION: PATIENT AND CLINICIAN CONSIDERATIONS” LEE SHULMAN, MD, HENRY M. HESS, MD, PHD, RAQUEL ARIAS, MD, ANDREW LONDON, MD, MBA, AND SUSAN WYSOCKI, RN (SUPPLEMENT; JULY)
I question the statement, in this supplement to OBG Management, that the mechanism of action of intrauterine contraceptives is spermicidal. This implies that an intrauterine device (IUD) is not an abortifacient. Yet, the 2009 edition of The Physicians’ Desk Reference describes the “possible mechanism(s) by which copper enhances contraception efficacy, [which] include interference with sperm transport or fertilization, and prevention of implantation.”
I am a believer in a woman’s right to choose. However, I believe that the statement that intrauterine contraceptives are spermicidal is, at best, begging the question of accuracy.
Robert S. Ellison, MD
Dr. Shulman responds: Data strongly refute the claim that the IUD is abortifacient
Dr. Ellison is correct about the description of the mechanism of action of intrauterine contraceptives found in the PDR. This description also appears on the package inserts of the two commercially available IUDs, in recognition of the fact that they can prevent pregnancy by prefertilization and postfertilization mechanisms.
Numerous studies have been performed to ascertain the mechanism of action of the IUD. In a review of the literature, Ortiz and colleagues present the prevailing view that the IUD enhances the inflammatory response that helps to phagocytize sperm and interfere with sperm capacitation; they also argue that this is the primary basis for the prevention of pregnancy when an IUD is the method.1
When an IUD is in place, a relatively small number of spermatozoa reach the distal segment of the fallopian tubes—and most of these spermatozoa are incapable of fertilization.2 In one study involving the recovery of eggs, no fertilized eggs were recovered from the fallopian tubes and upper uterus of women who had an IUD in place. In contrast, more than 50% of eggs were fertilized in women who used no contraception.3
It is for these reasons—and the absence of a rise in human chorionic gonadotropin in women who use the IUD2—that intrauterine contraceptives are thought to prevent pregnancy primarily by spermicidal actions.
Perhaps two other issues need to be addressed:
- The fact that the IUD causes an inflammatory response in the uterus that can have an anti-implantation effect does not mean that this is a preeminent mechanism of action
- It is impossible to “prove a negative.” The possibility that the IUD might prevent pregnancy through effects on implantation was the basis for including those statements in the original package inserts. Proving that the IUD doesn’t prevent pregnancy by this mechanism is impossible.
Nonetheless, the available evidence is clear: The IUD prevents pregnancy by preventing conception, not by preventing implantation. Governmental agencies and medical societies have uniformly supported this premise. The publication in a package insert of a biologically plausible mechanism of action—a mechanism that has not been shown to be clinically relevant—says more about the continuing inadequacy of package inserts and the manner in which they are developed than it does about the abortifacient nature of the IUD.
The IUD is an important and vital option for women seeking safe and reliable methods, especially for those seeking a nonhormonal (Copper T380A) or non-oral (Copper T380A and levonorgestrel-releasing intrauterine system) method.