The IUD: An Upstream Battle to Clear Its Name
Abstract & Commentary
By Alison Edelman, MD, MPH, Associate Professor, Assistant Director of the Family Planning Fellowship, Department of Obstetrics & Gynecology, Oregon Health & Science University, Portland, is Associate Editor for OB/GYN Clinical Alert.
Dr. Edelman has no financial relationship to this field of study.
Synopsis: The levonorgestrel-releasing intrauterine device prevents sperm penetration at mid-cycle, more evidence to support a mechanism of action.
Source: Lewis RA, et al. Effects of the levonorgestrel-releasing intrauterine system on cervical mucus quality and sperm penetrability. Contraception 2010;82:491-496.
Lewis and colleagues performed an investigator-blinded study of sperm penetrability and quality of mid-cycle cervical mucus between levonorgestrel-releasing intrauterine device (LNG-IUD) users (n = 14) and hormone-free controls (n = 16). Cervical mucus was graded using a standardized analysis from the World Health Organization (WHO). Sperm penetrability was tested using two different testing methods (WHO simplified slide test and Kremer sperm cervical mucus penetration test), which basically monitored for sperm penetration (yes/no) over time and, if penetration, to what depth. Only 14% of LNG-IUD users had favorable cervical mucus at mid-cycle compared to 69% of the control group. None of the LNG-IUD users demonstrated sperm penetration by either test at any time point vs the control group that had 64% (WHO test), 85% at 2 hours (Kremer test), and 79% at 6 hours (Kremer test).
Although studies continue to demonstrate the contrary,1 the IUD continues to be plagued by the belief that it is an abortifacient. However, most of these studies have focused on older IUD models (i.e., copper IUD) and not the LNG-IUD. Several mechanisms of action are thought to play a role in the contraceptive effect of the LNG-IUD including endometrial suppression and cervical mucus viscosity similar to other progestin-only contraceptives.2,3 Lewis et al set out to prove the LNG-IUD effects on cervical mucus. This elegant study found that LNG-IUD users had no sperm penetration at the most fertile time point in their cycles (the authors included a picture of this phenomenon that is well worth a look).
So what happens if sperm manages to navigate the impenetrable mucus of a LNG-IUD user? Obviously, this would have to occur around mid-cycle for it to be a potential concern. There is a consistent body of evidence across different IUD types (inert, copper, and LNG-releasing) that demonstrate a non-abortifacient effect. These experiments have shown that the sterile inflammatory environment created by an IUD inactivates and destroys sperm.4 In fact, no sperm were found in the fallopian tubes of IUD users vs almost half of the control group.5 So what if sperm survives these obstacles? Well, IUDs also have an adverse effect on ova with lower numbers of ova recovered in IUD users (39% vs 59%).6 So what if the sperm and egg do manage to meet up? IUD users had either no embryos at all (64%) or abnormal embryos (36%) vs 50% of controls with normal embryos, 35% abnormal embryos, or 15% with none.6 [Please note that these studies were performed in users of copper IUDs.] While I understand that this will probably always be a contentious issue due to socio-cultural-political interests, the scientific evidence continues to chip away at the persistent belief that IUDs are abortifacients.
Now let's switch our focus away from the more arcane deliberations regarding LNG-IUD mechanism of action to a very clinically relevant topic. When does this effect on cervical mucus occur? Many of us, including me, tell women that they should use a backup method or avoid sex for 7 days after LNG-IUD placement, theorizing that if they are mid-cycle, then this will be enough time to make sure they do not put themselves at risk for pregnancy. This same group of investigators looked at how rapidly the LNG-IUD effect on cervical mucus appears.7They placed LNG-IUDs mid-cycle with documentation of good quality (fertile) cervical mucus. Five of 6 subjects had poor quality mucus within 1 day. The remaining subject had poor quality mucus documented by day 3. Although very preliminary in nature, this incredibly detailed work might help us to better counsel women and allow women to return to their normal activities earlier without feeling guilty that they are going against our advice.
- Mishell DR. Intrauterine devices: Mechanisms of action, safety, and efficacy. Contraception 1998;58:45S-53S.
- Croxatto HB, et al. Treatment with Norplant subdermal implants inhibits sperm penetration through cervical mucus in vitro. Contraception 1987;36:193-201.
- Moghissi KS, Marks C. Effects of microdose norgestrel on endogenous gonadotropic and steroid hormones, cervical mucus properties, vaginal cytology, and endometrium. Fertil Steril 1971;22:424-434.
- Sagiroglu N. Phagocytosis of spermatozoa in the uterine cavity of woman using intrauterine device. Int J Fertil 1971;16:1-14.
- El-Habashi M, et al. Effects of Lippes loop on sperm recovery from human fallopian tubes. Contraception 1980;22:549-555.
- Alvarez F, et al. New insights on the mode of action of intrauterine contraceptive devices in women. Fertil Steril 1988;49:768-773.
- Natavio M, et al. Length of time after insertion of the levonorgestrel-releasing intrauterine system for it to significantly alter cervical mucus quality and sperm penetration. Fertil Steril 2010;94:S94.