Postfertilization effects of birth control methods

In considering options of which birth control method to use, couples have a variety of factors that they may consider. See prior discussion at Times & Seasons here.

Among the information that couples need are the medical facts about contraception, including effectiveness, side effects, and mechanism of action. Why is mechanism of action an important consideration?

Different birth control methods may act at different stages of the reproductive cycle. While most birth control methods act before fertilization, some birth control methods may also have secondary effects after fertilization to prevent a clinically recognized pregnancy (a secondary postfertilization effect). Such effects could include direct killing of the embryo, or creating an inhospitable uterine environment for implantation and maintenance of the pregnancy. While some authors have called this an abortifacient effect, other authors have objected that because pregnancy has been defined to begin at implantation (a new definition that is not universally accepted in medicine or science), an “abortion� or “abortifacient� effect can operate only after implantation. The term “postfertilization effect� identifies this issue of interrupting early human development unambiguously without eliciting controversy based purely on competing definitions of the beginning of pregnancy. Regarding the definition of pregnancy, see

National opinion polls suggest that many women (about half) believe that “human life begins� at fertilization regardless of whether pregnancy is defined by medical experts to begin at fertilization or implantation.
For these women, a birth control method that could act after fertilization may conflict with personal moral and religious beliefs. As a result, these women may wish to refrain from using birth control methods that may exhibit a postfertilization effect.

We have recently published a study showing that a large percentage of female patients in Utah and Oklahoma are concerned about this issue and make their choices of birth control methods in accordance with their beliefs about which methods do not have a postfertilization effect:

Which methods of birth control have postfertilization effects? Here’s where it gets a little bit fuzzy. Other than abortion (including very early medication-induced abortion or “menstrual regulation� with RU-486 or mifepristone or other drugs), there is probably no method of birth control that operates mainly through postfertilization effects. Oral contraceptives (“the pill�) prevent ovulation most but not all of the time. However, there is medical evidence (but not absolute proof) that oral contraceptives have a postfertilization effect at least some of the time. How often they work this way is completely unknown. Postfertilization effects are more likely for the progestin-only pill (the “mini-pill�), or when “the pill� is not taken consistently, i.e., doses are missed. We have reviewed the evidence:

The intrauterine device (IUD) prevents sperm migration through the uterus most but not all of the time. There are data on fertilization rates in women with the IUD, such that estimates can be made as to how often an embryo that has been formed dies as a result of the presence of the IUD. This ranges from 0.2 to 2 embryo losses per woman wearing an IUD per year.

Emergency contraception (“the morning after pill�) prevents ovulation much but not all of the time. We estimate that when emergency contraception prevents clinically recognized pregnancy, it does so by a postfertilization effect somewhere between 10-50% of the time.

Only when women are educated about the mechanisms of action of birth control methods can they make a fully informed decision in the process of birth control selection. Informed consent can be explained as the right and ability of individuals to determine their own goals based on their own values and to decide how they will achieve these goals they have established. A woman should be provided such information to determine her own goals in choosing birth control methods that are in harmony with her own beliefs and values. Not providing available information concerning postfertilization effects to women who consider this information important is a violation of informed consent. If moral or religious beliefs relating to when human life begins in relation to postfertilization effects are important to some women, as our research has documented, then it is their right to make a decision whether or not to use a birth control method that may exhibit such effects. Without such information, patients are denied the opportunity to make an informed decision.

6 comments for “Postfertilization effects of birth control methods

  1. From another thread:
    “After reading this article, I came to the conclusion that the reason Dr. Stanford doesn’t support the pill is because it has the potential to prevent implantation of fertilized eggs. I had heard this before- apparently it prevents ovulation most of the time, but when ovulation occurs anyway and fertilization occurs, implantation is not possible. That is contradicted by this Christian website, which discusses the issue and how it relates to various kinds of contraceptives, including several hormonal contraceptives:”

    To make a very long story short-
    1) It is true that oral contraceptives used very consistently very rarely allow “escape” ovulation, but to say that they never do is simply wrong. Otherwise the pregnancy rate would be zero during perfect use, and it’s not.
    2) The paper Walt Larimore and I published on this topic, has, in my judgment, never been refuted, although a number of Christian websites (not peer-reviewed scientific publications) have put forth rebuttals. It often boils down to the assertion that one cannot definitively prove that postfertilization effects occur with use of the pill. That’s true. But neither is there proof that they do not. In my judgment, the weight of evidence is that they do. (Incidentally, ovulation is most profoundly suppressed and postfertilization effects are probably most rare with depo-provera, the 3-month shot, except perhaps during the extended time period that the woman is coming off of the medication.)
    3) I have been involved in many discussions with professional colleagues about postfertilization effects of oral contraceptives. Physicians and scientists who are “pro-choice” and are not concerned about abortion almost never object. These mechanisms of action are not something new. They are listed in every standard pharmacology textbook and in the FDA-approved package insert for physicians for oral contraceptives, the Physicians’ Desk Reference, etc., (but not in the package inserts for patients). The physicians who end up voicing the most strenuous objections to the idea that oral contraceptives might have postfertilization effects are almost always pro-life Christian physicians who prescribe them. That is generally who you will see putting information on the websites making the kinds of assertions you noted in your post.

  2. One thing I will say is this–my own experience with doctors leads me to believe that Dr. Stanford is right that doctors usually don’t discuss the ins and outs of a lot of their recommendations well. Its not because they’re evil, but there it is. Sara and I found that when we pressed the doctors with lots of open-ended questions and follow-up questions, are initial impression about what would be the right choice for us to make often changed.

  3. “It is true that oral contraceptives used very consistently very rarely allow “escapeâ€? ovulation, but to say that they never do is simply wrong. Otherwise the pregnancy rate would be zero during perfect use.”

    I hadn’t considered that before… thanks for the clarification.

  4. After six children, and complications with varicose veins, I decided to do something semi-permanent. My OB is LDS, and has done significant research on copper IUDs. He told me that studies done on women who were going to have tubal ligations suggest that the copper works pre-conception: The copper IUDs were inserted pre-surgery, and the women had intercourse within a specific time frame. When the tubal surgery was performed, the surgeons “harvested” any sperm in the fallopian tubes at the time. According to my OB, the number was zero, suggesting that the copper is fatally inhospitable to sperm. Furthermore, the string that slips through the cervix causes the cervix to thicken, and making it more difficult for sperm to enter the uterus in the first place. In any case, my doctor told me, “If it were an abortant, I wouldn’t use it.”

    I looked at the link you provided, and didn’t see any specific data, though the abstract did seem to support what my doctor said about copper IUDs.

    Thank you for this series.

  5. this American Assoc of pro-life OBs article was very useful to me in making my own judgement call on this issue, which concerns me greatly. We have thus far found every method of brtrh control to be unacceptable, but reading this did curb my rejection of hormonal methods.
    we’ve just gone without borth control for 4 years now ( 2 kids and 3 miscarriages). Before that, we used NFP for 3 years. I also tried the pill, depo, condoms and spermicides as a nonmember teen!

  6. From cchissyy’s link: “In a normal menstrual cycle, on the day of ovulation the uterine lining (proliferative endometrium) is not receptive to implantation. Seven days of follicle and corpus luteum hormone output transform it to “receptive.” The same follicle and corpus luteum hormone output, when ovulation occurs in a “pill” cycle, should have a similar salutary effect on the pill-primed endometrium… It is highly probable that the so-called “hostile to implantation” endometrium– heralded (without proof) from the beginning by the “pill” producing companies, echoed (without investigation) by 2 generations of scientific writers, and now adopted (as a scientific fact) by some sincere prolife advocates– simply does not exist six days after ovulation in a pill cycle.”

    This is interesting, but I have no way to know whether it’s true. Dr. Stanford?

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