This is a very sensitive and important topic.
When interviewed by Ira Flatow, Dr. Gemzell-Danielsson made many claims that are hard to believe. She says that Plan B “has no effect after ovulation, no effect on the fallopian tube or on the endometrium.” This is a false claim, as stated in the study below. There are at least small effects on hormones inside a woman’s body that promote an inhospitable environment for a fertilized ova.
Dr. Gemzell-Danielsson also claims: “When we did the study, there were two large multicenter, multinational trials, but the main outcome of those studies were efficacy and side effects. So mechanism of action was not involved in those trials. And to register the pill, it was not required to study the mechanism of action.” In this argument she seems to affirm that a side effect, which the FDA seems to have noted and published on the packaging, of Plan B is inhibiting implantation. The “mechanism of action” does not prevent implantation, but she infers that it is in fact a side effect. Then Flatow makes the faulty deduction that “the language was written before you even knew how it worked.” It’s not that they didn’t know how it worked but that there is a difference in studying the effects of the mechanism of action (which in this case will not affect a fertilized ovum) with the side effect it causes (which in this case seems that it can affect a fertilized ovum.) That at least appears to be the delineation they are making.
Below is an excerpt from a study that Dr. Gemzell-Danielsson could possibly be alluding to, though we don’t know because she never cited specific studies to support her argument.
Does Plan B Prevent Fertilization or Interrupt Fallopian Tube Function? No data are available on whether Plan B directly interferes with fertilization itself. However, since fertilization occurs in the fallopian tube, Plan B could indirectly prevent pregnancy by interrupting the transport of fertilized ova through the fallopian tube.
Does Plan B Impair Endometrial Structure or Physiology? In 2 studies relevant to this question, women who took Plan B at the time of ovulation underwent endometrial biopsy 8 to 9 days later, when implantation ordinarily occurs. The endometrium revealed either minimal or no changes in microscopic appearance or biochemical markers. Another study found diminished amounts of endometrial glycodelin A in some women who had received Plan B. Since glycodelin A may play a role in adhesion of the nascent embryo to the endometrial surface, such an effect could be a mechanism by which Plan B interferes with implantation. However, in this study endometrial glycodelin A was affected only in those women who took Plan B before the LH surge, a circumstance in which ovulation generally does not occur. The glycodelin A effect may thus be an epiphenomenon, the result of an absent or inadequate LH surge rather than a direct link in the causal pathway of contraception. More generally, it is not known whether any of the alterations in endometrial biology sought in these studies is actually capable of interfering with implantation.
The previous paragraph suggests that there is a possibility that Plan B interferes with implantation. One of the reasons this drug is so controversial is because it’s very hard to prove why a woman didn’t get pregnant. Was it natural or induced?
Later in that study there is this paragraph, which seeks to reinforce that Plan B does not inhibit implantation.
What Does the Timing of Plan B's Effectiveness Reveal About Possible Interference With Postfertilization Events? If Plan B interferes with implantation, it should be capable of preventing pregnancy when it is used after fertilization. In a recent clinical study in which timing of ovulation was determined quite precisely using hormonal criteria, no pregnancies occurred in the 34 women who had unprotected intercourse on days –5 to –2 (day 0 being the day of ovulation) and took Plan B (1.5 mg as a single dose) before or around the time of ovulation; 4 or 5 pregnancies would have been expected in this group if they had not used the drug. In contrast, 3 pregnancies occurred among the 17 women who had intercourse around days –1 to 0 and took Plan B on day +2; 3 or 4 pregnancies would have been expected had they not used the drug. Although the results of this study need to be confirmed and extended, they are consistent with epidemiological evidence on the efficacy of emergency contraception in relation to the timing of ovulation and are directly contrary to what would be expected if Plan B interferes with implantation.
If Plan B interferes with implantation, its efficacy should not decrease with short-term delay in use as long as it is taken just before or during implantation.
The study cited above (with the 34 women) is not extensive enough to prove Plan B never affects implantation. Gene Rudd, MD in his response to an MSNBC Article on the morning after pill says “Post-fertilization effects are necessary for these products to be effective as claimed. There is either deception about how they work, or how well they work.”
Since there is no way to prove exactly what is preventing women who take Plan B from getting pregnant, the best course of action is to consider the consequences and make an informed decision. It is possible to take Plan B and not have it terminate a pregnancy. It is also possible to take Plan B and terminate the pregnancy. Personally, I never want to take a pill that could have abortifacient affects because participating in the destruction of a human life that was created by God is something I definitely want to avoid.
