Ales Rarus

A handy reminder of the general order of hormones related to fertility is the acronym FELOP, which stands for

1. Follicle Stimulating Hormone (FSH)
2. Estrogen (E1, E₂, E₃ = estrone, estradiol, estriol)
   
3. Luteinizing Hormone (LH)
   
4. Ovulation
5. Progesterone (P,P₄)
   

Before looking at the most recent salient research, let's examine a couple oft-sited peer-reviewed literature reviews. The first, Postfertilization Effect of Hormonal Emergency Contraception (Kahlenborn, Stanford, and Larimore, 2002), is often cited by pro-lifers as presenting evidence that Plan B is abortifacient.

The question as to whether hormonal EC sometimes acts after fertilization to prevent implantation, called a postfertilization effect (i.e., early abortion), is important and could have far-reaching implications given the differing attitudes in regard to its use and related issues such as informed consent, emergency department rape protocols, and conscience clauses. Postfertilization effect refers to any effect that reduces the survival rate of the zygote/embryo after fertilization, usually prior to clinical recognition of pregnancy. We use the term early abortion synonymously with postfertilization effect. We recognize that some physicians,⁴ geneticists, and ethicists have arbitrarily defined human life as beginning after implantation, thereby eschewing the possibility of an early abortion prior to implantation. However, we recognize the traditional definition of pregnancy: “the gestational process, comprising the growth and development within a woman of a new individual from conception through embryonic and fetal period to birth,” where conception is defined as “the beginning of pregnancy, usually taken to be the instant that a spermatozoon enters an ovum and forms a viable zygote.”⁵

A someone who believes that life begins at conception, I'm in agreement with this motivational introduction. However, its obvious bias and polemical tone does make me a little uncomfortable from an objective scientific viewpoint. Moving on:

In a previous review⁶ of the mechanism of action of [oral contraceptives, OCs], we concluded that they act at times via a postfertilization effect, that is, after fertilization and prior to the clinical recognition of pregnancy. However, the Yuzpe regimen and Plan B have a different dose and time course for use, which may result in different actions on the reproductive system. This article reviews data on the use of the Yuzpe regimen and Plan B with regard to their mechanisms of action and any potential ethical implications of those mechanisms.

That's as far as you're going to read from that paper on this blog. The authors consistently refuse to disambiguate the Yuzpe regimen (a mix of ethinyl estradiol - an estrogenic hormone - and levonorgestrel - a synthetic progestogen) and Plan B (levonorgestrel alone). Consequently, since both are forms of EC, any evidence that Yuzpe might be abortifacient is implied to damn Plan B as well. Their earlier literature review of OCs that they cite suffers from a similar "guilt by association" approach. Since the effects of LNG are not presented clearly, separate from those of the Yuzpe regimen, this review only serves to add confusion and misunderstanding to the current discussion. Were it not for its frequent citation by various members of the pro-life movement, I would not mention it at all. On the other hand, the end of the article includes some good points about informed consent that are worth reading. However, though interesting, they are not directly relevant to this review.