I will use the phrase "using oral contraception" (and cognates) to abbreviate the complex state of affairs of being a woman of normal fertility and using standard contemporary (not the older higher dose pill) oral contraception as the only form of contraception for the period of at least a year while being sexually active at an average sexual frequency. The following argument is sound when implicitly conditionalized on the present state of medical knowledge and technology:
- Someone who prevents the implantation of an embryo that he or she is a parent of causes the death of his or her innocent child. (Premise)
- It is wrong to act in a way that carries a significant risk of one's causing the death of one's innocent child without very grave reason. (Premise)
- Using oral contraception carries a significant risk of one's causing the death of an embryo that one is a parent of. (Premise)
- It is wrong to use oral contraception without very grave reason. (By (1)-(3))
- Very grave reason to use oral contraception is exceedingly rare if it ever occurs. (Premise)
- It is wrong to use oral contraception except perhaps in exceedingly rare cases. (By (4) and (5))
The argument has a formal feature that complicates things. The terms "significant risk" and "grave reason" are not defined explicitly. Rather, they must be taken to be partially interdefined by (2).[note 1] Thus, in defending (5), one needs to argue that what is exceedingly rare is the sort of reason that would fit into the exception in (2), where "significant risk" is the risk we get from the medical literature supporting (1).
I will not argue for (1) and (2). I think (2) is uncontroversial, and (1) will generally be accepted by pro-life folks.
We do not know exactly how often the use of oral contraception causes a failure to implant. A survey of data is given by Larimore and Stanford (2000). Hormonal contraception has three main modes of operation according to references (including product inserts in at least some cases): (a) prevention of ovulation, (b) modification of uterine environment that makes it inhospitable, and (c) modification of cervical mucus to make it harder for sperm to reach the ovum. The data in Wildt, et al. (1998) strongly suggests that sperm can travel through thick mucus. So (c) isn't a very effective method. Studies show that ovulation still occurs in 1.7-65% of cycles (see Larimore and Stanford, 2000; unfortunately, I don't know if this is for perfect use or typical use). Assume, conservatively, a not unrealistic fertilization rate of about 10% per cycle in which ovulation occurs.[note 2] Assuming independence (which isn't exactly right, admittedly), this gives us an annual fertilization rate of 2%-55% (assuming 12 cycles per year). But the established pregnancy rate for oral contraception is significantly lower than most of this range (the perfect use pregnancy rate is 1% or lower; the typical use pregnancy rates are higher), where an established pregnancy is one where implantation has occurred. So there is good reason to think that there are probably significantly more fertilizations than established pregnancies, and hence there is good reason to think that using oral contraception carries approximately a 1% to 50% chance (this will be a combined epistemic and nomic probability) per year of preventing a fertilization, and thereby causing the death of the embryo.
This will yield (3), assuming 1% to 50% counts as "significant risk" in the sense used in (2). But I think it clearly does count. A quick way to see this is to imagine that the risk is not to one's child, but to the user. The FDA would not approve a form of contraception which had a 1% to 50% annualized chance of resulting in the death of the user, and medication with that fatality rate would only be approved if the condition it treated was very grave indeed. If such a risk to the user would be unacceptable absent a very grave reason, a fortiori it would be unacceptable when the risk was to another party.[note 3] In fact, I doubt that we would approve of life-saving medication that had a 1% to 50% chance of causing the death of a bystander (imagine that it gives off noxious fumes or something).
That leaves (5) to be argued for. But that's easy. Given that the "very grave reason" would have to be one that would justify taking an annualized 1% to 50% risk of being the cause of one's innocent child's death, it seems clearly that only extreme circumstances will yield such a reason. If using oral contraception is needed to save someone's life, a case might be made (though note the caution at the end of the previous paragraph). But remember that I defined "using oral contraception" as including sex at a normal sexual frequency and with no other contraception being used. So that would have to be a case where having sex at a normal sexual frequency was needed to save a life and no other contraception was possible. Maybe if a woman had to have sex with a dictator for a year or he else he would kill her (or someone else), and if pregnancy would result in the woman's death, and if the use of non-abortifacient contraception were impossible, this could be argued to be a case like that (in the end I deny it, because it is wrong to commit adultery even to save a life). But such cases are, indeed, exceedingly rare. Perhaps saving someone from serious disability would qualify. Could "saving a marriage" qualify? I doubt it. Would it be permissible for a couple to undergo a "marriage saving treatment" that had a 1% to 50% chance of killing one of their children? And the case would have to be such that the consequences of pregnancy would be very grave, and that no other contraception was possible. (And even then it would be wrong if, as I think, marital direct contraception is always wrong—but that requires a different argument.) So I think (5) is very plausible.