In a 2000 article in the Archives of Family Medicine, Larimore argued that because the extremely high effectiveness rate of hormonal contraception is much higher than what one would expect on the basis of its often not very high rate of ovulation suppression, there is very good reason to think a significant portion of the high effectiveness rate is due to preventing implantation of the early embryo. But many women believe that the early embryo is a human being, and hence would take this effect to be a morally unacceptable abortion (and I expect there are additional women who do not take the effect to be utterly morally unacceptable, but for whom such an effect is nonetheless a significant reason against the use of the contraceptive method). Since patient autonomy requires that the patient be informed of those aspects of treatment that are salient given the patient's values and moral beliefs, the physician's duty in the case of such women is to inform the women of the risks of prevention of implantation. Because a physician may not know whether a particular woman consider this factor relevant, Larimore suggests that a physician can say something like: "Most of the time, the pill acts by preventing an egg from forming. This prevents pregnancy. However, women on the pill can still sometimes get pregnant. Some doctors think that the pill may cause the loss of some of these pregnancies very early in the pregnancy, before you would even know you were pregnant. Would knowing more about this possibility be important to you in your decision about whether to use the pill?"
Even bracketing the question whether contraception and abortion are morally permissible, Larimore is right about what is required what the current consensus on patient autonomy and informed consent. I've had a look at the titles and often abstracts of the 55 papers listed as citing Larimore's, and surprisingly none of them appears to be an argument to the contrary (though maybe some contain such an argument in their body). One interesting recent study of women in Western and Eastern Europe found that only 2% can correctly identify all the mechanisms of oral contraceptives and the IUD (for which the postfertilization effect is probably even greater), but that 73% said that their healthcare provider should inform them about effects that occur after fertilization even when these effects are before implantation. So not only is the information salient to many women, it is information that many women want.
It seems to me that pro-choice physicians should be impressed by the need to obtain informed consent for such postfertilization effects insofar as a significant part of the reasoning for the pro-choice position involves considerations of women's autonomy.