Although the authors make a point to redefine pregnancy as beginning at implantation, this article contains an otherwise fair review of the “Mechanisms of Emergency Contraception Pills,” from the August issue of the journal, Contraception.
Please note this paragraph:
Early treatment with ECPs containing only the progestin levonorgestrel has been shown to
impair the ovulatory process and luteal function;16,17,18,19,20 no effect on the endometrium was
found in two studies,17,18 but in another study levonorgestrel taken before the LH surge altered
the luteal phase secretory pattern of glycodelin in serum and the endometrium.21 Treatment with
ECPs containing only levonorgestrel during the peri-ovulatory phase may fail to inhibit ovulation
but nevertheless reduce the length of the luteal phase and total luteal phase LH concentrations;
this observation suggests a post-fertilization contraceptive effect.16 Levonorgestrel also interferes
with sperm migration and function at all levels of the genital tract.22 Studies in the rat and the
Cebus monkey demonstrate that levonorgestrel administered in doses that inhibit ovulation has
no post-fertilization effect that impairs fertility.13,23,24 Whether these results can be extrapolated
to women is unknown.
The articles referred to in the article mention ovulatory dysfunction and that LH change affects the release and movement of the oocyte. This function prevents fertilization, and is a true contraceptive effect, not one of those redefined definitions of contraceptive.
Please email me if the link stops working. I have the article, and will do the work, if necessary.