Is not the zygote what is considered the human being after the moment of conception? It is that first stage of development after the union of the sperm with the egg. So prevention of the blastocyst from implantation is an abortive action if you believe it’s human life after conception. Implantation is an important thing to be considering if you value human life. Even if one objects to the use of the IUD, implantation is what most forms of birth control work to prevent.
Most forms of oral or estrogen/progesterone birth control work by preventing ovulation, so there’s no oocyte to fertilize in the first place. They also act sort of like barrier methods in that they make the cervical mucus thick, so the sperm has a harder time getting into the uterus and on up to the fallopian tube, etc.
The arguments have been whether or not these make the uterine lining too thin for implantation. As I said, we had some elegant studies in the last 10-15 years showing that the effect of the corpus luteum overwhelms the effects of the birth control pill, patch, etc., if there’s ovulation.
After ovulation, the follicle (bubble or cyst) that contained the oocyte becomes the corpus luteum, a powerful hormone production site. These endogenous or natural hormones overwhelm the effects of the tiny amounts of the birth control pills, patches.
Some of the OCP’s and EllaOne definitely have post-ovulatory effects, however. The mini-pills slow the movement of the new embryo down the fallopian tube, increasing the risk of tubal pregnancy. EllaOne delays the progesterone surge and may interfere with the normal development of the placenta and “burrowing” at implantation.