Uhhhh...
You do realize that the author stipulated the pro-life definition of when life begins:
Even using religious conservatives' definition of when life begins—the moment an egg is fertilized—
Sadly, the medical definition of the beginning of pregnancy leaves a gaping hole that allows a lot of lives to be lost.
99.9999999999999% of pro-life people say that life begins at the moment of conception (fertilization). There is a logic to this: chromosomes from the male gamete fuse with chromosomes from the female gamete to produce an entity with a chromosome pattern that is distinctly different than either. That's why we define the beginning of life to this point (at any point prior, the gametes are simply part of the parents).
The problem is that one of the mechanisms of action of any hormonal contraceptive (as well as a copper IUD) is that it does not allow implantation. Therefore, according to the medical definition of pregnancy, a pregnancy has not been terminated (as a pregnancy has not happened yet). However, an abortion did occur.
Abortion: In medicine, an abortion is the premature exit of the products of conception
Source, Source, Source, Source.
If a baby is mature enough so that he/she would be classed a "fetus" or "embryo", then it is fairly obvious. If a baby is so immature as to be a zygote or blastocyst (i.e., before implantation), the premature exit of the zygote or blastocyst would still be an abortion, as that would be the product of conception.
(Note: "abortion", by itself, is a morally neutral term. "Induced abortion" is another thing altogether)
Yes, I read the article and saw that the author provided one interpretation of a pro-life definition of when life begins. The author did not seem to share that interpretation. It is not necessary to share that interpretation to be pro-life. Since my experience in medical research has given me the opportunity to observe countless millions of living human organisms that are not human beings first hand, my interpretation of what is a human being does not incorporate conception. Since we all experience the world through the processing of information in our brains, I think that the presence of a brain is crucial to the definition of a human being. Although brain cells only start forming about 3 weeks after conception, I think that using the definition of pregnancy--the implantation of the blastocyst--provides a perfectly good start point for granting legal protection to the embryo.