There’s a useful survey article related to early chemical abortions at the Presbyterian pastors blog Bayly Blog which points out that:
. . .
Midway through the twentieth century, the western world underwent a sea-change on birth control. Courts reversed laws prohibiting its distribution (see this summaryby Margaret Sanger’s grandson), churches reversed their historic condemnation of birth control with Anglicans leading the way, and physicians put their shoulders to the project by changing one small definition, hoping thereby to solve some tender souls’ conscience issues.
It’s this change in definition that’s critical to our understanding of what’s happening with medical abortions today.
In September of 1965, the American College of Gynecology (now the American College of Obstetricians and Gynecologists) issued a bulletin containing an edict that its members were to reverse their terminology concerning conception and pregnancy. Up to that time, everyone agreed conception (and therefore, pregnancy) occurred the moment the ovum was fertilized. Here’s how a 1963 U.S. Government public health pamphlet stated the matter:
All the measures which impair the viability of the zygote at any time between the instant of fertilization and the completion of labor constitute, in the strict sense, procedures for inducing abortion.
Then, by fiat ACOG changed the definitions:
[I]n 1965, American College of Gynecologists, a long-standing supporter of abortion and family planning, issued a medical bulletin that sought to change the accepted definition of “conception” from union of sperm and egg to implantation: “Conception is the implantation of a fertilized ovum [egg].” (from Americans United for Life, the legal arm of the anti-abortion movement)