"If you want to search the primary literature, try medline(pubmed). They have many articles for your perusal. Of course, all the research you are going to see is regarding implantation rates of fertilized eggs that are being artificially introduced to the mother. Not really what you're looking for, but its the best that you're going to get. Remember that these people are infertile in the first place, and will have a much higher probability of having lower implantation rates."
Thank you, yes - this 80% figure just seems too high, but it makes sense that studies would be done with the couples struggling with fertility.
So really in the end...we don't know what the rate really is - and this 80% number gets bandied about to justify using hormonal contraception/abortificants.
----"and this 80% number gets bandied about to justify using hormonal contraception/abortificants."-----
People are very intelligent and they can use all sorts of logical game playing, including yours truly, to justify sinful behavior. This is our nature. While biblical truth(and scientific truth to a much lesser extent) can be used to demolish these arguments, the word tells us that the people wielding these arguments really aren't fooling themselves..... they KNOW that they are committing sin. As to degrees of sin.... I know that each and every sin is capable of sending a soul to everlasting punishment..... but human killing...... I imagine the consequences are grave.