------"How do they know how many zygotes they are dealing with and how do they know they are being flushed away?"-------
Not sure about THIS study. I know that various methods of IVF(In Vitro Fertilization) boast different pregnancy rates in those who've experienced repeated implantation failures. The numbers here are from a population of people who have struggled with having children and are more likely to have more implantation failures. Certain methods boast implantation rates of somewhere in the range of 15 - 20 percent with this population of people.
Within normal populations, it is very invasive to try and capture all material exiting the vagina for a month's period of time, and examine it under microscopes to determine whether a zygote was flushed. Implantation rates are really hard to come by 'in the wild'. Still, they really vary between people.... as you were saying scotswife, you are one fertile woman. I would imagine your implantation rate is MUCH higher than 20 percent.
Here we have a scenario where it makes sense to think of the Lord opening and closing the womb. Some people are going to have varying levels of fertility.
Normal implantation rates should be somewhere in the 75 percent range or higher. There are many other factors that lead to ultimate pregnancy, so the implantation is not the only stopping point.
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.
"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.