Oh yeah, you two love science. I can provide plenty of more sources that are in this range.
http://www.bioethics.gov/transcripts/jan03/session1.html
PROF. SANDEL: Thank you. I have two questions about the rate of natural embryo loss in human beings. The first is what percent of fertilized eggs fail to implant or are otherwise lost? And the second question is is it the case that all of these lost embryos contain genetic defects that would have prevented their normal development and birth?
DR. OPITZ: The answer to your first question is that it is enormous. Estimates range all the way from 60 percent to 80 percent of the very earliest stages, cleavage stages, for example, that are lost.
PROF. SANDEL: Sixty to 80 percent?
DR. OPITZ: Sixty to 80 percent. And one of the objective ways of establishing the loss at least as of the moment of implantation, well, even earlier, let's say as of five days because the blastocyst begins to make a chorionic gonadotrophin and with extremely sensitive assay methods, you can detect the presence of gonadotrophins, let me say, first around Day 7. That's the beta of human chorionic gonadotrophin. And if you follow prospectively the cycles that has been done on quite a few occasions in the Permanente study in Hawaii and so on, a group of women, of nonfertility, who want to conceive and you detect the first sign of pregnancy there of human chorionic gonadotrophin, about 60 percent of those pregnancies are lost.
It is independently corroborated by the fact that the monozygotic twin conception rate at the very beginning is much, much higher than the birth rate and then if you follow with amniocentesis, the presence of the two sacs in about 80 percent of cases,the second sac disappears, one of the sacs disappears.