What percentage of fertilized eggs fail to implant in the uterus?

Question

Could you provide sources if you have them (preferably not christian/atheist propaganda blogs)

Answer 1

If I recall correctly, because this is difficult to study in humans, the best estimates come from studies on other primates - and my recollection is that in chimpanzees, about 70% of conceptions fail to come to term.

That said, according to the article in Discover at the link below, estimates as of 2004 are that 60 - 80% of conceptions don't implant. The article also mentions the New England Journal article cited by the answerer above, but says that tha data showed that 31% of conceptions _that had already implanted_ failed to come to term.

I think an additional 2-5% of live births have identifiable birth defects.

The whole process is so complicated, I guess it is no great surprise that errors and failures are common. I don't know how religious conservatives would spin this data.

Another twist is that on rare occasions, two blastocysts can fuse to form a single embryo, sort of like fraternal twins who are melded into a single body = that person will have been made out of 4 gametes. Again, I think this might be a difficult thing for religious conservatives to address = does such a person actually have two souls since they are derived from two conceptions?

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Here is the abstract from the NEJM article = they are clearly talking about detecting the pregnancies at or after the time of implantation.

N Engl J Med. 1988 Jul 28;319(4):189-94
Incidence of early loss of pregnancy.

Wilcox AJ, et al.

We studied the risk of early loss of pregnancy by collecting daily urine specimens from 221 healthy women who were attempting to conceive. Urinary concentrations of human chorionic gonadotropin (hCG) were measured for a total of 707 menstrual cycles with use of an immunoradiometric assay that is able to detect hCG levels as low as 0.01 ng per milliliter, with virtually 100 percent specificity for hCG in the presence of luteinizing hormone. Our criterion for early pregnancy--an hCG level above 0.025 ng per milliliter on three consecutive days--was determined after we compared the hCG levels in the study group with the levels in a comparable group of 28 women who had undergone sterilization by tubal ligation. We identified 198 pregnancies by an increase in the hCG level near the expected time of implantation. Of these, 22 percent ended before pregnancy was detected clinically. Most of these early pregnancy losses would not have been detectable by the less sensitive assays for hCG used in earlier studies. The total rate of pregnancy loss after implantation, including clinically recognized spontaneous abortions, was 31 percent. Most of the 40 women with unrecognized early pregnancy losses had normal fertility, since 95 percent of them subsequently became clinically pregnant within two years.

Answer 2

It was reported in 1988 that 25 percent of fertilized eggs fail to survive six weeks, so early that most mothers did not know they had been pregnant (New England Journal of Medicine, 1988, 319, pp 189-94). The implantation of the fertilized egg in the wall of the uterus is necessary for the nourishment and growth of the fetus. The lost fetuses tend to be those that implant late.

Answer 3

Something like 80%, but I can't back it up. I believe there's also about a 50% spontaneous abortion rate of implanted embryos, but again - can't back it up.

Good gawd, we're fragile bags of meat. How did we ever make it out of the trees?