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From Richard Dawkins on Feb 1, 2019

How could I have failed to predict it? My tweet of the beautiful newt embryology film is already triggering the abortion nuts. Did you know, at least 30% of human embryos are spontaneously aborted? Does that make God the world’s leading baby killer?

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    Deleted numerous comments. Let's leave religious/philosophical position on life and abortion out of this site, thanks. – Sklivvz Feb 2 at 20:28
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    Again, deleted comments from people that don't like Dawkins. Be nice, be constructive or just don't comment. – Sklivvz Feb 4 at 22:42
  • This question is already answered here at this closely related question: skeptics.stackexchange.com/a/17061/5337 – gerrit Feb 6 at 15:50
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    Rolling back to previous version as the edit clearly conflicted with the author's intention. – Sklivvz Feb 7 at 15:23
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Trivially true, yes. It's more commonly called Miscarriage:

Among women who know they are pregnant, the miscarriage rate is roughly 10% to 20%, while rates among all fertilisation is around 30% to 50%.

If one includes failure of a blastocyst to implant in the uterine lining, the total number of "abortions" can be as high as 60%:

A recent re-analysis of hCG study data concluded that approximately 40-60% of embryos may be lost between fertilisation and birth, although this will vary substantially between individual women.

  • I thought a more commom accepted value was 15% (No reference, but that was given in a human genetics course I attended---and where it was a topic) – kjetil b halvorsen Feb 2 at 11:09
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    It may be worth noting that the term "spontaneous abortion" is commonly used for miscarriage in medical settings. See, for example, this Merck Manual entry, – 1006a Feb 4 at 5:13
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    @1006a conversely many (especially older) legal texts concerning abortion use the term miscarriage. For a long time miscarriage and abortion where completely synonymous. The lay convention of using abortion solely of induced cases and miscarriage solely of spontaneous cases is relatively new. – Jon Hanna Feb 4 at 16:01
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    +1 as a side note: 1. It's a hard number to estimate because first weeks miscarriages can be mistaken as a normal period, the woman can not even have a clue about being pregnant at all. 2. It's also depends on environmental factors, those rates can be a worst at underdeveloped countries (I can like to see those numbers placed in the correct place and time frame) – jean Feb 4 at 17:49
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    @MichaelW., from a brief perusal of Dawkins' own website, it appears as though he doesn't distinguish between an embryo and something else during early human development. – elliot svensson Feb 4 at 22:12
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For those pregnancies that have already lasted 5 weeks, recent research sets an upper limit on the American public's cumulative "spontaneous abortion" of 22%, presenting the rate as a range from 11% to 22%.

The cumulative risk of miscarriage for weeks 5 through 20 of gestation ranged from 11 miscarriages per 100 women to 22 miscarriages per 100 women (11-22%).

A systematic review to calculate background miscarriage rates using life table analysis. Ammon Avalos L1, Galindo C, Li DK., 2012

Since it is unknown how many human beings die below a gestational age of 5 weeks, the best that researchers can do is to provide an extrapolated range, including such scientific methods as calculating bootstrap confidence intervals to account for data that's just plain missing from the study.

Early embryo mortality in natural human reproduction: What the data say Gavin E. Jarvis

How many human embryos die between fertilisation and birth under natural conditions? It is widely accepted that natural human embryo mortality is high, particularly during the first weeks after fertilisation, with total prenatal losses of 70% and higher frequently claimed. However, the first external sign of pregnancy occurs two weeks after fertilisation with a missed menstrual period, and establishing the fate of embryos before this is challenging. Calculations are additionally hampered by a lack of data on the efficiency of fertilisation under natural conditions.

...natural human embryo mortality is lower than often claimed and widely accepted. Estimates for total prenatal mortality of 70% or higher are exaggerated and not supported by the available data.

Even so, the critical review published concurrently with Jarvis' paper has this to say about his findings:

An ideal future investigation of fetal wastage is easy to imagine: daily assessment of EPF and hCG for a cohort of women attempting to get pregnant. Easier said than done! Consider what such a study would require: a reliable assay for EPF, the enrollment of thousands of women, collection of and accurate assessment of thousands of samples, and more. Perhaps these technical and logistical barriers can be overcome soon. In the meantime, we can recognize that there is strong circumstantial evidence that human fetal wastage is likely between 50 and 75%. At the same time, we can recognize along with Dr. Jarvis that this conclusion lacks definitive proof and that additional investigations and scrutiny are needed.

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    "It is unknown how many human beings die below a gestational age of 5 weeks." - this is pretty important for assessing your 11-22% rate. The 11-22% rate in your source is not <=20 weeks as suggested by the table, but rather 5-20 weeks. The discrepancy with the other answer and with Dawkins claim is that they are estimating the <5 weeks rate. By saying "at least 30%" Dawkins is hedging his statement on the lower estimate of the rate that includes those <5 weeks. – Bryan Krause Feb 1 at 20:33
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    I don't see this as a refutation of the Wikipedian numbers - your cited study covers only women who were aware they were pregnant and subsequently miscarried, which slots neatly into the "10-20%" for that subgroup as stated by Wikipedia. – jdunlop Feb 1 at 20:35
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    The sciencedirect article you link is actually their article on the paper I linked as my second source for my answer. :) – jdunlop Feb 1 at 21:15
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    Re "...how many human beings die below a gestational age of 5 weeks...", it seems that you're trying to bring in a different and quite controversial question. Quite a few people would say that no human beings die prior to that age. – jamesqf Feb 2 at 3:26
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    @James In context (Dawkins' claim), the voice is that of an extreme pro-lifer, those that believe humanity is naturally endowed at conception. Such people, according to Dawkins, have to blame God for all the spontaneous abortions. Going outside of that to discuss the logic of Dawkins claim (which is off topic here anyway) would be counter-productive. In other words, sticking to the language and definitions of the claim is appropriate here and has actually introduced nothing. – fredsbend Feb 4 at 23:20

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