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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?
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.
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%).
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.
