I ran that doctor’s email by William Hurlbut before posting it. Here’s his response:
I would say that, over all, [the doctor] is scientifically accurate and conceptually (no pun intended) accurate—impressively so. But the central question . . . [is] what is or isn’t rightfully called a human being. This is, to some extent a definitional question, but also a theological question that might reflect on the depth of the fall of nature [or] the benevolence of God—the latter, I think, should not be called into question by whatever is decided on the scientific plane.
The figure of ‘embryo attrition’ of 60-80% is, as [the doctor] explains, an extrapolation and interpretation from medical experience and scientific evidence. The fact that teratomas and hydatiform moles can induce the changes in hormonal levels is a clue that you don’t have to be a human organism to do so: therefore many other ‘failures of fertilization’ that are capable of partial and incomplete development might also appear to be genuine conceptions and pregnancies. For example, trisomies of chromosome #1 (the largest chromosome) do not implant. . . . The point is that Sullivan is using the term embryo too loosely, and [the doctor] doesn’t seem to be worried about discerning the moral category, just the medical prognosis.
How do we know the percent of apparent fertilizations that fail, forming something that isn’t reasonably called a human conception? There is a paper that looked at the medical side of this—I believe it is cited in one of our PCB reports—that used that statistic, and it has mostly been perpetuated from that study I think. I vaguely recall another paper that actually looked at the uterine linings of post surgical hysterectomy uteri and discerned the % of implantations. But, Ross does not cite another source of evidence, and that is IVF itself. Though these statistics may not be accurate for the embryos of fertile couples, there is a growing body of evidence about the genetics and developmental prospects for what IVF produces.
Studies show that on average only about half the eggs from superovulation will actually fertilize (not surprisingly since they are in varied states of maturity), of those only about a half or a third look normal (those with heavy ‘fragmentation’ or other grossly evident abnormalities are not clinically implanted), of those that do form normal looking embryos it appears that 20-60 percent (depending on maternal age) will be shown to have aneuploidies such as trisome 21 (the smallest chromosomes by the way, with the fewest genes—which may explain why they sometimes make it to birth and beyond). Beyond that, in spite of all the visible inspection and careful procedural nurture, even in the best cases only around 35-50% of implanted IVF embryos make it to term.
What is the moral meaning of all this? I’m not quite sure; there is a range of scientific meaning, so a range of moral meaning. For one thing, I (and
others) doubt that the high rate of failure of fertilization is generalizable. Those using natural family planning report a higher rate of successful pregnancy than you would expect if 60-80% of conceptions fail. Likewise, [the doctor] has rightly reported that 1/6 or so recognized pregnancies end up as spontaneous abortions. But many women go through all their pregancies without a miscarriage.
Still, most sexually active women report occassional unexplained delays in getting their periods . . . so it is reasonable to assume that many, many fertilization events lead only to non-viable, non-human organic trajectories. But, I guess it depends on whether David Prentice or Germain Grisez gets to define ‘human.’ I disagree with Sullivan’s difinition: “A zygote is the very first entity that can be called human life: it’s the speck containing 46 chromosomes that exists the moment after conception.”–or at least the definition he ascribes to the new advocates of natural law that implies every such construction qualifies as fully human. Clearly some combinations of 46 chromosomes are not human beings: teratomas and hydatiform moles and many other inadequately constituted conception attempts.
. . . . [M]any ‘zygotic’ formations would never even evoke the changing hormonal signals that indicate pregnancy. They would be so fundamentally failed that they might not even divide or divide a few times and then cease to grow. . . .
So, the key question of how many ‘fertilization products’ do not form babies is a difficult one to answer, but the answer clearly is many, perhaps 60-80%. The question of how many of these are reasonably not called human ‘zygotes’ or ‘embryos’ is a definitional problem, but there again, I would think it is a large number, perhaps a half or more of the first number.
Here, in case you’re interested, is a statement on this matter from Grisez:
“Moreover, in the actual examination of the results of one thousand spontaneous abortions, Dr. Hertig found 48.9 percent with absent or defective embryos, most with no embryonic mass at all. If these specimens already were causally determined to be so at the time of fertilization, it seems doubtful whether we should say that a human life was lost, or merely that a fertilization occurred from which no individual ever could have developed.” (p32 Abortion: the Myths, the Realities, and the Arguments).
Many thanks to Dr. Hurlbut as well.