Fetal Development Milestones: Objection and Response

by Jay Johansen
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We recently received an e-mail criticizing us for being inconsistent in some of our statements about milestones in fetal development. For example, the writer points out, in one article we say that the heart begins to beat at 18 days, while in another we say 25 days. Then he cites a book on fetal development which says this happens at 3 weeks.

And so, he concludes, "I highly recommend that you find a non-biased and RELIABLE source and make the corrections to your web page immediately. It's mistakes (is it really a mistake?) like these that cast a large shadow of doubt on pro life organizations such as yours. I truly hope that these are GENUINE mistakes and not an attempt to fool or mislead a reader."

Let me first reply to the accusations of deception, and then discuss the substantive, factual issues raised.

The Accusations of Deception

When we get criticisms like these, I normally brush off the comments like "are these really innocent mistakes or are you trying to fool and mislead people" and just answer the substantive points. But perhaps it is worth replying to this.

Reality is often complex. Very often, seemingly simple questions -- like "When does the unborn baby's heart begin to beat?" -- cannot be simply and easily answered. The more knowledgeable the expert, the more likely he is to give carefully qualified answers, "Well, one experiment indicates this, but another indicates that, and it depends on your exact definitions, and some researchers say that all our experiments are invalid because etc etc." The fact that someone cannot answer any question in ten words or less is hardly proof that he is stupid or a liar. Quite the contrary. If someone really was going to bluff or lie and simply make up an answer which he found convenient to his purpose, it would be easy to just state a number and stop there. If we were really trying to spread some lie about fetal development, surely the easiest thing in the world to do would be to pick one number and quote it consistently.

Indeed, to accuse us of deliberately misleading people over something like this is surely ludicrous. Does anyone seriously believe that if we convinced the world that the unborn baby's heart begins to beat at 18 days, when in reality this didn't happen until 21 days, that such a deception would have any impact at all on the abortion debate? Are there really people out there who say, "I think it's okay to abort a 16-week old baby if his heart has only been beating for 13 weeks, but wow, if his heart has been beating for 13 and a half weeks, why, that would be different."

I can't help but wonder if these kind of accusations are not an example of the classic propaganda technique of distraction: If you can't rebut your opponent's argument, sidetrack the debate into dispute over details. The important point here is that unborn babies are not "globs of tissue". Very early in pregnancy the developing baby is quite recognizable as a baby. The body functions that we routinely use as indicators of life in born people -- like heartbeat and brainwaves -- are present. While of course we try to quote accurate and reliable numbers, whether any particular development comes at 3 weeks or 4 or 5 or 10 makes virtually no difference to this basic argument. Is it morally acceptable to deliberately kill a baby who has a beating heart and is capable of seeing and hearing and moving his arms and legs? If your answer to that question is sure, why not, who cares, then what is the point of debating when this happens?

When I say something like the preceding couple of paragraphs in a debate, my opponent will sometimes make some sarcastic remark to the effect of, "Oh, so you don't care if your facts are right or wrong, huh?" To which I reply, No, that's not what I said. The facts that we quote on this web site are the most accurate information we have available. In some cases there are discrepancies. Let's discuss where they come from.

The Factual Issue

Can we explain such discrepancies? Yes. There are several perfectly valid reasons for them.

  1. Babies in the womb do not develop according to a single, fixed schedule. Just as some people are taller than others or have bigger noses, so some babies grow and develop faster than others. Some sources will give an average age at which a certain development happens. Others will say this development happens "by 16 weeks" (or whatever the number), by which they mean that some suitably large percentage of babies will have reached it by that time, which implies that most will have reached it sooner. And because no study includes every baby who has ever been conceived, we would expect to see minor differences just from normal, random variation.

    I have an almanac on my bookshelf that includes a table with various information about different animal species. One column of this table is labeled "Longevity". It has entries such as: "Baboon ... 20 years", "Fox (red) ... 7 years", "Hippopotamus ... 41 years", and so on. Does this mean that every fox dies exactly on his 7th birthday? Surely not. We understand such numbers to be the average or typical longevity for these animals. If I had a pet fox that lived to be 9 years old, would I be justified in concluding that the statistics in this almanac are mistakes or lies?

  2. There are a lot of things that medical researchers today do not fully understand about fetal development. Thus, different researchers sometimes reach different conclusions because they have structured their experiments in different ways.

    To take an example that the letter-writer used: How does a medical researcher know when an unborn baby is capable of hearing? Some researchers examine the bodies of miscarried babies and study the ears to see at what point they are sufficiently developed. Others study the bodies of aborted babies. Yet others study living babies in the womb. All could come to different conclusions. (For example, miscarried babies might show less development than living or aborted babies, because miscarried babies often do not develop properly -- that's a major reason for miscarriage.) Other researchers point out that examining the physical development of the ear is inconclusive because we don't necessarily know exactly what is necessary for it to function. They prefer more direct experiments, like making loud noises near a pregnant woman and watching for reactions on the part of the baby. Of course the first researcher could reply that this is equally inconclusive, because the baby may hear a sound but show no obvious reaction, or may react to vibration rather than sound, or may react to the fact that his mother reacted to the sound. Et cetera.

    If using such different methods, one researcher concludes that the unborn baby can hear at 18 weeks while another says 20 weeks, it is fair to say that these numbers are within the range of error and uncertainty we would expect from such experiments. (Of course if one says 2 weeks and another says 34 weeks, we would have to conclude that something more serious is wrong.)

  3. Different researchers use different definitions or criteria. Remember that the arrival of each function or capability in the developing baby is not something that happens instantly -- there is not one moment when the baby's heart is not beating and then the next moment it is beating at a regular pace. Rather there are flutterings and half-starts and then it gets going. In theory we might look for the "first beat", like after the baby is born we look for the first step. But in practice this sort of thing is very difficult to determine.

    And that's a simple, measurable function. Other functions can be even more difficult to pin down. When does the baby begin to hear, or to see, or to think? We cannot determine these things by a simple, direct observation. We must make interpretations based on indirect evidence. Even if the baby could speak English and tell us exactly what he is experiencing, we would have to make judgement calls about what "qualifies". Do we say that the baby can see when he has his first sensation of light? Or do we not say that he can see until he is able to distinguish shapes and colors?

  4. A technical point: We sometimes measure the age of the developing baby from conception, and sometimes from "LMP", or "last menstrual period". Clearly, counting a baby's age from conception is much more meaningful and realistic. But in practice it is often difficult to know the exact date on which a baby was conceived, while a woman usually can easily say when she had her last menstrual period. Thus some discrepancies are simply because the numbers cited are using different "yardsticks".

Thus, to take the example cited at the beginning of this article: The letter-writer is claiming that some source which he apparently considers authoritative says that the heart begins to beat at 3 weeks, which after some intensive calculation I find to equal 21 days. We quoted number of 18 days and 25 days. Given all the difficulties in determining such a thing and the normal variation between people, I would not think a discrepancy of 3 or 4 days either way to be a source of concern.

The other discrepancy he cited concerned hearing. We quoted one source that said the unborn baby can hear at 12 weeks, another that said the unborn baby can "hear and remember" at 20 weeks. Of course those two are not the same thing: I would not expect the ability to remember what he has heard to come at the same time as the general ability to recognize the presence of sound. So I see nothing disturbing in that discrepancy: these were quite different experiments. The writer cites a source that says the unborn can hear at 16 weeks. This leaves us with a discrepancy between 12 and 16 weeks. This is rather large for me to simply accept as normal uncertainty, but without fully investigating the experimental methods and definitions behind each number, I would be quite hesitant to say that one number is flatly wrong.


If we were really trying to fool people, there would be nothing easier than for us to go through all the articles we have on fetal development and change them so that all the numbers quoted are exactly the same. But we didn't do that and we're not going to, because that would be dishonest -- that is not what our original sources said. Instead, I have laboriously explained why there are inconsistencies.

But before we get embroiled in a debate over a detail, let's first ask: Does it matter? If not, then why do you bring it up? Who is it who is really trying to fool or mislead the audience here?

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Posted 9 Sep 2000.

Copyright 1999 by Jay Johansen.
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