How on earth did it become common practice to measure the actual femur length against the 50th percentile femur length for gestational age for fetuses?

I mean, when you see someone on the street and you think they have short legs (or long), are you comparing them to a hypothetical half-man/half-woman 5' 7 1/2" person with absolutely normal legs? Which is what this is, in practice, since girl fetuses are smaller than boy fetuses.

The other standard seems to be to compare the length of the femur to the width of the head. Which at least has the virtue of looking at an internal ratio of the actual body involved, but still.

Again, when you see someone and you think they have short legs is it because the legs look short in relation to their head?

Doesn't everyone, when they notice or think about it at all, look at the length of the legs in comparison to the rest of the body?

Not only do these practices catch small fetuses with legs verging on "short", but they are sure to miss large fetuses with actually short legs, because they're not comparing the legs to the rest of that baby's actual body. They're comparing it to a mathematically normal body. A mathematically normal body that probably does not exist much of the time. My BIL told me that his grandson was diagnosed with a head size in the 0th percentile. Can you imagine how that would panic you, if you were the parent getting that ultrasound diagnosis? I mean what, your son doesn't have a head? No, it's just a very small, otherwise completely normal head. Apparently he's now 4 years old, quite bright, and can still wear newborn sized caps.

How much of what I've just been put through is rank stupidity, in both the standard practices and in the individuals involved?

Stupidity of Persons Involved: Who did not know, or act as if they knew, that the cut-off for dwarfism concerns is 2 standard deviations from the mean, or 2.4 percentile. Baby is at 5. Who did not initially look at any other indications of dwarfism, like mineralization of the bones, shape of the bones, size of the thorax (chest) or spine, etc. Who did not relate the risk information when communicating this to me, and did not say that "your baby has legs in the 5th percentile, and dwarfism is at most 1/5000, so the chances are still very small; besides all the other signs are still absent." Who did not compare the 28 week ultrasound to the 20 or 22 week ultrasounds, in which they would have seen that the actual/expected ratio for the femur has actually remained fairly constant at 87-92% throughout.

I'm not an expert, I didn't go to medical school, I'm not making $200g/year. Yet I can see that this makes no sense.

And, well, we've already seen the stupidity of the actual practices, which identifies 2.5% of all babies at risk for a condition that strikes 1/5000. That's just bloody arithmetic. You don't even need to have gone to highschool to see that doesn't work.

And now with the DS thing.

Well, you know me. I did my research.

Yes, short femurs are a screening tool for DS. "Short" here is defined as 90% of expected length or less. So for DS, yep, we're short. What does a "screening tool" mean?

It means that all or nearly all infants with DS will be so identified. It does NOT mean that all infants so identified have DS, or even most of them, or even a significant portion of them. Statistically, it means that having a short femur may (in combination with other screening measures, like maternal age, presence of other markers, blood test results, etc.) raise your own risk of a DS baby to a level where the chance of finding out that your baby has it is greater than the risk of miscarriage implicit in any of the methods to find out. In other words, your risk is elevated to >1/270. Or, in 270 such pregnancies, one baby will have DS.

Based on the literature I've managed to find and review--none of it offered by the doctors, oh no, of course not--it looks like baby's fetal biometry has changed my baseline risk from about 1/1000 (based on age alone) to about 1/250 to 1/500. So I may be just barely considered "high risk" as defined by 1/270.

Which means that the chances of losing a healthy pregnancy by getting the tests done are the same as the chance of having a baby with DS, for me right now.

Well, that's just peachy.

If you'd think that would make me feel better, you'd be wrong. Oh, it's true that I feel much better now than I did after the 30 week appointment, when I basically went through each day in a semi-comatose state and went home every night and cried. (This is why doctors should not treat patients as stupid people and should tell them all the relevant information.) But even a shadow of a possibility that there might be something wrong is just too much. In terms of anxiety and stress, anyway.

I found a really interesting journal article on the UofT library site, which discusses the utility of ultrasound in screening for DS and the impact of such diagnoses (both true and false) on the woman, the couple, and the pregnancy.

1. "False Positive" in ultrasound diagnosis means that a pregnancy is labelled as "high risk" for one of these disorders, and is subsequently found to be normal. It doesn't mean that they told you it is a problem, only that it could be. So now, potentially, I've had two.

2. Data on the "soft markers" for various conditions (a "hard marker" means "yup, you've got it"; a "soft marker" increases the statistical risk by varying amounts but has little significance in itself. Femur length is a "soft marker") is generally collected from high-risk populations. For DS, that means that studies generally look at women over 35 or who have had "positives" on previous blood screening tests. After the research I've done, I can confirm this. The number of studies of diagnosing DS by ultrasound, or even screening for it, that use women considered "low risk" is, well, low. A handful. Maybe. But the results of the studies on high-risk pregnancies are applied to all pregnancies, low-risk included.

3. The use of soft-markers in ultrasound screening led, in one general population study, to a 4% increase in true diagnoses, vs. a 12-fold increase in false positives.

4. In Great Britain, 2% of all pregnant women receive a "high risk" designation on the basis of soft markers in ultrasound screening (apart from high-risk labels already dished out by age, health, smoking, etc.). So 2% end up being told they are high risk for something that happens to only 1/750 live births.

5. In the US, that number is 5-10% of previously low-risk women because of the litigative atmosphere and wrongful birth suits (I'm not making that up).

My guess is that Canada is somewhere in the middle, though it's not indicated in the article.

6. Due to the poor diagnostic ability of soft markers, some studies have shown that up to 4 healthy fetuses will be lost through amniocentesis or other invasive diagnostic procedures for every one case of DS that is diagnosed as a result of them.

7. The sensitivity of the tests are generally considered to be 75-80%. That means 75-80% of fetuses with DS will be referred for further testing, and 20-25% of fetuses with DS will be missed altogether. The false positive rate is 5%. This sounds reasonable, until you see that (as the authors calculate it) "Among the 4000 pregnancies monitored during that year, 5-6 children with Down syndrome would expectedly have been born in the absence of prenatal testing. For each child to be diagnosed, it can be calculated that 30-40 expectant couples received information about an increased risk for Down syndrome and underwent invasive diagnostic testing." (4,000 pregnancies = 4,000 ultrasounds; 4,000 ultrasounds at 5% false-positive rate gives 200 false positives; 200/5.5 actual cases=35 or 30-40 couples.)

In every article I read, this was considered an "acceptable" level of accuracy for prenatal screening for DS. But it doesn't look so good when you actually calculate it out, does it?

8. Now consider the effects of those false positives on the couple: There is only one study that looked at the psychological and emotional impact of a false-positive diagnosis from ultrasound on a couple, and it was not a good thing: "...the identification of fetal soft markers can be profoundly distressing .... Many interviewees perceived that the disclosure of a soft marker left them with almost impossible choices and had created a state of alienation and crisis which most felt compelled to resolve.... The presence of soft markers made a majority of women put their pregnancy 'on hold' whilst waiting for results of invasing testing; one woman described how she literally closed the door to the baby's room." Can I say hell yes, please. For a solid week I couldn't even look at the closed door. Goes on to say: "...Baillie noted how attempts to establish emotional distance from the fetus was often accompanied by feelings of confusion, alienation and ambivalence."

She goes on to talk about how the distress and anxiety continues even after invasive testing rules out the problem, and can be severe. It can continue not only throughout the pregnancy but afterwards, leading to a parental perception of fragility in their children throughout their lives.

9. And what is the effect of all this on the fetus?

They are affected by maternal emotions, including anxiety. Maternal anxiety and distress during pregnancy can cause problems in the unborn child and has been linked to behavioural problems in the child after birth.

I can tell you for sure that this little Sprout responds to anxiety. On the day of the diagnosis and throughout that weekend, she was bopping and thrashing away like a wild thing. I don't know what all that maternal cortisol and adrenaline does to a baby in the long term, but it can't be positive. Even now, this afternoon, while I was writing this she was more active than usual.

My experience of this pregnancy has been permanently altered. Even though mentally I can recognize that the risk is low, the anxiety and tension of not knowing and hearing that there might be something wrong is a constant now. It wasn't worth it. If I had any choice but this high-risk clinic and their "standard of care" that made all of this mandatory for me, I would take it. I would give birth in the Ganges river if that was the only other option I had.