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Having been to three ultrasounds for my children, I'm amazed how casually they use a 2D length to estimate the baby's age, and therefore delivery date, and ther

Having been to three ultrasounds for my children, I'm amazed how casually they use a 2D length to estimate the baby's age, and therefore delivery date, and therefore when it is overdue and calls for a cesarean, etc. Your results seem like they confirm my suspicions that this can't possibly be very accurate.

Stefan-H 12y ago
With babies we know the shape. It is not as if we are likely to get a 2d slice of just an arm to estimate the age. With tumors we do not have an idea of the shape, and therefore could accidentally take a slice of the narrowest portion the first time, then the largest portion the second and assume it grew.
snowwrestler 12y ago
The real problem here is the concept of "overdue" tied to interventions. Babies are like wizards: they are never late. They arrive promptly when they intend to. And there is actually not much evidence that arriving within a week or two on either side of the "due date" has any correlation with health problems for the mother or baby. So, a well-educated OB can be a bit casual about the exact age of the fetus because it doesn't really matter all that much.
Florin_Andrei 12y ago
Or maybe you're seeing just a slice of a procedure with a more complex theory behind it that you're not aware of. Remember, being good at computers does not imply being good at medicine. This should be self-evident, but just a quick perusal of some comments here shows the contrary.
- pjungwir 12y ago
  Yes, I completely agree. It's not like I'd take action on my doubts. I'm sorry if my original comment sounded critical---that wasn't my point. But it is crude, isn't it? I believe even doctors concede that these estimates are not very accurate (especially when taken mid/late in the pregnancy), and it is sort of alarming to watch a nurse snap lines across the skull cross-section freehand and use those. I find that in general with medicine my intuition battles against what my intellect knows must be the case. It's not like anything in the body is far away. Cancer isn't even very small. Isn't it weird that it's so hard to treat? Obviously it must be, but it feels like it should be easy. The patient is a foot away. We are inscrutably powerless. When every day you command computers and they obey, when you can summon distant people and their image appears before you, when you can instantly consult more lore than in the greatest library, when you see people casually toting radiant tablets of spellbinding powers, progress in medicine feels so slow, so analog---so carnal. I know it's wrong, and we live in a world of medical miracles, with vaccines and antibiotics and DNA and everything else, but sometimes I can't help but feel that nothing has happened since Galen. It's not an argument, it's a feeling, but one with pathos that I'm sure many share.
gdh73 12y ago
I was wondering the same since the Crown–rump length (CRL) measurement only has two points. One would think the spine should be included for an accurate measurement. However, that must be accounted for already. See also, "3. First-trimester fetal measurements" and "4. Assessment of gestational age" here: http://onlinelibrary.wiley.com/doi/10.1002/uog.12342/full http://onlinelibrary.wiley.com/doi/10.1002/uog.12342/full

Stefan-H 12y ago

With babies we know the shape. It is not as if we are likely to get a 2d slice of just an arm to estimate the age. With tumors we do not have an idea of the shape, and therefore could accidentally take a slice of the narrowest portion the first time, then the largest portion the second and assume it grew.

snowwrestler 12y ago

The real problem here is the concept of "overdue" tied to interventions. Babies are like wizards: they are never late. They arrive promptly when they intend to. And there is actually not much evidence that arriving within a week or two on either side of the "due date" has any correlation with health problems for the mother or baby. So, a well-educated OB can be a bit casual about the exact age of the fetus because it doesn't really matter all that much.

Florin_Andrei 12y ago

Or maybe you're seeing just a slice of a procedure with a more complex theory behind it that you're not aware of. Remember, being good at computers does not imply being good at medicine. This should be self-evident, but just a quick perusal of some comments here shows the contrary.

pjungwir 12y ago
Yes, I completely agree. It's not like I'd take action on my doubts. I'm sorry if my original comment sounded critical---that wasn't my point. But it is crude, isn't it? I believe even doctors concede that these estimates are not very accurate (especially when taken mid/late in the pregnancy), and it is sort of alarming to watch a nurse snap lines across the skull cross-section freehand and use those. I find that in general with medicine my intuition battles against what my intellect knows must be the case. It's not like anything in the body is far away. Cancer isn't even very small. Isn't it weird that it's so hard to treat? Obviously it must be, but it feels like it should be easy. The patient is a foot away. We are inscrutably powerless. When every day you command computers and they obey, when you can summon distant people and their image appears before you, when you can instantly consult more lore than in the greatest library, when you see people casually toting radiant tablets of spellbinding powers, progress in medicine feels so slow, so analog---so carnal. I know it's wrong, and we live in a world of medical miracles, with vaccines and antibiotics and DNA and everything else, but sometimes I can't help but feel that nothing has happened since Galen. It's not an argument, it's a feeling, but one with pathos that I'm sure many share.

gdh73 12y ago

I was wondering the same since the Crown–rump length (CRL) measurement only has two points. One would think the spine should be included for an accurate measurement. However, that must be accounted for already. See also, "3. First-trimester fetal measurements" and "4. Assessment of gestational age" here: http://onlinelibrary.wiley.com/doi/10.1002/uog.12342/full http://onlinelibrary.wiley.com/doi/10.1002/uog.12342/full