Human Anatomy, Physiology, and Medicine. Anything human!
What you say is very interesting, KIM, and such work is very worthwhile, as it can lead to the couple achieving success eventually.
However, a laboratory such as the one you worked in would only have been sent those fetuses the clinician thought may have a genetic abnormality, based either on gross morphology/pathology, or, (as you rightly mention), the woman's obstetric history, in which 3 or more pregnancies ended this way at a particular stage of gestation.
Therefore, although 99.9% of the fetuses you examined could well have had a major genetic flaw, that would not necessarily mean that this would be the figure and cause underlying all miscarriages.
A lot depends on the point of gestation reached, but many causes abound, ranging from viruses, rhesus incompatibility, (yes, even today!), trauma, foreign body, placental insufficiency, cervical incompetence, to name but a few.
As atypical10 has already pointed out, a miscarriage is a pregnancy that ends before 20 weeks. Expanding from that, a miscarriage can also be referred to as spontaneous abortion.
There are different categories of miscarriages: early which is before 8 weeks of gestation and late which occurs between 12 and 20. There are also different types of miscarriages including threatened, inevitable, incomplete, complete and missed.
The causes for early miscarriage can vary from endocrine imblances, infections, systemic disorders or genetic factors. Some causes for late miscarriage can be the age of the mother, infection, premature dilation of the cervix, poor nutrition, and drug use. However, there are some miscarriages that happen for unknown reasons.
I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit nature and more time tasting her sweetness and respecting her seniority. ~ E. B. White
Here is quote from my mol. genetics text. Maybe it is relevant?
I think you are right, in that the term 'spontaneous abortion' means something quite distinct, so these types of miscarriage would have a very high genetic loading as a cause.
I don't think we can use this term, i.e. spontaneous abortion), as synonymous with miscarriage per se, though, and it is within this classification that the genetic causes may not be quite so high. (At least in our present stage of knowledge, perhaps).
Does the book definitely say that 90% of all chromosomal anomalies are terminated prior to birth as result of spontaneous abortion?
I am just curious. Do they mean major anomalies, or are they perhaps including therapeutic abortions in the figure? It seems a strange way to put it, if not, i.e. 'prior to birth..'.
Also, if the authors of the book state that only 30% of all spontaneously aborted fetuses demonstrate some form of chromosomal anomaly, I don't understand how the figure jumps to 90% of all fetuses undergoing spontaneous abortion prior to birth.
There is quite a lot of such pregnancies that do, sadly, end by means of a therapeutic abortion, so I do not think that 90% of all chromosomal anomalies can end purely in spontaneous abortion.
Then, there are the babies born with chromosomal anomalies. It depends on what is meant by this term, but many conditions have a chromosomal 'anomaly' at their root.
Maybe I am missing something, but, at first sight, these figures seem wrong to me.
Yes, as far as miscarriages vs spontaneous abortions, I am not sure. Maybe definition subjective?
Abortions listed are not by choice of parent of physician is that is what therapeutic abortion mean. Just spontaneous.
For percentages, I do not see conflict that you say. It says 30% of original 15%-20% demonstrate chromosome anomaly. So now we have percentage of 6% assuming original is 20%. So now we can say 6% of spontaneous abortion due to chromosomal anomaly.
For 90% is taken as different ratio. This ratio out of all babies that have chomosomal anomalies and are spontaneous aborted. If 100 babies are conceived with chomosome anomaly, only 10 will survive is way to look at it.
And chomosome anomaly refer to any deletion, inversion, aneuploidy, duplication, translocation, fragile site, etc..
Anyway, hope explanation helps.
It could well be that I am missing something, because figures are not my strong point!
I think that there is a medical definition of spontaneous abortion, and of miscarriage, (there is certainly a legal one), but I would have to check my textbooks. I don't think these definitions are subjective.
I could also be wrong about this, but I do not think that, out of every 100 fetuses conceived with a chromosomal anomaly, only 10 will survive, (by virtue of nature's input alone). This may be true of very serious anomalies that are largely incompatible with life, but not of all of them.
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