At 10:27 19/05/05 +0100, Ted Harding wrote:
>I think Age of Mother may not be so straightforward a factor as
>it might seem on the surface.
>Our experts on Obs&Gyne can help with the facts of today, but
>my memory of the situation some 20-odd years ago was that once
>a caesarean had been performed then subsequent births to the
>same mother would also be by caesaren (because of the damage
>to the uterus and risk of rupture in normal labour).
>On that basis, one would expect an increase with Age of Mother
>since subsequent births occur at later ages.
I think we discussed this point earlier in this (or 'that'!) thread. What
you say of obstetric practice was most certainly true 20+ years ago, for
the reasons you mention. Looking back at my undergraduate notes (yes, I
still have them!), 'previous Caesarian Section (CS)' was very much at the
top of the list of reasons for considering an elective CS. I couldn't
pretend to be up-to-date with current obstetric practice, but my colleagues
who are tell me that it remains close to the top of the list for
'considering' CS, but that 'consideration' does not result in a decision to
undertake elective CS as often as it used to. Improvements in CS
technique, improved monitoring during labour and epidural/spinal
anaesthesia (which permits 'emergency' CS with far less risk than in the
past) mean that women who have had a previous CS are not uncommonly allowed
to at least attempt a vaginal delivery, with emergency CS as the fallback
option.
Needless to say, the situation will also depend upon the reason for the
previous CS. Quite apart from the risks of uterine rupture, if a woman had
a previous CS because her pelvis was judged too small for a vaginal
delivery to be possible/safe, that same situation is going to persist
through subsequent pregnancies (unless they involve an unusually small foetus).
>Presentation of rates merely by Age cannot separate out sequential
>dependencies of this kind.
That's obviously true, but I'm not sure it is necessarily all that much of
a problem (unless/until one wants to look at those particular details). In
terms of the initial analyses, it seems to me that it merely offers part of
the _explanation_ for the CS/age relationship. As I've said several times,
I would not expect that relationship to be very linear, and this
'sequential dependency' seems to merely represent one of the explanations
for that non-linearity.
Another factor we have not explicitly considered is that of multiple
births. I don't know whether the incidence of multiple births has been
rising (although increasing use of IVF may well have had that effect), but
that could also be a factor in two senses - real and 'artefactual'. The
real sense is that CS is much more common for multiple births. The
'artefactual' sense is that, as far as I can make out, the CS figures we
are able to find relate to BIRTHS - in other words, I suspect that if a
woman had triplets by CS, that would count as '3 Caesarian Sections' in the
'headline' statistics we have seen.
Kind Regards,
John
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