Dear Colleagues,
I am replying to the current postings concerning hCG testing to exclude
pregnancy.
I would propose a slightly different view on the topic. If we ask the
question "why are we trying to detect very early pregnancies?" The obvious
answer is to avoid damage to the conceptus. What kind of damage are we
trying to avoid? We are obviously very keen to avoid any possible
teratogenic effects of therapeutic of diagnostic interventions (drugs and
X-rays). I place this first at least partly because of the huge
medico-legal implications of errors at this stage of life. We should also
be trying to avoid early foetal loss, but at the very early stages of
pregnancy it is very difficult to separate foetal loss due to an
intervention from the very high rate of natural foetal loss.
As far as I can see from the literature as well as discussions with
colleagues in this area the chance of malformations due to any intervention
in the first 2 weeks is very, very low. We know that we can remove whole
cells without affecting the outcome of the foetus and at this stage we have
completely undifferentiated cells. Organogenesis does not commence until
about 20 days after conception at which stage nearly all pregnancy tests
will become positive. The possible outcome of an intervention may be an
increase in foetal loss which, as I said above, is difficult to distinguish
from normal events.
I make these comments not to be cavalier about very early human life, but
just to say that going to great lengths to exclude very early pregnancy
before certain interventions may not produce any appreciable changes in
outcome.
I will add a couple of the quotes I came across in searching around this
topic a few years ago. Of course I welcome any other thoughts on this topic.
General: "During the predifferentiation period in early gestation, the
conceptus is generally resistant to production of congenital malformations,
although embryonic death or abortion may occur."
Schardein, J. Chemically induced Birth defects (2nd Ed) P5. Marcel Dekker
Inc New York. 1993.
Substance must be administered during organogenesis to induce a teratogenic
effect. In humans this is between 20 and 55 days after conception (35-70
days after LMP).
Schardein, P5&6.
Radiation: "250 Rads given before 2 or 3 weeks gestation increased
spontaneous abortion, but did lead to severe congenital anomalies."
Burrow and Ferris. Medical complications during pregnancy. P546. WB
Saunders Company 1988.
Regards,
Graham
Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
Victoria St, Darlinghurst, 2010
NSW, Australia
Ph: (02) 8382-2170 Fax (02) 8382-2489
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