Re: Op-Ed in International Herald Tribune

[andrew_mcewan@nrl.moh.govt.nz]

In Rob Barish's article he states

Such a decision could be of great importance

during a woman's first few weeks of pregnancy, a time when a human embryo is

particularly sensitive.



What is the basis for this statement?



ICRP Publication 84 paragraph 24 states

"The effects of exposure to radiation  on the conceptus depend on the time of exposure relative to conception and the amount of absorbed dose.  When

the number of cells in the conceptus is small and their nature is not yet specialised, the effect of damage to these cells is most likely to take the

form of failure to implant or of an undetectable death of the conceptus; malformations are unlikely or very rare.  Exposure of the embryo in the first

two weeks following conception is not likely to result in malformation or fetal death, despite the fact that the central nervous system and heart are

beginning to develop in the third week.  During the rest of the period of major organogenesis, conventionally taken to be from the third week after

conception, malformations may be caused especially in the organs under development at time of exposure.  These effects have a threshold of 100-200 mGy

or higher."



Andrew McEwan

_______________________

Andrew C McEwan PhD

National Radiation Laboratory

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Ph 64 3 366 5059

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Andrew_McEwan@nrl.moh.govt.nz