<prompt> Fetus is most radio sensitive at which week?3 weeks8 weeks12 weeks15 weeks  <response>: ANSWER: A 3 weeksREF: Primer of radiobiology by Elizabeth Latorre Travis page 196The first trimester, particularly the first 6 weeks of development, appears to be the most radiosensitive in terms of both lethality and induction of congenital abnormalities in humansHence the answer is 3 weeks 