Both of malformations and for damage to the brain is a threshold dose of 100 mSv. To radiation must be fatal in fetal life, is the threshold of 200 mSv in the first trimester and over 500 mSv later in pregnancy. It is dose sizes extremely rarely achieved by radiographic examination.
Radiation doses at various studies
There are studies that show made radiation dose in mSv on fetus for part studies carried out on the mother. Different ways to take pictures of and differences in equipment and techniques means that doses may vary somewhat. On average, the leading x-ray of head or x-ray of the lungs to less than 0.01 mSv. X-ray of the kidneys (urography) and x-ray study of lumbar spine average 1.7 mSv (maximum 10 mSv). Candling of the colon leads to average 6.8 mSv (max. 24 mSv).
mSv definitions: http://www.abbreviationfinder.org/acronyms/msv.html
CT study of the head causes less than 0.005 mSv and CT examination of lungs 0.06 mSv. CT of the entire stomach area (abdomen) gives the radiation dose on average 8.0 mSv (max. 49 mSv), CT of spine 2.4 mSv (max 8.6), while CT of pelvis allows the average radiation dose to the fetus at 25 mSv (max 79 mSv).
CT definitions: http://www.abbreviationfinder.org/acronyms/ct.html
Ultrasound examination or MRI examinations do not entail any x-ray radiation.
MRI definitions: https://en.wikipedia.org/wiki/MRI
Pregnant women should only be taken as a starting point, the x-rays, if it has therapeutic impact of pregnancy. It follows the general principle that pregnant for the sake of the fetus should be spared as much as possible. There are situations where x-ray photography is recommended, even if the patient is pregnant. One example is the x-ray of the lungs where there is suspicion of tuberculosis.
If there are good medical reasons to carry out x-ray examinations of pregnant or if there will be taken pictures without being known to the pregnancy, it may be helpful to read the instructions from the National Institute of radiation protection (SIS).
SIS says on the basis of international recommendations, that there will never be any reason to recommend abortion, if the radiation dose to the foetus is estimated to be less than 100 mSv. Usually there is no radiographic examination, which comes up in such radiation doses.
There can often be the concerns of parents who have been exposed to radiation of ovaries or testes before fertilization. Conclusion based on the available knowledge is that this does not result in increased risk of malformation, abnormalities in mental development or increased cancer risk in the child.