Hello, and I hope I can help you today. It takes a very high dose of radiation in order to cause any harm to pregnancy. In the early first trimester, high doses of radiation will produce miscarriage, rather than a genetically abnormal fetus. Furthermore, a cumulative radiation dose of under 5 rd (which is the radiation in about three CAT scans) has not been shown to be a risk for malformations in developing human fetuses. Amniocentesis, or chorionic villus sampling, can only detect diseases of the chromosomes of the fetus. The fetuses chromosomes are formed at conception, and would not be affected by radiation exposure. Therefore these tests are not necessary unless a high risk is detected on the routine screening tests such as the triple test use in all pregnancies to calculate risk for chromosomal abnormalities. So in summary, I would not recommend aborting this pregnancy based on a radiation exposure under 5 rd before fetus even develops. I agree with your doctor to do the routine genetic screening-which consists of a triple test with nuchal translucency (NT) beginning at 11 weeks gestation and only consider amniocentesis or CVS if that testing appears normal. A level II ultrasound also is essential in every pregnancy to rule out birth defects. However, I want to reemphasize that if the fetus survives the first trimester, It is unlikely that the radiation exposure caused any effect on the pregnancy at all. I hope that I was adequately able to answer your question today, and that my advice is reassuring. Best wishes for the rest of the pregnancy, Dr. Brown