The effects of X-rays on the embryo or fetus are as follows: 1. Miscarriage Within 33 days of gestation (counting from the start of the last menstrual period of the pregnant woman) is the period of reaction to external risk factors affecting the embryo or fetus: during this period, the embryo can suffer a miscarriage if it receives excessive X-rays, but this kind of very early miscarriage may not have obvious manifestations, which is also known as “biochemical pregnancy”, the woman may just feel that her menstruation has been delayed for a few days. However, this kind of very early miscarriage may not have obvious manifestations, also known as “biochemical pregnancy”, women may just feel that their menstruation has been delayed for a few days, and careful women will find HCG (chorionic gonadotropin) positive if they take a urine test; if there is no miscarriage, the risk of the fetus developing other problems will not be increased significantly. 2, teratogenic After 33 days of gestation to the end of the third month is the sensitive period of teratogenicity, during which a large number of organs of the fetus concentrated development, but there are also some organs of teratogenicity sensitive period will continue to the end of pregnancy. Fetuses between 4 and 22 weeks of gestation are most susceptible to malformations caused by ionizing radiation. Theoretically, fetal malformations can occur when a pregnant woman receives a radiation dose of 5 to 15 rad. The radiation dose of a common X-ray examination is 0.00007 rad for a single X-ray chest radiograph, and it takes 71429 shots to exceed the minimum standard of 5 rad. X-ray chest X-ray radiation dose is about 5 to 10 times the chest film, to the most 10 times the calculation also need to take more than 7000 times to exceed the standard. A single dental X-ray is 0.0001 rad, and it takes 50,000 shots to exceed the standard. A barium enema X-ray is 3.986 rad, which is exceeded after two shots. Abdominal CT is 2.6 rad for a single time, and the standard will be exceeded if it is taken twice. X-rays can increase the risk of malignant tumors (such as childhood leukemia) in fetuses after birth. Compared with those who are not exposed to radiation, the risk of malignant tumors is 3.19 times, 1.29 times and 1.30 times higher in early, middle and late pregnancy. The incidence of malignant tumors is usually low. Regarding the risk of X-rays, pregnant women would like their doctors to answer the question, “Can I have X-rays?” or “Should I have the baby? However, doctors can only assess the risk and cannot give an absolute answer. Some studies have shown that after exposure to 0.5 rad, the chance of adverse effects only increases by 0.017% from the original risk, i.e., about 1 in every 6,000 fetuses exposed to this dose of X-rays will have an adverse outcome. Ultrasound is a commonly performed test in obstetrics. Ultrasound during pregnancy is safe and does not cause adverse effects on the fetus.MRI (Magnetic Resonance Imaging), like ultrasound, is not radioactive and does not produce ionizing radiation. In clinical practice, most of the MRI examinations are done when the pregnant women have other diseases, which need to be further identified and treated, and the routine examination such as ultrasound fails to confirm the diagnosis. At present, it is generally believed that MRI examination in late pregnancy is relatively safe, and MRI should be avoided as much as possible in the early stage of pregnancy.