How much influence does ct and X-ray for pregnant women have on the growth and development of children's bodies?

Common misunderstandings and guidelines for imaging examination during pregnancy. At present, there are often the following misunderstandings in clinic: ① Radiological examination such as X-ray during pregnancy will greatly increase the risk of miscarriage and fetal malformation, and pregnancy should be terminated; ② Never do positron emission tomography (PET)/CT examination during pregnancy, otherwise it will lead to fetal defects.

The American College of Obstetrics and Gynecology (ACOG) issued the guidelines for imaging examination during pregnancy on 20 16. The suggestions are as follows:

① Ultrasound and magnetic resonance imaging (MRI) have no risk of ionizing radiation and are relatively safe examinations during pregnancy, but they are only recommended for related clinical problems or when they bring medical benefits to patients;

② Except for a few cases, the radiation exposure dose caused by X-ray examination, CT scanning and PET/CT is far lower than that caused by fetal damage. If these examinations are necessary supplements to ultrasound or MRI, or are more conducive to disease diagnosis, they should not be rejected.

③ Only when the clinical benefits outweigh the risks, it is recommended that pregnant women use gadolinium as MRI contrast agent (that is, MRI enhancement examination).

Risk analysis of imaging examination during pregnancy The risk of imaging examination during pregnancy to fetus is related to gestational age and ionizing radiation dose (table 1). Higher doses of radiation can lead to birth defects, growth restriction and mental retardation of the fetus, among which 8~ 15 weeks of pregnancy has the greatest impact on the central nervous system. In addition, the fetus will be exposed to certain natural background radiation during pregnancy, and its dose is about 1 mGy. High dose ionizing radiation (> > 1 Gy) in early pregnancy may lead to the risk of embryo death.

X-ray examination When the radiation exposure dose of the fetus is less than 50 mGy, no research shows the risk of growth restriction, fetal malformation and abortion, and the fetal dose range of most diagnostic X-ray examinations is far below 50 mGy (Table 2). In addition, it is not clear whether intrauterine ionizing radiation is carcinogenic, but it is unlikely.

Therefore, intentionally or unintentionally taking X-rays during pregnancy, there is no need to terminate pregnancy. However, if X-ray examination is carried out many times, it is necessary to consult with radiologists and obstetricians to calculate the total radiation dose of the fetus and evaluate the possible impact on the fetus.

CT plain scan and CT enhanced scan CT uses X-ray beams to scan a certain thickness of the inspection site from multiple directions. Similar to X-ray examination, the risk of CT examination is related to gestational age and radiation dose, and the radiation dose to the fetus depends on the scanning location, scanning layers and layer spacing. If pregnant women undergo head CT examination, the radiation dose to the fetus is only1.0 ~10mgy; However, if pelvic CT examination is performed, the radiation exposure dose of the fetus can be as high as 50 mGy. Therefore, if pelvic CT examination is necessary, we should fully communicate with radiologists and technicians to minimize the radiation dose without affecting the examination effect.

Enhanced CT examination is often used for further diagnosis, and the commonly used contrast agent is meglumine diatrizoate (ionic monomer iodine). Meglumine diatrizoate can enter fetal tissue through placenta. If the abdomen is exposed to X-rays many times during radiography, it may have adverse effects on the fetus. However, in previous animal and human experiments, there is no clear evidence to show the specific damage of iodine contrast to the fetus. Therefore, if there are clear indications in clinic, we should not refuse to use CT plain scan plus enhanced examination, but should fully weigh the advantages and disadvantages and use it carefully.

There is no risk of ionizing radiation in MRI plain scan and enhanced scan, and the safety of MRI plain scan is relatively certain. Gadolinium is a commonly used contrast agent in MRI enhancement examination, and the risk of its use during pregnancy is still controversial. Gadolinium is water-soluble and can enter fetal circulation and amniotic fluid through placenta. Free gadolinium is toxic. Although its chelates have been used in clinic, large and repeated doses of gadolinium still have teratogenic effects, and should only be considered if the advantages outweigh the disadvantages.

The radiation dose of PET/CTPET/CT depends on the physical and biochemical characteristics of radioisotopes. Usually, the fetal radiation exposure dose of PET/CT examination is 10~50 mGy.

But not all radioisotopes are safe to use during pregnancy. For example, I- 13 1 easily crosses the placenta, causing adverse effects on fetal thyroid, with a half-life of 8 days. Therefore, I- 13 1 should not be used for diagnostic or therapeutic purposes during pregnancy.

Because PET/CT has unique advantages in the diagnosis of tumor characterization and recurrence, if pregnant women have clinical indications after full evaluation, they should inform patients and their families of their illness, "choose the lesser of the two evils", choose isotopes that are less harmful to the fetus for PET/CT examination, and use them in small doses as far as possible without affecting the examination effect.