Abstract: Imaging examinations such as X-rays, B-ultrasound, CT, and MRI have become an indispensable part of clinical medicine. Many expectant mothers worry that the \”radiation\” from these examinations will cause harm to the fetus, such as teratogenesis or leukemia in the future. Large doses of ionizing radiation are scary, but even more scary is ignorance. Imaging examinations such as X-rays, B-ultrasound, CT, and MRI have become an indispensable part of clinical medicine. Many expectant parents worry that the radiation from these tests may cause harm to the fetus, such as causing teratogenesis or leukemia in the future. Some pregnant women know that they have been photographed, and in order to give birth to a healthy baby, they grit their teeth and have an abortion. Large doses of ionizing radiation are scary, but even more scary is ignorance. Guangzhou obstetrics and gynecology experts analyzed in detail the risks, pros and cons of various common imaging examinations, and pointed out that the radiation dose of X-rays is far lower than the lowest dose that can cause fetal problems. In fact, doctors generally do not directly recommend whether to terminate a pregnancy. Instead, pregnant women make their own choices with informed consent.
X-ray:
Small cases on chest X-ray, large doses on CT
Many women have unplanned pregnancies and think they are due to irregular menstruation, but do not realize it. During this period, there happened to be X-ray imaging examinations, such as X-rays or chest X-rays during the physical examination in the unit. It will affect the fetus and whether it is necessary to terminate the pregnancy. Deng Minduan, director of gynecology and pediatrics at Guangzhou Red Cross Hospital, said that the effects of X-rays on embryos or fetuses include the following aspects:
1. Abortion
Within 33 days of pregnancy (calculated from the last menstrual period of the pregnant woman) is the all-or-no reaction period when external risk factors affect the embryo or fetus: during this period, poor embryonic development and miscarriage may occur. Excessive X-ray examinations are required, but this extremely early miscarriage There may be no obvious symptoms, also known as biochemical pregnancy. Women may only feel that menstruation is delayed for a few days. Careful women will find that HCG (chorionic gonadotropin) is positive and do a urine test; if there is no miscarriage, the risk of other problems in the fetus is very low. No significant increase, i.e. usually no problem.
2. Teratogenic
The teratogenic sensitive period is from the 33rd day of pregnancy to the end of March. A large number of fetal organs develop intensively, but the teratogenic sensitive period of some organs will continue until the third trimester of pregnancy. Japanese research has found that pregnant women exposed to radiation after the atomic bombings of Hiroshima and Nagasaki were more likely to give birth to babies with microcephaly, mental retardation or other systemic developmental delays. Fetuses between 4 and 22 weeks of gestation are most susceptible to malformations caused by ionizing radiation. Theoretically, if a pregnant woman receives a radiation dose of 5-15 rad, it may cause fetal malformations. The radiation dose for common X-ray examinations is:
A single chest X-ray is 0.00007 rad, and 71,429 times are required to exceed the minimum standard of 5 rad.
The radiation dose of chest
single dental visitX-ray examination is 0.0001rad, exceeding the standard requires 50,000 times.
The single barium enema X-ray examination was 3.986rad, which exceeded the standard twice.
The abdominal CT scan was 2.6 rads in a single scan and exceeded the standard twice.
3. Carcinogenic
X-rays can increase the risk of malignant tumors such as childhood leukemia after birth. A study from the University of Oxford showed that compared with people who had not been exposed to radiation, people who were exposed to radiation in the first, second and third trimesters had a risk of malignant tumors of 3.19, 1.29 and 1.30 times respectively. Note that this is a relative risk. The incidence of malignant tumors is usually very low, such as one in 100,000. A relative risk of three times only increases the incidence to 3 in 100,000, which is actually very low.
Decision-making: Pregnant women need to make their own choices after knowing the risks of X-rays
Regarding the risks of X-rays, pregnant women really hope that doctors can answer whether they can take X-rays and whether they should give birth. In this regard, Deng Minduan said that doctors can only assess the risk and generally cannot answer whether it will happen, because the risk is a theoretical calculation, and for individuals, there are only two possibilities. Doctors can never guarantee that there will be no problems with the fetus, and the final choice rests with the patient. He reminded the following three points:
1. Even if pregnant women do not take medicine, receive radiation and other risk factors, there is still \”background risk\”. For example, the overall risk of spontaneous abortion, fetal malformation, abnormal fetal development, and malignant tumors in children in the general population is 286, and most of them are very early spontaneous abortions, which often manifest as delayed menstruation or irregular menstruation. They are seen in older women. If a pregnant woman is exposed to risk factors such as radiation, the overall risk of fetal abnormalities is equal to the additional risk from radiation plus the background risk. Therefore, this issue needs to be analyzed objectively, and the cause of fetal problems cannot be generally attributed to the radiation received.
2. X-rays are not as scary as ordinary people imagine. Studies have shown that after exposure to a dose of 0.5rad, the chance of adverse reactions will only increase by 0.17 on the basis of the original risk, that is, about 1 in every 6000 fetuses who receive this dose of X-ray radiation will be affected. There is a bad ending.
3. The question of whether to terminate the pregnancy. Doctors may recommend terminating the pregnancy if the fetus receives significantly higher doses of radiation, but this is very rare. Guidelines from the American College of Obstetricians and Gynecologists state that X-ray exposure during pregnancy is not an indication for therapeutic abortion. In other words, doctors will not recommend therapeutic abortion or induction of labor just because a pregnant woman has had an X-ray.
Ultrasound and MRI: No danger of ionizing radiation
B-ultrasound is a common obstetric examination. Deng Minduan said that a large number of studies have confirmed that B-ultrasound examination during pregnancy is safe and will not cause adverse effects on the fetus. Long-term, large-dose, high-frequency ultrasound irradiation can cause gestational sac cavities, but this usually only occursIn animal model experiments, this situation does not occur in clinical ultrasound examinations, so there is no need to worry.
Like B-ultrasound, MRI (nuclear magnetic resonance) is not a radioactive examination and does not produce ionizing radiation. A few studies on animal fetuses have found that exposure to magnetic fields from MRI examinations during early pregnancy may cause teratogenesis, but some animal experiments have not found any effects, and there is no human experimental data. The 1991 version of the British Radiation Protection Guidelines believes that MRI is not suitable for early pregnancy, but the 2007 version of the US Radiation Safety Guidelines believes that as long as the patient can accept the risks and risks of MRI, MRI can be done at any stage of pregnancy, while the US Food and Drug Administration (FDA) Latest guidance requires MRI equipment to indicate fetal testing is still
The words \”security assessment\” have not been established. Deng Minduan said that in clinical practice, most cases where MRI examinations are performed are that pregnant women have other diseases and need to further identify the condition and treatment, but conventional examinations such as B-ultrasound cannot confirm the diagnosis. Currently, it is generally believed that MRI examinations in the third trimester are relatively It is safe and can be selected according to the needs of the condition after evaluating the various pros and cons. MRI should be avoided as much as possible in the first trimester. Text/Reporter Wu Junyi Correspondent Hu Yingyi