X-rays, ultrasound, CT, MRI and other imaging tests have become an indispensable part of clinical medicine. Many women who are unintentionally pregnant and think they are not aware of it because of irregular menstruation happen to undergo X-ray imaging, such as fluoroscopy or chest X-ray, and then find out that they are pregnant and worry about whether it will affect the fetus and whether it is necessary to terminate the pregnancy. What are the risks of X-rays to the fetus?
X-rays.
Chest X-ray is a small case, but CT is a very big dose.
1. Miscarriage
Within 33 days of gestation is the “all or nothing” response period for external risk factors affecting the embryo or fetus: during this time, the embryo may receive too many X-rays and miscarriage may occur, but this type of very early miscarriage may not have obvious manifestations, also known as “biochemical pregnancy”, women If a woman is careful, a urine test will reveal a positive HCG (chorionic gonadotropin); if there is no miscarriage, there is no significant increase in the risk of other fetal problems.
2. Teratogenic
After 33 days of gestation to the end of the third month is the teratogenic sensitive period, during which a large number of organs of the fetus concentrate on development, but there are also some organs for which the teratogenic sensitive period lasts until late pregnancy. Studies in Japan have found that pregnant women exposed to radiation after the atomic bombings in Hiroshima and Nagasaki are more likely to give birth to babies with microcephaly, mental retardation, or other systemic delays. Fetuses between 4 and 12 weeks of gestation are most susceptible to malformations caused by ionizing radiation. Theoretically, a radiation dose of 5-15 rad to a pregnant woman could produce fetal malformations. The radiation doses for common X-ray examinations are
A single X-ray chest X-ray is 0.00007rad, and it takes 71429 shots to exceed the minimum standard of 5rad.
The radiation dose of X-ray chest X-ray is about 5-10 times of chest X-ray, and it takes more than 7000 times to exceed the standard by the most 10 times.
Dental X-ray examination is 0.0001 rad for a single time, and it takes 50,000 times to exceed the standard.
Barium enema X-ray is 3.986 rad, and it takes two times to exceed the limit.
Single abdominal CT is 2.6 rad, and it takes two times to exceed the limit.
3. Carcinogenic
X-rays can increase the risk of malignant tumors (such as childhood leukemia) in fetuses after birth. According to a study by the University of Oxford, the risk of developing malignant tumors in early, mid and late pregnancy is 3.19, 1.29 and 1.30 times higher when compared to those who are not exposed to radiation. Note that this is a “relative risk” and the incidence of malignancy is usually very low, e.g., 1 in 100,000, so a 3-fold relative risk is only an increased incidence of 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
Pregnant women want their doctors to answer the question, “Can I do it?” or “Do I want to have a baby? However, doctors can only assess the risks and cannot give a definitive diagnosis because the risks are theoretical calculations and for the individual there are only two possibilities: yes or no.
There is a “background risk” even if the pregnant woman has not taken medication, received radiation, or other risk factors. For example, the overall risk of spontaneous abortion, fetal malformations, fetal growth abnormalities, and malignant tumors in children in the general population is 286 per 1,000, and most of these are very early spontaneous abortions, often manifested as “delayed menstruation” or “irregular menstruation” The majority of these are very early spontaneous abortions, often manifested as “delayed menstruation” or “irregular menstruation”, and 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 sum of the additional risk from radiation plus the “background risk”. Therefore, it is necessary to analyze the issue objectively and not to generalize the cause of fetal problems to radiation exposure.
2. X-rays are not as scary as the average person thinks. Some studies have shown that after exposure to 0.5 rad, the chance of adverse effects only increases by 0.17 parts per thousand from the original risk, which means that only about 1 in 6,000 fetuses receiving that dose of X-ray radiation will have an adverse outcome as a result.
3. The question of whether to terminate the pregnancy. If the fetus receives a radiation dose that is grossly excessive, the doctor may recommend termination of the pregnancy, but this is very rare. The relevant guidelines of the American Congress of Obstetrics and Gynecology say that X-ray exposure during pregnancy is not an indication for therapeutic abortion. In other words, doctors will not recommend a therapeutic abortion or induction of labor because a pregnant woman has had an X-ray.
Ultrasound and MRI: No risk of ionizing radiation
Ultrasound is a common test done in obstetrics. According to Deng Minduan, a large number of studies have confirmed that ultrasound examinations during pregnancy are safe and do not cause adverse effects on the fetus. Prolonged, high-dose, high-frequency ultrasound irradiation can cause the phenomenon of cavitation of the pregnancy sac, but this is generally only seen in animal model experiments, and this is not the case with ultrasound examinations used in the clinic, so there is no need to worry.
MRI (magnetic resonance imaging), like ultrasound, is not a radioactive test and does not produce ionizing radiation. A few animal fetal studies have found that exposure to the magnetic field of MRI in early pregnancy may be teratogenic, but some animal studies have not found effects, and there is no information on human studies.
The 1991 edition of the British “Radiation Protection Guidelines” considers MRI to be inappropriate in early pregnancy, but the 2007 edition of the U.S. “Radiation Safety Guidelines” considers MRI to be acceptable at any stage of pregnancy, as long as the patient is comfortable with the risks and benefits of MRI, and the U.S. The most recent FDA guidelines require that MRI instruments be labeled as “no safety assessment has been established” for fetal examinations. In clinical practice, the majority of MRI exams are performed in pregnant women who have other medical conditions that require further investigation and treatment, and whose diagnosis is not confirmed by conventional tests such as ultrasound. MRI is generally considered to be relatively safe in late pregnancy, and can be chosen according to the needs of the patient after evaluating the advantages and disadvantages.