Radiation and Pregnancy: A Fact Sheet for the Public
Note: If you are pregnant (or if you are thinking about getting pregnant) and you have questions about how radiation exposure could affect you or your pregnancy, you should talk with your doctor. Your doctor can help you better understand the risks of radiation exposure to you and to your developing baby.
The Centers for Disease Control and Prevention (CDC) has prepared this fact sheet to help you understand the possible health effects to your fetus from exposure to radiation.
Prenatal Radiation Exposure
The exposure of a fetus to radiation is referred to as prenatal radiation exposure. This can occur when the mother's abdomen is exposed to radiation from outside her body. Also, a pregnant woman who accidentally swallows or breathes in radioactive materials may absorb that substance into her bloodstream. From the mother's blood, radioactive materials may pass through the umbilical cord to the baby or concentrate in areas of the mother's body near the womb (such as the urinary bladder) and expose the fetus to radiation.
The possibility of severe health effects depends on the gestational age of the fetus at the time of exposure and the amount of radiation it is exposed to. Unborn babies are less sensitive during some stages of pregnancy than others. However, fetuses are particularly sensitive to radiation during their early development, between weeks 2 and 18 of pregnancy. The health consequences can be severe, even at radiation doses too low to make the mother sick. Such consequences can include stunted growth, deformities, abnormal brain function, or cancer that may develop sometime later in life. However, since the baby is shielded by the mother's abdomen, it is partially protected in the womb from radioactive sources outside the mother's body. Consequently, the radiation dose to the fetus is lower than the dose to the mother for most radiation exposure events.
Pregnant women should consult with their physicians if they have any concern about radiation exposure to their fetus.
Increased Cancer Risk
Radiation exposure before birth can increase a person's risk of getting cancer later in life.
Unborn babies are especially sensitive to the cancer-causing effects of radiation. However, the increased risks depend on the amount of radiation to which the baby was exposed and the amount of time that it was exposed. For example, if the radiation dose to the fetus was roughly equivalent to 500 chest x-rays at one time, the increase in lifetime cancer risk would be less than 2% (above the normal lifetime cancer risk of 40 to 50%).
Other Risks from Radiation Exposure
Health effects other than cancer from radiation exposure are not likely when the dose to the fetus is very low.
Most researchers agree that babies who receive a small dose of radiation (equal to 500 chest x-rays or less) at any time during pregnancy do not have an increased risk for birth defects. The only increased risk to these babies is a slightly higher chance of having cancer later in life (less than 2% higher than the normal expected cancer risk of 40 to 50%).
During the first 2 weeks of pregnancy, the radiation-related health effect of greatest concern is the death of the baby.
The fetus is made up of only a few cells during the first 2 weeks of pregnancy. Damage to one cell can cause the death of the embryo before the mother even knows that she is pregnant. Of the babies that survive, however, few will have birth defects related to the exposure, regardless of how much radiation they were exposed to.
Large radiation doses to the fetus during the more sensitive stages of development (between weeks 2 and 18 of pregnancy) can cause birth defects, especially to the brain.
When a fetus is exposed to large doses of radiation (above the dose received from 500 chest x-rays) during the more sensitive stages of development (especially between weeks 8 and 18 of pregnancy), the health consequences can be severe, especially to the brain. Fetuses in the 8- to 18-week stage of pregnancy exposed to the atomic bombs dropped on Hiroshima and Nagasaki were found to have a high rate of brain damage that resulted in lower IQs and even severe mental retardation. They also suffered stunted growth (up to 4% shorter than average people) and an increased risk of other birth defects.
Between the 18th week of pregnancy and birth, radiation-induced health effects (besides cancer) are unlikely unless the fetus receives an extremely large dose of radiation.
In the 18- to 25-week stage of pregnancy, health consequences similar to those seen in the 8- to 17-week stage could occur, but only when the doses are extremely large (more than about 5,000 chest x-rays received at one time). At this dose level, the mother could be showing signs of acute radiation syndrome, which is sometimes known as radiation sickness.
After the 26th week of pregnancy, the radiation sensitivity of the fetus is similar to that of a newborn.
At the 26th week of pregnancy, the fetus is fully developed though not fully grown. Unborn babies exposed to radiation in the womb during this stage of pregnancy are no more sensitive to the effects of radiation than are newborns. This means that birth defects are not likely to occur, and only a slight increase in the risk of having cancer later in life is expected.
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