The development of a fetus is an exquisitely choreographed series of events that need to occur at the right time in order for the baby to grow properly. Radiation can have a multitude of effects on this. The timing of the radiation exposure and the dosage both have an impact on how the fetus will respond.
Radiation and Biology
When cells are exposed to radiation, three things can happen, explains the United States Nuclear Regulatory Commission. The cells may die off and get replaced just like cells normally do every day, the cells may utilize cellular repair mechanisms to fix any damage that occurs or the cells may incur major damage that leads to long-term effects.
Doses
According to Duke University, a total dose of less than 1,000 millirems has no noticeable effect on fetal development. Doses between 1,000 and 10,000 millirems confer a slight level of risk for some problems, but most fetuses who receive less than this amount will be fine. At 10,000 millirems of radiation, or 10 rems, the likelihood of problems increases. The minimum threshold for mental retardation is about 15 rems, while at 30 rems, mental retardation is likely to occur. Diagnostic scans such as x-rays give less than 10 rems of exposure.
Early Pregnancy
Fetal development is most vulnerable to the effects of radiation between weeks two to 15 of the pregnancy, according to the Centers for Disease Control and Prevention, or CDC. During the first two weeks of development, the pregnancy may miscarry or the baby will continue growing with no ill effects. Developmental abnormalities due to radiation this early in pregnancy are rare. Women who were between eight and 15 weeks pregnant during the nuclear bombings of the Japanese cities Hiroshima and Nagasaki in World War II had children with severe mental retardation, lowered IQ and stunted growth that made them four percent shorter than others their age, indicating that this is the most vulnerable time during development for radiation exposure.
Late Pregnancy
In women who were between weeks 16 to 22 of pregnancy during the nuclear WWII bombings in Japan, radiation doses that were high enough to cause acute radiation sickness in the mother could cause the baby to experience similar developmental issues as the eight to 15 week fetuses. Babies who encountered lower doses were not affected. Babies exposed after 26 weeks development had risk profiles similar to newborns exposed to radiation and did not have any additional developmental problems.
Long-Term Effects
Radiation exposure during development also raises long-term risks of some diseases. The most prominent is a rise in the cancer risk for individuals exposed to radiation in the womb. However, the CDC maintains that this risk is small, less than a two percent rise with radiation exposure equivalent to 500 x-rays.
