Nothing causes panic like the words “radiation exposure”. The earthquake and tsunami that devastated Japan also caused major damage to several nuclear reactors and have magnified our fears about the risks of radiation poisoning.

Radiation studies from past catastrophes such as Hiroshima and Nagasaki, (1946) Three Mile Island, (1979) and Chernobyl, (1986) have helped us determine the amount of radiation exposure that is considered safe. Still, many of the answers have yet to be determined, especially for pregnant women. Therefore, I thought it important to share some information about radiation exposure with specific regard to the fetus and pregnancy.

1) How is radiation released in a nuclear reactor?

Nuclear reactors use uranium or plutonium to produce energy that heat water to steam which turns turbine generators. Radioactive by-products are released in the process of producing this energy. The core, where this energy is created, has a cooling system surrounded by a steel canister and a surrounding concrete envelope. When damage occurs to a nuclear reactor the cooling system can get damaged and the surrounding protective structures can be damaged by explosions and elevated temperatures. The radioactive material in the core can then escape releasing radioactive material into the environment.

2) Who will be affected by the release of radiation?

Exposure can occur directly to employees or emergency individuals who work within the plant itself. Skin and/or deep internal organs can be affected depending upon dosage and type of radiation released.

Radioactive products can also leave the plant and reach people living in the surrounding region. Both skin or internal organs can be involved depending upon dosage and type of product released.

Internal contamination occurs when radioactive by-products are ingested from contaminated water, fruits, vegetables, and seafood inhaled, or enter the body through an open wound. Large numbers of individuals can get radiated in this fashion.

3) Why is radiation dangerous?

Radiation exposure can cause DNA damage resulting in death of cells. Mutations can alter developing cells or cause changes in reproductive cells which can get passed onto future generations. This damage can have both short and long term effects on every organ system in the body. Results can be manifested as deformities, congenital malformations, fetal loss, stillbirths, infant deaths, stunted growth, abnormal brain development, or cancer later on in life. Damage is dependent on the type of radiation, the dosage, length of time of exposure, the particular tissue exposed, and the depth of penetration.

Babies have some added protection being shielded inside the mother so their radiation exposure is less.

4) How is radiation dosage measured?

Radiation is measured in rads, the amount of energy deposited per kilogram of tissue. Gy is also used which refers to the absorbed dose and Sv (sievert) or the effective dose (the absorbed dose multiplied by the sensitivity of tissues and the biologic effect of different types of radiation)

One hundred rads is equal to 1 Sv or 1 Gy

5) What are some of the typical dosages of radiation that people are normally exposed to?

Reference: ACOG Committee opinion: Sept 2004; NEJM April 2011

6) Is exposure to x-ray or imaging procedure during pregnancy safe?

Exposing a pregnant woman to diagnostic x-ray procedures should only be performed when the benefits outweigh the risks. A single x-ray procedure does not warrant any significant risk to the fetus according to the American College of Radiology. If multiple x-rays are warranted, dosages of total exposure can be calculated by a specialist. Risks are related to dosage and to gestational age of the fetus.

It appears that exposure between 8 to 15 weeks provides the greatest risk, especially for central nervous system defects.

Procedures with less than 5 rads, as in most diagnostic procedures, generally are not considered problematic.

It is estimated that exposure to 1 to 2 rads can increase the risk of leukemia by 1.5 to 2 fold.

Radiation exposure during the first 2 weeks of pregnancy mostly carries a risk of fetal death if  greater than 100 mGy or 10 rads since organ formation occurs afterward (3 to 5 weeks post conception).

Radiation exposure between 2 and 18 weeks is the most critical time because of the high radiation sensitivity of the developing central nervous system which can be severe. Results from studies of atomic bomb survivors demonstrated mental retardation, lower IQ scores, skeletal anomalies and other birth defects.

Exposure from 18 to 25 weeks can have similar effects occur similar to those previously described when the dosages are extremely large.

After 26 weeks, the risk is mostly the increased chance of having cancer later on in life rather than birth defects. The cancer most commonly observed is leukemia.

Imaging procedures using ultrasound and magnetic resonance imaging (MRI) should always be used preferentially over x-rays since there are no known adverse effects. Use of radioactive iodine is contraindicated in pregnancy. If a woman has been exposed to radioactive iodine, she should wait 4 to 6 months before trying to conceive.

Are X-ray machines at the airport safe during pregnancy?

The x-ray machines at the airport are shielded and there is no increased risk to pregnant passengers.

Are tanning beds dangerous to the fetus?

Tanning beds use concentrated ultraviolet A radiation which is very superficial and does not penetrate through the skin to the fetus. It is therefore considered safe in pregnancy.

Is it safe for pregnant women to fly?

Commercial flights expose passengers to cosmic rays in the atmosphere. Flights at latitudes close to the magnetic poles, such as international flights between Canada and European countries have radiation doses that are higher in comparison to short-distance flights at lower altitudes and latitudes. Calculations of radiation received during a flight can be calculated using the website http://www.helmholtz-muenchen.de/epcard

It is recommended that cosmic radiation dose to a fetus not exceed 1 mSv , or 2 mSv to a woman during the entire pregnancy. A pregnant air flight attendant may have to modify her schedule to ensure that this requirement is met. Generally, during a commercial flight the average dose of radiation to a fetus is 5.28 uSv (this is half the dose that the mother receives). A pregnant crew member can travel by air for approximately 190 hours during the entire pregnancy safely. The 2 mSv limit would be exceeded after 8 round trip flights from Canada to Germany.

It can be assumed that the casual traveler has minimal radiation exposure when traveling by air during pregnancy.

Summary:

Radiation risks are determined by a combination of stage of pregnancy and dosage. Significant risks occur when organs are forming and decrease with each trimester.

Dosages below 50 mGy, 10 mSv or 5 rads are considered safe.

Termination of pregnancy might be considered for dosages of radiation between 100 and 500 mGy, based on individual circumstances.

Dosages above 500 mGy have been found to have significant fetal damage.

Further research is necessary to determine if chronic lower dosages may also cause significant effects.

Central nervous system is particularly sensitive between 8 to 15 weeks to radiation effects.

Important diagnostic procedures involving radiation can be done if the benefit far outweighs the risks, but MRI and ultrasound should be done preferentially.

Lead shields can be worn during an x-ray procedure to reduce exposure to the fetus.