Pre-conception irradiation of either parent's gonads has not been shown to result in increased cancer or malformations in their children. The noncancer effects of ionizing radiation on the embryo or fetus depend on the radiation dose and the gestational age at the time of exposure. Effects of ionizing radiation on the embryo or  fetus include , miscarriage, fetal growth restriction, congenital malformation (e.g. microcephaly), mental retardation, and increased risk for childhood cancer [1].

Radiation-induced noncancer health effects are not detectable for fetal doses below about 50 mGy (1 mGy =100 mrad) [2]. Noncancer health effects may be expected after fetal doses >=100mGy and appear to have the most significant effects between the gestational ages 8-25 weeks.  Doses > 100mGy are not commonly reached with conventional x-ray examinations, but may be reached with fluoroscopic procedures (e.g. barium enema) and with radiotherapy (Table 1).

Table 1. Maximum Estimated Fetal Dose (mGy) During Some Common
              Diagnostic Imaging Studies

* 10 slices with slice thickness = 10mm
† The use of radioactive isotopes of iodine is contraindicated in pregnancy

Prior to 2 weeks gestation an exposure of 100 mGy (10 rads) may lead to death of the embryo. The dose necessary to kill 100% of human embryos or fetuses before 18 weeks’ gestation is about 5000 mGy (500 rads). Radiation-induced noncancer health effects are unlikely at this stage of development no matter what the radiation dose. [2].

For fetuses exposed between 8-15 weeks' gestation atomic bomb survivor data indicate that the decline in IQ score is approximately 25–31 points per 1000 mGy above 100 mGy ( 40% risk for severe mental retardation) [9].

From 16- to 25 weeks' gestation the average IQ loss is approximately 13–21 points per 1000 mGy (per 100 rads) at doses above 700 mGy (70 rads) [2].

After 26 weeks, doses above 1000 mGy (100 rads) the risks for stillbirth and neonatal death (i.e., infant death within 28 days after birth, including stillbirth) increases [2].

There appears to be slightly increased risk of childhood cancer with radiation doses to the fetus of >= 10mGy (1000 mrad). There is no evidence that this effect is dependent on gestational age. The absolute risk for fatal cancer for ages 0-15 year after prenatal radiation exposure has been estimated to be 0.006% per 1 mGy. For the whole life span this risk is about 0.015% per 1 mGy. In other words there is over a 99% chance that a fetus exposed to less than 100mGy will NOT develop childhood cancer or leukemia

Recommendations International Commission on Radiological Protection (ICRP)

• All medical practices (occupational and patient-related) should be justified (more benefit than risk).
• A missed period in a regularly menstruating woman should be considered due to pregnancy, until proven otherwise.
• Pregnant medical radiation workers may work in a radiation environment as long as there is reasonable assurance that the fetal dose can be kept below 1 mGy during the pregnancy.
• The pregnant patient or worker has a right to know the magnitude and type of potential radiation effects that might result from in-utero exposure.
  • Communication should be related to the level of risk. Communication that risk is negligible is adequate for very low dose procedures (<1 mGy to the fetus)
  • If fetal doses are above 1 mGy, a more detailed explanation is appropriate.
• After it is decided to do a medical radiation procedure, the fetal radiation dose should be reduced while still obtaining the required diagnostic information.
• Termination of pregnancy at fetal doses of less than 100 mGy (10,000 mrad) is NOT justified based upon radiation risk
• At fetal doses between 100 and 500 mGy, decisions should be based upon individual circumstances
• At fetal doses in excess of 500 mGy, there can be significant fetal damage, the magnitude and type of which is a function of dose and stage of pregnancy

In summary women who have had routine dental x-rays, plain films of the head, extremities, and chest (including mammograms), or computed tomography (CT) of the head or chest may be counseled that there is no increased risk to their fetus of  miscarriage, fetal growth restriction, congenital malformation (e.g. microcephaly), or mental retardation. In addition they may be counseled that there is > 99% chance that their child will NOT develop a childhood cancer.

For patients who have had fluoroscopic studies, studies involving radioactive isotopes,  or radiotherapy the fetal radiation dose should be estimated by qualified medical personnel to provide a more detailed approximation of risks to the fetus. Consultation with hospital medical physicists or a health physicist should be considered.

REFERENCES

1. Valentin J, Editor, Annals of the ICRP, Publication 84: Pregnancy and Medical Radiation, International Commission on Radiological Protection, Volume 30, No. 1. Tarrytown, New York: Pergamon, Elsevier Science, Inc., 2000.
2. Prenatal Radiation Exposure: A Fact Sheet for Physicians (CDC) http://www.bt.cdc.gov/radiation/prenatalphysician.asp
Accessed 11/5/03
3. National Council on Radiation Protection and Measurements. Medical radiation exposure of pregnant and potentially pregnant women. NCRP Report no. 54. Bethesda, Md.: The Council, 1977. 
4. Osei EK, Faulkner K.Fetal doses from radiological examinations. Br J Radiol. 1999 Aug;72(860):773-80.  PMID: 10624343
5. Cunningham FG, MacDonald PC, Gant NF, Leveno KJ, Gilstrap LC, eds. Williams Obstetrics. 20th ed. Stamford, Conn.: Appleton & Lange, 1997:1045-57
6. Winer-Muram HT, Boone JM, Brown HL, Jennings SG, Mabie WC, Lombardo GT.Pulmonary embolism in pregnant patients: fetal radiation dose with helical CT. Radiology. 2002 Aug;224(2):487-92. PMID: 12147847
7. Brent RL, Gorson RO. Radiation exposure in pregnancy. In: Current Problems in Radiology. Technic of pneumoencephalography. Chicago: Year Book Medical, 1972:1-47.
8. Ginsberg JS, Hirsh J, Rainbow AJ, et al. Risks to the fetus of radiologic procedures used in the diagnosis of maternal venous thromboembolic disease. Thromb Haemost 1989;61(2):189-96 PMID: 2749594
9. Schull WJ, Effects of Atomic Radiation, A Half-Century of Studies from Hiroshima and Nagasaki. New York: Wiley-Liss & Sons, Inc., 1995.
10. Kal HB, Struikmans H. Pregnancy and medical irradiation; summary and conclusions from the International Commission on Radiological Protection, Publication 84 Ned Tijdschr Geneeskd. 2002 Feb 16;146(7):299-303

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