Answer to Question #852 Submitted to "Ask the Experts"

Q

I am a radiologist in Thailand. I have a case of a women who is 24 years old. She complained of dyspepsia and nausea. She met with her medical doctor. She told him that she had a normal menstrual cycle. The doctor sent her for an upper GI study. After eight weeks she complained of a mass in her lower abdomen and again the same doctor now sent her for a sonogram of her lower abdomen. Then pregnancy with gestational age of about 18+ weeks was diagnosed. When we trace back to the upper GI study the gestational age would have been about 10 weeks. The dose rate was not measured for the fluoroscopic machine. But this machine uses a good film-screen method. What should be my suggestion to the obstetrician and the patient?

A

Thank you for the question. First, as you're probably already aware, there is no radiation dose to the fetus from the ultrasonography so I'll keep my comments on the upper GI study. According to Wagner, et al, a typical dose from an upper GI study to the uterus is 1 mGy (100 mrad) (Wagner, 1997). There is a reported range of 0.05-12 mGy (5-1200 mrad) (Wagner, 1997). The uterus is an appropriate reference organ at a gestation of 10 weeks. At this stage of pregnancy, 60 mGy (6000 mrad) is the lowest reported radiation dose shown to cause biological effects in the fetus. In fact, once beyond week eight, fetal sensitivity is much less than between weeks one and eight. Wagner, et al., state that "at fetal doses below 5 rad, radiation should be considered only a minor teratogenic factor and does not, by itself, represent a sufficient risk to justify therapeutic abortion." This recommendation is in good company. The National Council on Radiation Protection and Measurements states: "The risk of abnormality is considered to be negligible at 5 rad or less when compared to other risks of pregnancy, and the risk of malformations is significantly increased above control levels only at doses above 15 rad. Therefore, exposure of the fetus to radiation arising from diagnostic procedures would very rarely be cause, by itself, for terminating a pregnancy." (NCRP 1977). The suggestion to the obstetrician and the patient is that there would be very low risk if any for the baby from these low doses. References:

• Wagner L.K; Lester R.G.; Saldana L.R. Exposure of the pregnant patient to diagnostic radiations: A guide to medical management. 2nd Edition. Madison, WI: Medical Physics Publishing; 1997.
   
• National Council on Radiation Protection and Measurements. Medical radiation exposure of pregnant and potentially pregnant women. Washington, DC: NCRP; NCRP report No. 54; 1977.

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