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Pregnancy & Radiological Examinations

Not all radiological examinations have radiation. Ultrasound examination does not involve harmful radiation. Magnetic Resonance (MR) examination also does not involve harmful radiation. However, the long term effects of strong magnetic field on fetuses are not known.


MR & Pregnancy
Radiation & Pregnancy

Effects of Radiation

In early pregnancy the cells of the unborn child are diving rapidly, and large doses of radiation can be hazardous. Therefore pregnant women should avoid exposure to x-rays if at all possible. The effect of radiation can be viewed in relation to the stages of human development. According to the American Association of Physicists in Medicine (AAPM), a unborn child exposed to 1 rem of radiation has less than one chance in a thousand of suffering birth defects as a result of the exposure, even if exposed during the most critical stages of development (3 to 8 weeks of pregnancy). The "natural" risk of congenital defect is much greater than any potential added risk from the x-rays.

A.Fetus (During Pregnancy): pregnancy progresses in 4 recognized stages

  • a. Pre-implanation: About 50% to 75% of all human pregnancies abort (Boklage, 1990). The vast majority of these are unrecognized because they abort at or before the next expected menstruation (Wilcox et al, 1988). The cause of most of the aborted pregnancies appears to be abnormal development. Radiation exposure at this stage would result in Malformation or Pre-natal death. Human data is limited to very high doses (> 100 rad) received after implantation. Animal data suggest that radiation-induced prenatal death might occur at doses of 5 to 10 rad if delivered prior to implantation. However, this effect has not been observed for humans who have received diagnostic level doses.
  • b. 1st trimester: About 15% to 20% of clinically diagnosed pregnancies abort in the first or early-second trimester. Many of the effects of radiation were observed from the survivors of Japanese A-bomb. Based on Japanese A-bomb survivors, no adverse effects were observed if the conceptus was irradiated prior to 8 weeks postconception or after 25 weeks.

    i. Embryonic period (8-56 days postconception): Based on Japanese A-bomb survivors, doses to the conceptus greater than 25 rad during this period are associated with an increased probability of the offspring being born on average 2 to 3 cm shorter, about 3 kg lighter, and with a smaller (~1 cm) head circumference than normal. Thus, radiation at this stage may result in Growth Retardation

    ii. Early fetus (2-15 weeks postconception): Radiation at this stage may cause neurologic, intellectual, or mental deficit, or seizures. During the first 15 weeks after conception the induced incidence of small head size during the period was about 0.5% to 1% per rad delivered to the conceptus. There was no obvious threshold. The incidence of severe mental retardation (SMS) or decline in IQ for exposures from 8 through 15 weeks postconception was about 0.4% per rad delivered to the conceptus. There is a threshold of 1 rad.& 10 rad respectively. No increase in SMR was observed for irradiation occurring in the first 7 weeks postconception or after the 25th week. Only those exposed to more than 10 rad in the period of 8 to 15 weeks postconception demonstrated a statistically significant increase in seizures, mostly among those with SMR.

  • c. 2nd & 3rd trimester: Radiation may increase the risk of malignancy. The increase in childhood cancer is 1-2 cases in 3000 children each exposed in utero to 1 rad.

The risk to the baby is practically nil for the following exposures:

  • dental x-rays, even without a lead apron
  • barium enema, IVU
  • x-rays to the fathers testicles just prior to conception
  • working as an x-ray technologist (following good radiation safety guidelines)
  • living near a nuclear power plant

Conventional radiography of the extremities, head, and thorax, and computed or conventional tomography of the head deliver minimal amounts of ionizing radiation to the uterus and any medical benefit from them outweighs the surmised risks even if the patient is pregnant

The potential for adverse radiation effects are substantially higher if the conceptus is in the x-ray field than if the conceptus is outside the x-ray field. When the conceptus is in the x-ray field the majority of the dose is from the primary x-ray beam. When the conceptus is outside the x-ray field there are two components to the dose, scatter and leakage radiation. The distance between the conceptus and the edge of the x-ray field and the density of the intervening tissue affects the dose from scatter radiation. The distance between the x-ray tube and the conceptus affects the dose from leakage radiation.

It is interested to note that radiation risks to fetus, during flight for casual travelers under normal solar conditions, is negligible. However, there is an irregular space-weather phenomenon called a solar-particle event. These are infrequent and usually short-lived, but they can significantly change the radiation dose while in flight to levels that can easily surpass the 1 mSv exposure limit, even for a single trip.


Recommendations.for pregnant ladies exposed to radiation

a. If the conceptus is exposed to diagnostic levels of radiation during or prior to the first two weeks postconception (<14 days) therapeutic abortion is not advised.

b. For patients exposed to diagnostic levels of radiation between the second and eighth conception weeks (days 14-56):

  • Therapeutic abortion based solely on radiation exposure is not advised for doses less than 15 rad.
  • Only if there are other compromising factors severely threatening the mother or conceptus, (eg. acute viral disease, teratogenic drug use, severe pulmonary hypertension) should the additional risks from radiation doses in excess of 5 rad be considered a factor in deciding future care. Doses exceeding 15 rad may be an indication for therapeutic abortion in the presence of less severely compromising factors. However, diagnostic studies rarely result in such dose levels.

c. For conceptuses exposed between the 8th and 15th week postconception (days 56 to 105):

  • (1) At doses below 5 rad, radiation should be considered a minor teratogenic factor and does not, by itself, represent a sufficient risk to justify therapeutic abortion.
  • (2) For doses between 5 rad and 15 rad, therapeutic abortion is not advisable on the basis of the radiation risk alone. If other compromising circumstances exist, radiation exposure should be considered only as one of the contributing agents to the overall risk.
  • (3) At doses above 15 rad in this time interval there is scientific evidence that may support a recommendation for therapeutic abortion based on the radiation exposure. However, this does not mean an abortion is necessarily recommended. Based on current data the following is a summary of potential risks:
    • (a) At 15 rad, there may be up to a 6% chance that the child could be mentally retarded. Conversely, there is at least a 94% chance the child will not have such a radiation- induced anomaly.
    • (b) The chance that the child will develop cancer is less than 3%. Conversely, the child has better than a 97% chance of not developing cancer.
    • (c) The chance of having a small head size is approximately 15%, but this does not necessarily affect normal mental function.
    • (d) The child's IQ may be a few points short of its full potential
    • (e) Except for possible effects to individual organs from specific radionuclide studies, no other risks have been demonstrated
  • (4) Therapeutic doses of 131I delivered during this time may represent a severe compromise to fetal thyroid function and may result in hypothyroidism and cretinism, which could be grounds to recommend therapeutic termination. Careful analysis of the potential for this effect (Fisher et al., 1963) is strongly recommended

For further information, please see Exposure of the Pregnant Patient to Diagnostic Radiations �V A Guide to Medical Management" Second Edition, by Louis K Wagner, Richard G. Lester, and Luis R. Saldana, 1997, Medical Physics Publishing, Madison, Wisconsin & http://www.mamc.amedd.army.mil/preventive_med/hpo_pregnancy.htm

 

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