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