MCQ: A 24-year-old woman is in a car accident and is taken to an emergency
room, where she receives a chest x-ray and a film of her lower spine. It is
later discovered that she is 10 weeks pregnant. She should be counseled that
a. The fetus has received 50 rads
b. Either chorionic villus sampling (CVS) or amniocentesis is advisable to check
for fetal chromosomal abnormalities
c. At 10 weeks, the fetus is particularly susceptible to derangements of the central
nervous system
d. The fetus has received less than the assumed threshold for radiation damage
e. The risk that this fetus will develop leukemia as a child is raised
The answer is d. (Gleicher, 3/e, p 163.) While a 50-rad exposure in the
first trimester of pregnancy would be expected to entail a high likelihood
of serious fetal damage and wastage, the anticipated fetal exposure for
chest x-ray and one film of the lower spine would be less than 1 rad. This
is well below the threshold for increased fetal risk, which is generally
thought to be 10 rads. High doses of radiation in the first trimester primarily
affect developing organ systems such as the heart and limbs; in
later pregnancy, the brain is more sensitive. The chromosomes are determined
at the moment of conception. Radiation does not alter the karyotype,
and determination of the karyotype is not normally indicated for a
24-year-old patient. The incidence of leukemia is raised in children receiving
radiation therapy or those exposed to the atomic bomb, but not from
such a minimal exposure as here.
