22 - obstetrics cases - MCQ1

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.