It is a study of Rx that is performed in pregnant women who are approximately between week 34 and 36 of gestation in order to measure the diameter of the pelvis to determine if the patient is able to give birth naturally.
It is not advisable to perform imaging studies with ionizing radiation in pregnant women unless it is a medium emergency, however, there are other alternatives such as magnetic resonance depending on the patient's circumstances
The safest thing to expose a pregnant woman to ionizing radiation is to do it after 5 months of gestation and in the case of CT scan, the entire abdominal area, pectoral and if possible the neck should be protected.