Minimising potential fetal radiation



10 day rule

For a patient who has a regular 28 day menstrual cycle, the procedure should be scheduled to take place during the first 10 days of the menstrual cycle.

Date of LMP = 1st day of the LMP.

28 day rule

  • Procedure can procede if the patient's menstrual period is not overdue and the patient has indicated she is not pregnant

Postmenopausal

  • No periods x1 yr if >50yo or
  • No periods x2 yr if <50yo or
  • No period x2 yrs if <50yo and no hormonal contraception

Preg. Declaration Form

Women of childbearing age undergoing a low or low (below) fetal dose procedure are asked to complete a Pregnancy Status Declaration Form (below) indicating pregnancy status and date of LMP. These questions should be completed by a patient if she has missed a period, if periods are absent or in the case of high fetal dose procedures if the patient's date of LMP does not fall within the last 10 days.


High fetal Dose

10 day rule applies

  • Any CT betw. diaphragm & pubis, except CT L Spine
  • CT Elbow/ Wrist if placed near abdomen

Low fetal Dose

28 day rule applies

  • XR or CT abdomen
  • CT lumbar spine


Content by Dr Íomhar O' Sullivan. Last review Dr ÍOS 20/10/25.