pregnancy_rad

fetal radiation doses in pregnancy Xrays and CT scans

see also:

Introduction

  • the risk-benefits of radiologic investigations in pregnancy and lactation need to be considered
  • exposure of less than 50mGy at any gestation is associated with negligible additional risk to the fetus although they may be an increased life time risk of cancer, for example, a 10-20mGy dose to a fetus may give a 1.5-2.0x risk of childhood leukaemia but the background rate is 1 in 3000 so absolute risk is small.
  • there is no evidence of teratogenic or mutagenic risk with iodinated contrast and no cases of fetal or neonatal hypothyroidism have been reported, these are also safe in lactation as only 0.01% of maternal dose is absorbed by the infant in breast milk
  • gadolinium contrast is also safe in lactation as 0.0004% of maternal dose is absorbed by the infant in breast milk
  • MRI in any trimester does not seem to confer harm to the fetus or infant

Estimated threshold radiation doses for fetal injury

gestation threshold radiation dose (mGy)
congenital anomalies or growth restriction during organogenesis (4-10wks gestation) 200
intellectual disability 10-17wks gestation 60-310
intellectual disability 18-27wks gestation 250-280

Estimated fetal doses

modality est. fetal dose (mGy)
CXR / head Xray <0.0001
AXR 0.1-3.0
CT head 1-10
CT chest/liver or CTPA 0.01-0.7
CT abdomen 1-10
CT abdo pelvis 10-50
V/Q scan 0.1-0.5

NB. external lead shielding of maternal pelvis reduces radiation dose by ~3% at all stages of pregnancy 1)

maternal risks of radiation exposure

  • breast exposure during pregnancy or lactation:
    • CTPA gives 20-70mGy breast exposure compared to ~0.25mGy for V/Q scan (ie. over 100x dose)
      • CTPA dose can be reduced by up to a third by use of a bismuth breast shield &/or organ-based tube current modulation
      • those with a normal CXR should be offered V/Q scan rather than CTPA
1)
Circulation 2001; 104:893-7, Damilakus et al
pregnancy_rad.txt · Last modified: 2019/01/06 07:00 by wh