Radiation and Pregnancy

Effects upon the fetus

The effective dose to an irradiated fetus is the most important type to consider. It is approximately equal to the absorbed dose (measured in mGy) or equivalent dose (measured in mSv) to the patient’s uterus.

DOSE LIMIT TO FETUS: 1mSV after pregnancy is declared

• Fetus is declared member of the public
• In practice staff member should receive less than 2mSV to surface of abdomen.

Deterministic effects

Deterministic effects of practical significance typically require foetal
doses > 100 mSv (ICRP, 2007)

Termination of a pregnancy is not recommended for foetal doses
below 100 mSv (ICRP, 2000)
 Normal diagnostic exposures (x-ray / radionuclide) should NOT result
in foetal doses of this magnitude

Miscarriage or fetal death

Radiation doses of 100–500 mGy in the first few weeks after conception are associated with an increased risk of fetal death. In animal studies high doses are associated with failure of implantation.

Neurological effects

Nervous system abnormalities characterised by reduced IQ and a higher frequency of severe mental retardation, occur at high radiation doses.

There is a non-linear dose response relationship for neurological effects with a high frequency of abnormalities at radiation doses of 500 mSv to the brain with a lower rate of abnormalities at 100-200 mSv. There appears to be a threshold for neurological effects with no evidence of abnormalities at doses less than 100 mSv. Neurological effects mainly occur with irradiation between 8 and 25 weeks’ gestation with the highest risk during the 8 to15 week period.

Genetic effects

The risk of heritable effects from fetal irradiation is very low, being much lower than the risk of
radiation induced carcinogenesis, and also very much lower than the natural risk of heritable
disease3. The natural frequency of heritable disease manifesting at birth is 1-3%, or 5-6% if
minor or uncertain congenital abnormalities are included3,5,7.
3.5 Gonadal irradiation
Preconception irradiation of either parent’s gonads has not been shown to result in increased
cancer or malformations in their children2

Stochastic effects

Carcinogenesis

• Doses of 10 mGy or higher to the fetus are likely to cause a small increase in the risk of childhood cancer and leukaemia.
• Doses of 10 mGy or greater, the excess risk is 6% per Gy; i.e., the excess risk per mGy up to the age of 15 years, is estimated to be 1 in 17,000 for induction of cancer or leukaemia.
• The excess risk per mGy for death from cancer or leukaemia is 1 in 33,000
• For comparison, in the UK the baseline risk of cancer or leukaemia in the first 15 years of life is about 1 in 650 (0.15%)
  The risk of cancer induction for a given fetal effective dose is considered to be uniform throughout pregnancy after the first 3-4 weeks of gestation (5-6 weeks from LMP). There is some controversy about the relative risk in the first 3-4 weeks of gestation.
• Radiation has been shown to cause leukemia and many types of cancer in both adults and children. Throughout most of pregnancy, the embryo/fetus is assumed to be at about the same risk for potential carcinogenic effects of radiation as are children.

Considerations for the Pregnant Patient

Consider whether a non-ionising technique is possible
(US, MRI) or a lower-dose technique (e.g. plain film
instead of CT)
2. If proceeding with an x-ray:
 Try to avoid primary irradiation of foetus (not always
possible!)
 Collimate
 Use lead drapes over foetal region
 Choose views / projections / angles which limit dose to foetal
region

Radiation dose to your fetus can be measured and estimated. The measure we use is called milligray
(mGy). A CT scan of any part of the body other than your abdomen will typically expose your baby to
less than 2 mGy of ionising radiation.
The two types of risks to the unborn baby from ionising radiation exposure are:

1. Risks of malformations, intellectual disability, growth retardation or death
These effects are seen only with doses of 100 mGy or more. These are very high doses that do
not occur with diagnostic radiology procedures and tests. Therefore, there is no risk of these
problems for your baby as a result of diagnostic x-rays or CT scans.

2. Risks of childhood cancer
20 in every 10,000 (or 1 in 500) children who have had no ionising radiation exposure as an
unborn baby will be diagnosed with cancer sometime before the age of 18. This is the natural
rate of childhood cancers.
There is evidence that direct exposure of the unborn baby to medical x-rays can increase this risk but
only with direct exposure of your baby, for example with a CT scan or x-ray of your abdomen
or pelvis.
With most diagnostic radiological procedures, that do not involve direct exposure of your baby to the
x-ray beam (for example a chest x-ray, head or chest CT scan, mammogram, or an x-ray of your
neck, chest, arm or leg) your baby would receive less than 2 mGy of radiation exposure. The
theoretical risk of childhood cancer in this case would increase from 20 in every 10,000 to 21 in every
10,000. This is a very small increase.
With procedures that directly expose your baby to the x-ray beam during an abdominal CT, the dose
to your baby is likely to be around 20 – 50 mGy. However, this needs to be calculated by a specialist
medical radiation because the dose will vary depending on the kind of scan you are having (or have
had). This calculation will provide a more accurate estimate of exposure of your baby. This
information can be provided to you and your doctor by a specialist medical physicist.
With doses between 20 – 50 mGy, the theoretical risk of childhood cancer may be up to 40 in every
10,000 or 1 in 250.
You should feel free to discuss the following with your medical team if your test is not a medical
emergency:
• Why the test is required
• What questions will be answered by having the test
• What alternatives tests are there, if any, that do not involve ionising radiation that could also
answer these questions
• What would happen if you d