Australian Birth Defects Society

A Society devoted to the study of birth defects


Q: In an ideal world all pregnancies would be planned, however the reality is that around 50% of western pregnancies are unplanned. This can result in exposures occurring before the woman realises that she is pregnant, and often causes significant worry for both the pregnant woman and her health care providers.

Frequently these exposures do not increase the risk of either miscarriage or birth defects compared with the general population, and evidence based counselling can reassure those women with wanted pregnancies that considering termination is unnecessary.

Two common exposures are described below, where the reassurance can be provided based on DOSE. Next month look for scenarios where the defining issue is TIMING (gestational stage) of the exposure.


Women may be exposed to radiation from diagnostic procedures such as x-ray, CT scans, or within their workplace. Radiation is widely recognised as a human teratogen, which women are often acutely aware of – they will recall signs in the medical department asking “could you be pregnant?” and also being asked directly whether there is a possibility of pregnancy before the procedure is performed. This creates the impression that any radiation exposure in pregnancy is extremely dangerous, which is then sometimes echoed by the GP who diagnoses the pregnancy.

BUT… radiation is demonstrated to have a dose dependent effect on pregnancy, where low doses (as will be commonly encountered in diagnostic procedures) have not been shown to increase the risk of birth defects over that in the general population. Women exposed to diagnostic radiation doses can therefore generally be reassured that there is no need to consider termination of an unplanned but wanted pregnancy.

When a woman who has been exposed to radiation calls MotherSafe for advice, she will be advised to ask the Radiologist who performed the procedure to calculate a dose estimation, based on the investigation and machine settings used. It is only in exceptional circumstances that the exposure dose will be above what is considered the NOEL, or no observable effect level.

FLUCONAZOLE (available over the counter in Australia as a single dose to treat vaginal thrush).

Vaginal thrush is a common condition, which can be treated with locally acting vaginal creams and pessaries. Oral fluconazole taken as a single (low) dose of 150mg, has been marketed as an easy alternative for treatment, and is often chosen by women in preference to vaginal products for its convenience. MotherSafe regularly receives calls from women who have taken the single dose in early pregnancy, before they knew they were pregnant.

Fluconazole is believed to cause birth defects in humans if taken at high does (300-500 mg per day) and prolonged periods (weeks) in the first trimester, and for this reason carries a TGA pregnancy category D. On the basis of the pregnancy category, doctors and pharmacists will often perceive, and convey to the patient, that their risk of having a baby with a birth defect is high.

BUT… follow up of over 600 women who took low doses of fluconazole did not show any increase in risk for having a baby with a birth defect. Women who have inadvertently taken a single dose in early pregnancy may be reassured that their risk is felt to be no greater than that in the general population. A recent study has found that there may be a slightly elevated risk of miscarriage in women exposed to low dose treatment, so once pregnancy is diagnosed, vaginal products should be recommended as first line treatment

For specific information regarding your particular medications in pregnancy or breastfeeding call MotherSafe 02 9382 6539 or 1800 647 848 (from country NSW only).

Page updated 7 June 2017

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MotherSafe is a free telephone service for the women of NSW, based at the Royal Hospital for Women, Randwick.

Unplanned pregnancies: an exposure has occurred before the woman realises that she is pregnant