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This module is for anyone who regularly handles veterinary medicines (e.g. when dispensing or administering them, including anaesthetic gases) or who might come into contact with blood, urine, faeces or vomit that might contain medicines or their metabolites. By doing this module you will:

  • understand how medicines can cause reproductive harm
  • understand how we get information about the harmful effects of medicines in pregnancy
  • know what practical measures to take to avoid harm
  • know where to find information on medicines and pregnancy.

A substance that can have harmful effects on reproduction is called a teratogen. Many medicines are known or suspected to have teratogenic effects. Harm can occur at any time from conception to birth. This can occur if a mother or father is exposed to a teratogen around the time of conception, or if the developing baby is exposed to a teratogen via the mother during pregnancy or around the time of birth. 

Depending on the teratogen and the timing of the exposure, the harm caused may include physical defects, fetal death, impaired fetal growth, effects on behavioural or neurological development, or even an increased susceptibility to diseases like cancer. 

There are several important factors that affect the likelihood of a teratogen causing harm.

  • Timing of the exposure. A human pregnancy usually lasts around 40 weeks, and is considered to have three main stages: the first, second and third trimesters. Although the main tissue and organ structures are formed during the first trimester (weeks 0 to 12–13), development and growth continues throughout the pregnancy and so harm can occur during any stage. It is important to be aware that the first sign of pregnancy is usually the first missed period, which is about 2 weeks after conception. So it is common for a woman to be unaware that she is pregnant for the first few weeks of her pregnancy. This is why it is so important to consider the potential for drugs to harm a fetus in all women who could potentially become pregnant.
  • Amount of drug and route of exposure. If a pregnant woman is exposed to a teratogenic medicine, the drug must cross the placenta in order to harm the fetus. It is logical that a drug the mother receives by mouth or injection will cross the placenta in larger amounts than if it has been in contact with her skin.
  • Ability to cross the placenta. Most medicines are able to cross the placenta; a few do not (e.g. large molecules such as heparin).
  • Individual variation. Women vary in how their bodies handle drugs. Similarly, unborn babies may vary in the way they respond to the effects of a drug.

It is difficult to be certain about the effects of a medicine in a human pregnancy. Some data comes from studies in pregnant laboratory animals. However, this is not very reliable for predicting what will happen in humans. Information also comes from reports of when women have taken medicines during pregnancy, either inadvertently or because it was a necessary treatment. Although this type of information can help, it does not usually allow a definite conclusion because it can be difficult to be certain that an adverse effect was caused by a medicine. 

When looking at the effects on people working with medicines, studies can be difficult to interpret because of changes in health and safety standards over time. However, there are two types of medicines used in veterinary practice for which there is good evidence, or a high level of suspicion, that they can cause harm during pregnancy: anti-cancer (cytotoxic) medicines and anaesthetic gases. 

There are no national guidelines specifically addressing exposure to occupational risk during pregnancy. However, the Control of Substances Hazardous to Health (COSHH) regulations require employers to control substances that are hazardous to health. To comply with COSHH regulations and prevent or reduce exposure to a hazardous substance, including medicines, all employers must:

  • assess the risks
  • decide what precautions are needed
  • prevent or adequately control exposure
  • ensure that control measures are used and maintained
  • monitor exposure
  • carry out appropriate health surveillance
  • prepare plans and procedures to deal with accidents, incidents and emergencies
  • ensure employees are properly informed, trained and supervised.

If a practice employs five or more people, the assessment(s) must be recorded in writing. Failure to adequately control hazards can lead to prosecution under the COSHH regulations and civil action from injured or ill employees.

Areas that need to be assessed in relation to occupational exposure to medicines include: general medicines handling; handling cytotoxic medicines; and spillage of medicines. All operating and recovery rooms should have effective and well-maintained ventilation or scavenging systems.

Anyone working in veterinary practice must follow these safety procedures when handling medicines.

  • Treat all medicines as potentially harmful.
  • Be aware of the hazards associated with medicines and know the results of the COSHH and risk assessments.
  • Wear disposable gloves when handling any open or loose products.
  • Be familiar with the practice’s standard operating procedure for handling medicines and use additional protective clothing and equipment when specified.
  • Inform the health and safety officer if they are, or expect to become, pregnant.
  • In the case of pregnancy, be aware of and avoid handling medicines likely to harm the unborn child, or medicines likely to cause miscarriage.
  • Inform the health and safety officer if they experience any allergies or adverse effects thought to be caused or made worse by the handling of, or exposure to, veterinary medicines.
  • Wash hands after handling medicines, even if disposable gloves have been worn. 

Only very limited evidence is available about occupational exposure to specific drugs. It is therefore difficult to provide useful information about the reproductive and developmental effects of such exposures. More information is available through people being treated with medicines. This type of exposure in the mother or father would be expected to produce higher body concentrations and hence higher rates of fetal exposure, but the information might be useful for assessing potential risks in people exposed to the medicine in other ways.

Clinical information on exposure during treatment is available to NHS health professionals from the UK Teratology Information Service (UKTIS) via a dedicated telephone advice service. However, it can only be provided to NHS health professionals. So anyone working in veterinary practice who is concerned should seek an appointment with a GP, midwife or obstetrician who can contact the service on their behalf.

UKTIS also produces written summaries of the fetal effects of maternal environmental exposure. A particularly useful one for veterinary employees is their summary on occupational exposure to cytotoxic medication. The UKTIS patient information website (called “bumps”, for Best Use of Medicines in Pregnancy) also offers free patient information leaflets on more than 200 medicines.

  • The term ‘teratogen’ is generally used for substances that can have harmful reproductive effects.
  • Harm can potentially occur at any time during pregnancy, including in the first few weeks when women commonly do not yet know they are pregnant.
  • Information about the effects of occupational exposure to veterinary medicines is extremely limited.
  • Veterinary employers must comply with COSHH regulations to prevent or reduce exposure to hazardous substances, including medicines.
  • All medicines, including anaesthetics, should be treated as potentially harmful.
  • Veterinary employees who are concerned about occupational exposure should either seek an appointment with a GP, midwife or obstetrician who can contact the UK Teratology Information Service (UKTIS) for patient-specific advice, or should look for information on the UKTIS or bumps websites.



You can listen to a complete podcast of the module by using the play button below or use the download link on the right-hand side of the player to download the podcast to your mobile device.



BSAVA. Health and safety in the dispensary [online]. Available: [Accessed 13.4.2018]

Health and Safety Executive. Safe handling of cytotoxic drugs in the workplace [online]. Available: [accessed 13.4.2018]

Health and Safety Executive. Control of Substances Hazardous to Health (COSHH) [online]. Available: [accessed 16.4.18]

A more detailed version of this module is published in Veterinary Prescriber