Some medicines are known or suspected to have teratogenic potential (potential to increase the risk of birth defects and development disorders) when taken during pregnancy, especially during the first trimester.The product information advises that pregnancy should be avoided during treatment, when using any medicine with teratogenic potential, a woman should be advised of the risks and encouraged to use the most effective contraceptive method.
Contraceptive methods are designated as effective or highly effective based on their failure rates in typical use in the first year. Highly effective methods have typical-use failure rates >1% and include male or female sterilisation and long-acting reversible contraceptive (LARC) methods. Progestogen-only injections have a typical-use failure rate of 6%, but this may be due to repeat injections being administered late. Other effective methods include combined hormonal contraceptive and progestogen-only pills, which have typical-use failure rates of 9%.
A woman may be unaware of her pregnancy at treatment initiation or be in early stages of pregnancy at the time of repeat prescribing due to contraceptive failure. MHRA received reports of inadvertent exposure to such medicines during early pregnancy. Inadvertent exposures can be avoided if a pregnancy test is performed before prescription of a teratogenic drugs.
The Medicines for Women’s Health Expert Advisory Group of the Commission on Human Medicines has developed an aide-memoire table to provide guidance to prescribers of teratogenic drugs on the frequency of pregnancy testing needed to avoid exposure in pregnancy during treatment, depending on the chosen contraceptive method. The aide-memoire table provides a summary of the pregnancy testing advice for the most common contraceptive methods. The table is colour-coded according to the most reliable methods.
If pregnancy cannot be excluded, the treatment decision will depend on individual circumstances. If feasible, treatment with a teratogenic drugs should be delayed until pregnancy has been excluded by a repeat test.
This guidance was produced by the MHRA in consultation with advisory committees the Commission on Human Medicines and Medicines for Women’s Health Expert Advisory Group. Recommendations are based on FSRH statement on teratogenic drugs and contraceptive failure rates in typical use.