Use of teratogenic medicines in females- updated MHRA guidance

25 Mar 2019

The MHRA has issued a drug safety update on contraceptive methods and pregnancy testing in women taking teratogenic medicines

The Medicines & Healthcare products Regulatory Agency (MHRA) has published a drug safety update to reduce accidental exposure of teratogenic medicines in pregnant females. Some medicines are associated with the potential to increase the risk of birth defects and developmental disorders (teratogenic potential), particularly in the first trimester of pregnancy. All women of child-bearing age should be made aware of the potential risks and advised on the most effective contraceptive methods where appropriate.

The MHRA has highlighted:

  • The importance of using highly effective or effective contraceptive methods
  • The effectiveness of a contraceptive method is determined based on its failure rate in typical use during the first year; “typical use” includes user errors such as missed pills or circumstances that may reduce contraceptive efficacy such as interactions with concomitant medicines
  • Highly effective contraceptive methods have a failure rate of less than 1% and include intrauterine devices/ implants and male or female sterilisation; effective contraceptive methods are defined as having typical-use failure rates of 9% and include progestogen-only pills and combined hormonal contraceptives in all forms
  • Barrier contraceptive methods and fertility awareness are not considered to be effective methods and should not be used alone
  • A recommendation for regular pregnancy testing to take place prior to issue of each prescription of a medicine with teratogenic potential to avoid accidental exposure

The Medicines for Women’s Health Expert Advisory Group of the Commission on Human Medicines has developed a guidance table of teratogenic medicines with direction on the frequency of pregnancy testing depending on the selected contraceptive method. The following key factors were used to produce the guidance for prescribers:

  • The chances of a woman becoming pregnant can be affected by her circumstances during treatment; a pregnancy test should therefore be carried out prior to issue of each prescription of a teratogenic medicine
  • Pregnancy testing should be repeated three weeks after commencing a new contraceptive method even if the first test was negative to detect an early pregnancy that may not have been picked up after unprotected sexual intercourse in the preceding three weeks
  • Failure rates of modern contraceptive methods during typical use; risk of user error is greater for contraceptive methods that are used daily compared to long-acting reversible contraception. Barrier methods are associated with the highest risk
  • The contraceptive method used is down to individual patient choice, the Faculty of Sexual and Reproductive Health (FSRH) has produced guidance on “Contraception for women using known teratogenic drugs or drugs with potential teratogenic effects”; the frequency of pregnancy testing required is based on the duration of action and typical-use failure rate of the chosen contraceptive methods

The NPA has produced a suite of patient safety resources to raise awareness of risks of use of teratogenic medicines, such as valproate containing medicines, in pregnancy.

For further information on this or any other query, please contact the NPA Pharmacy Services team on 01727 891 800 or email

Produced by the NPA Pharmacy Services team March 2019.