pregnancy testing and contraception for pregnancy prevention during treatment with medicines of teratogenic (teratogen) potential

Last edited 04/2019 and last reviewed 01/2022

Pregnancy testing and contraception for pregnancy prevention during treatment with medicines of teratogenic (teratogen) potential

Some medicines are known or suspected to have the potential to increase the risk of birth defects and development disorders (teratogenic potential) when taken during pregnancy, especially during the first trimester (up to week 12 of pregnancy), when a woman may not know she is pregnant. The product information for these medicines advise that pregnancy should be avoided during treatment, with advice on the need to use contraception including, in some cases, formal pregnancy prevention programmes.

When using any medicine with teratogenic potential, a woman should be advised of the risks and encouraged to use the most effective contraceptive method taking into account her personal circumstances.

FSRH guidance with respect to contraception and teratogenic drugs suggests that (2):

• women should be made aware that no method of contraception is 100% effective
  
  
• methods of contraception which are considered 'highly effective' in this context include the long-acting reversible contraceptives (LARC) copper intrauterine device (Cu-IUD), levonorgestrel intrauterine system (LNG-IUS) and progestogen-only implant (IMP) and male and female sterilisation, all of which have a failure rate of less than 1% with typical use. (Note that women using IMP must not take any interacting drugs that could reduce contraceptive effectiveness)
  
  
• additional contraceptive precautions (e.g. condoms or a second effective contraceptive method) are not required if a Cu-IUD, LNG-IUS, IMP or male or female sterilisation is being used. However, a woman may choose to use condoms in addition to reduce risk of unintended pregnancy even further and for protection against sexually transmitted infections
  
  
• typical use failure rate of combined hormonal contraception (CHC) and the progestogen-only pill (POP) is 9%; for progestogen-only injectables including depot medroxyprogesterone acetate (DMPA) it is 6%. Given the importance of avoiding pregnancy during use of known teratogenic drugs or drugs with potential teratogenic effects, the FSRH recommends that in this situation women using CHC, POP or DMPA should be advised to use additional contraceptive precautions (e.g. condoms). (Note that women using CHC or POP must not take any interacting drugs that could reduce contraceptive effectiveness)
  
  
• use of barrier methods, withdrawal and fertility awareness methods alone is not recommended.

Risk of pregnancy should be assessed prior to each teratogen prescription (1)

• risk of pregnancy may be high at start of a method or when switching between methods due to risk of pregnancy from unprotected sex prior to starting the method, unreliable use of the previous contraceptive method, and/or time needed to establish contraceptive efficacy at the start of the new method.
• pregnancy tests at start of contraceptive method may not detect an early pregnancy following unprotected sex in the last three weeks
  
  
• any starter on new method contraception should have a repeat pregnancy test at 3 weeks if there is any risk of pregnancy at start of contraceptive method . The duration of teratogen prescriptions may need to be shortened for patients who use contraceptive methods that require frequent pregnancy testing (1)

Reference:

• MHRA (MArch 2019). Risk of pregnancy should be assessed prior to each teratogen prescription
• FSRH (February 2018). FSRH CEU Statement: Contraception for women using known teratogenic drugs or drugs with potential teratogenic effects