FSRH Explainer: can genetics determine whether contraception might fail for some women?

Professor Sharon Cameron, Co-Director of the Clinical Effectiveness Unit of the Faculty of Sexual and Reproductive Healthcare (FSRH), explains.

The Guardian and The Independent have reported on a new study about genetic traits that might make contraception less effective for some women.

According to Professor Sharon Cameron, Co-Director of the Clinical Effectiveness Unit of the Faculty of Sexual and Reproductive Healthcare (FSRH), genetic makeup might have an impact on how well contraception might work for some women, but this is only one study and it is very early to tell:

“This study of the progestogen only contraceptive implant suggests that there are genetically determined variations in how our bodies deal with the hormones in contraception that could be responsible for why some hormonal methods of contraception maybe be less effective in some women and why some of these methods might fail even with perfect use.

"The progestogen-only implant available for women in the UK is a highly effective method of contraception. It is a small flexible plastic rod that is placed under the skin and releases one hormone, progestogen. It has a very low failure rate – around one in a thousand women will get pregnant over three years of use. It also has health benefits such as alleviating period pain. 

"Additionally, hormonal methods can exert contraceptive action in more than one way. For instance, the implant mechanism is to prevent ovulation, but it also has effect on cervical mucus. It makes the mucus thicker, so sperm is less likely to penetrate. Therefore, even if the blood dose is less than what we 'think' might be a threshold for preventing ovulation, the implant has back up actions (at lower doses than required to prevent ovulation) that might also prevent pregnancy.

"Although genetic makeup might have an impact on how well contraception might work for some women, this is only one study and it is very early to tell whether this technology will be helpful in the future. Any clinical application of this technology, for instance, whether a genetic test would tell women if they will break down the hormones in contraception to a greater extent than other women so making it less effective for them, is still a long way from becoming reality.

"There is no need for concern as the low failure rate of the progestogen-only implant is proof that it works very well to prevent unplanned pregnancies. I would advise women to keep using the method that suits them best and, to talk to their GPs or sexual and reproductive healthcare professionals about the range of available methods."

For press queries, please contact Camila Azevedo at externalaffairsmanager@fsrh.org