Young women's fertility knowledge: partial knowledge and implications for contraceptive risk-taking.

Young women would benefit from a more nuanced understanding of fertility. Episodes of UPSI that do not result in pregnancy can encourage a belief that 'it won't happen to me', and this has implications for taking chances with contraception. Partial knowledge about the effectiveness of EHC may also lead to unintended pregnancy. Calculating the number of hours following UPSI generates overreliance on what is only one of the factors determining the effectiveness of EHC. Information regarding the link between EHC and failure rates near the day of ovulation needs to be more widely publicised.