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PL04.2 Sex Hormones, HIV Infection and Unintended Pregnancy: Ever Since Adam and Eve
  1. W Cates
  1. FHI 360, Research Triangle Park, NC, United States


Regardless of the Genesis interpretation, human sexual behaviour is necessary for species survival. Biologically, steroidal sex hormones affect sexual function, reproductive capacity, and possibly infection risk. Women have 2 main sex hormones - oestrogen and progestin. These hormones function in two ways - endogenously to regulate the reproductive cycle and exogenously to control fertility.

In the highest HIV prevalence regions, women wishing not to conceive have limited contraceptive choices - typically injectable progestins, oral oestrogen/progestin combinations or male condoms. None of these are in the top tier of contraceptive effectiveness.

For nearly a quarter century, the hypothesis that women using hormonal contraceptives may be at increased risk of HIV acquisition has persevered. However, the results across multiple human studies have been mixed - some demonstrate increased HIV risk, but others do not. The strongest evidence that use of hormonal contraception may increase HIV susceptibility is for injectable progestin-only contraceptives. Observational studies have estimated that this method may increase HIV acquisition risk 1.4–2-fold. Their limitations include few endpoints, measurement error in contraceptive use, and likely confounding by behavioural factors. Evidence on HIV acquisition risk is weaker for oral contraceptives, and few data are available for other hormonal formulations including progestin implants or IUDs.

In addition, trade offs between the alleged risks of hormonal contraception and those of an unintended pregnancy must be considered. Four mathematical models have addressed this question. Using different assumptions, analytic algorithms and levels of rigour, they all reached similar conclusions. Withdrawal of injectable progestins has adverse pregnancy consequences, switching to implants/IUDs has better outcomes than injectables, while switching to orals/condoms was worse. While the current situation creates a public health conundrum, it also presents an opportunity to expand contraceptive choice, and concomitant reproductive rights, for women exposed to HIV.

  • HIV Acquisition
  • Sex hormones
  • Unintended Pregnancy

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