In parts I and II of this series, I discussed the basic no-nos around contraception, the reason some advocate its continuous use, and what constitutes a normal menstrual cycle. Today, I'll explain a bit about population variation in reproductive function, and how it may relate to the conversation.
Both the efficacy of hormonal contraception and its non-contraceptive benefits are reduced if women do not take their prescriptions properly, and there are many reasons women do this: poor education regarding what constitutes ‘perfect use,’ ambivalence about their choice of contraception, or dissatisfaction regarding side effects. Baerwald and colleagues found different degrees of suppressed ovulation depending on when contraceptives were started; if hormonal contraception was initiated at or before ovarian follicles had reached 10mm, suppression occurred in all cases, but became increasingly less likely as follicles increased in size (Baerwald et al. 2006). One of the methods of initiating hormonal contraceptives involves the idea of a ‘Sunday Start’ where women start taking the medication the first Sunday after their last menses, rather than on the first day of menses. The reasoning is that it is easier to keep track of pills (or patches or rings) when one starts each week on a Sunday rather than on whatever day menses happens to begin. Unfortunately, significant follicular growth can occur between menses and the start of the contraception, depending on the individual and the day menses began. This can mean a woman can think she is protected from pregnancy for that cycle, but has ovulated and thus at a much greater risk for unwanted pregnancy. If a woman stops and starts – due to difficulties obtaining her prescription, traveling, or dissatisfaction with the brand of contraceptive she chooses – she may have many ovulatory cycles, or at the least many cycles where her follicles are growing and regressing. My worry is that this could lead to polycystic ovaries or even mutations during tissue remodeling that could lead to ovarian cancer (this is a hypothesis, not an observation or statement of empirical evidence).
Other reasons a woman may not stay on hormonal contraception and thus may not have ‘perfect use’ is that her normal range of variation in endogenous hormones is different from the American norm. Women from developing countries tend to have lower circulating levels of reproductive hormones (for examples directly related to contraception, see Bentley 1996; Ellison 1990; Vitzthum et al. 2004); this means their responsiveness to the exogenous hormones of contraceptives will be different, just like with overweight American women but at the other end of the spectrum. Bentley (1996) reports significant interpopulation variation in pharmacokinetic properties of hormonal contraceptives; this means that different women have different physiological responses to hormones, even when taking the same dose. She also reviewed the literature regarding interpopulation variation in side effects experienced by women on hormonal contraception (Bentley 1996). Vitzthum and colleagues (2001) report shorter duration of menses for samples of Bolivian versus Chicago women, and significantly lower endogenous hormone concentrations in Bolivian versus Chicago women (Vitzthum et al. 2004). The penultimate paragraph of the 2004 article is the most telling:
“The present study also reaffirms the conclusion of others that hormonal contraceptive dosages designed for U.S. women and other industrialized countries may be excessively high for women in developing countries, resulting in severe side-effects leading to discontinuation and, potentially, unplanned pregnancy. We have often heard Bolivian women and health workers express concern about negative experiences with hormonal contraceptives. Contrary to arguments that noncompliance is more a matter of education than biology, these data succinctly support the reports of these women that negative sequelae of hormonal contraceptives are more than an imagined problem.”
Thus we have Bentley’s review of variation in effects on contraception, several decades of literature on population variation in ovarian function via ecology, and anecdotal evidence from the mouths of women from developing countries; put together, they tell a story about a broad spectrum of women who may respond differently to hormonal contraceptives. On Monday I'll cover whether hormonal contraceptives create any behavior or cognition changes in those who take them.
Baerwald A, Olatunbosun O, & Pierson R (2006). Effects of oral contraceptives administered at defined stages of ovarian follicular development Fertility and Sterility, 86 (1), 27-35
Bentley GR. 1996. Evidence for interpopulation variation in normal ovarian function and consequences for hormonal contraception. In: Rosetta LaM-T, C.G.N., editor. Variability in human fertility. Cambridge, UK: Cambridge University Press. p 46-65.
Ellison PT (1990). Human ovarian function and reproductive ecology: new hypotheses American Anthropologist, 94 (2), 933-952
Vitzthum VJ, Spielvogel H, Caceres E, & Miller A (2001). Vaginal bleeding patterns among rural highland Bolivian women: relationship to fecundity and fetal loss Contraception, 64, 319-325
Vitzthum VJ, Spielvogel H, & Thornburg J (2004). Interpopulational differences in progesterone levels during conception and implantation in humans Proceedings of the National Academy of Sciences, 101 (6), 1443-1448