Fertility/Infertility

Sex and Gender-based Analysis of this topic

Definition
The exploration of fertility/infertility from an environmental health perspective requires looking beyond commonly-used definitions and associated measures, such as birth rate and fertility rate. See the Infertility/Fertility post for more general information on this topic. More relevant in this context is the infertility rate, which looks at the number of women attempting to conceive who are unable to become pregnant [1]. 

Known causes of infertility include sexually transmitted diseases, pelvic inflammatory disease, smoking and drug use, exposure to chemicals in the environment, occupational exposure to chemicals and radiation, and the widespread presence of artificial hormones in the environment [2]. Couples with a high presence of polychlorinated biphenyls (PCBs) in their system experienced delays in conception compared to couples with a lower presence of chemicals in their system [3].

Delayed childbearing age can also have an impact. In many cases, a specific cause cannot be attributed. There are presently no reliable estimates of the number of cases of infertility caused by environmental factors. See also Endocrine Disruption.
 
 
Sex Issues
Canadian demographic data on sex ratio indicate that, on average, there are 105 male births for every 100 female births. Investigators have found evidence of a declining sex ratio in several populations [4-5]. As numerous studies in Europe, the U.S. and Canada show, increasing numbers of feminized and intersex fish are now found in chemically contaminated waters, providing an indication that these same chemicals in the air we breathe, in the food and water we ingest, and in the products with which we come into contact may be the cause of the declining number of male births in some communities [6-10].

There is also a growing body of evidence indicating a negative environmental impact in human males, leading to decreased sperm counts and compromised sperm quality [11-12]. 
 
 
Gender Issues
There are a number of environmental toxins to which both men and women are exposed. However, women have greater exposure to various reproductive toxins, such as pharmaceutical and personal care products (including skin creams and lotions, cosmetics, hair dyes, and perfumes). Many of these products contain phthalates, a class of chemicals known to affect fertility [13-14]. Women are more likely to be in contact with toxic cleaning products on a regular basis. And women predominate in some occupations where there are known occupational hazards. One recently documented example is cash register clerks, predominantly women, who handle cash register tapes coated with products containing bisphenol-A [15]. Reproductive (i.e., endocrine-disrupting) health effects of bisphenol-A have been demonstrated in mammals and are postulated to have similar effects in humans [16-17]. 
 
 
Diversity
Some researchers have documented differences by ethnicity when measuring changes in sex ratio and other effects on fetal development. [4, 18]. It is not clear, however, whether the differences observed are related to environmental factors, cultural practices, or access to pre-natal care, for example. However, ongoing research in the Aamjiwnaang First Nation community near Sarnia, Ontario points very strongly to an environmental impact on sex ratio in a specific community as there are several large petrochemical, polymer, and chemical industrial plants immediately adjacent to this community [5].
 
 
Critique
There is clear evidence from numerous animal studies that compromised environmental health affects fertility. The effect has been demonstrated not only on usual fertility measures such as ability to conceive, time to pregnancy, and live birth, but also with respect to impact on fetal development, sex ratio, and reproductive health of subsequent generations [1, 19]. 

There is far less conclusive evidence of environmental impact on reproductive health from human studies due to the relatively small number of studies and small sample sizes. Most researchers in this field point to a need for more research. The need for a multi-disciplinary approach and improved communication has been highlighted [19]. Future study should address multi-generational fertility impacts; the effect of exposure to multiple environmental toxins in combination rather than a chemical by chemical approach; the impact of generalized air pollution and occupational exposures; and the timing of exposure, in terms of developmental stage, both in-utero and after [1, 19]. Given the complexity of this field and the enormity of what is at stake, more weight should be given to evidence of risk, rather than conclusive proof.
 
 
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