Environmental Impacts on Reproductive Health – Putting Risk in Perspective

(Published January 2010)

This chapter focuses on how providers can help patients to keep environmental risks in perspective.

Although patients can take many steps to mitigate toxic exposures and potentially increase the odds of a successful pregnancy outcome and overall reproductive health, the elimination of all hazardous environment exposures is an unrealistic goal. It is most important to make changes that reduce or eliminate significant, known reproductive hazards (e.g., smoking cessation to avoid known adverse pregnancy outcomes, elimination of known reproductive toxicants in the workplace) rather than try for complete elimination of exposure to all potential hazards. Patients need a balanced perspective on the reproductive health risks of environmental exposures. Their perspective should be informed as much as possible by empirical data, while recognizing that many potential toxicants have not undergone sufficient safety testing to generate reliable data. Health care providers can help patients achieve this balanced perspective.

Population Versus Individual Risk

Clinicians work with individual patients, not whole populations. One of the challenges of clinical care is translating data on effects seen in a population into information on real-life risks for an individual patient. Providers should remember— and convey to patients—that the elevated risks identified in population-wide studies may represent a small risk to an individual and depend on multiple factors that influence that person’s vulnerability to the effect. It is important to remember that a rare event will remain rare for an individual, even if the risk doubles or triples. For example, if a chemical increases the risk of a particular health outcome from 1 in 100,000 to 3 in 100,000, it remains a small risk overall.

However, even a modest increase in risk can translate into a sizable public health concern if the exposed population is large enough. In addition, a large increase in the populationwide risk has important implications for individuals, even if the number of exposed individuals is not high. Figure 6 illustrates how a small shift in the distribution of an attribute in a population (in this case IQ) can affect a large number of individuals. The effect of low levels of lead exposure on IQ is relatively small for an individual with an IQ score near the average, which is 100. However, this small shift has a dramatic effect at the low and high ends of the distribution curve, which are referred to as the “tails.”

In the graph, the area under the left tail represents the proportion of the population with an IQ of less than 70, which is the level used to define significant intellectual impairment or mental retardation. When the average IQ in the population is 100, there are about 6 million people who meet the criteria for severe intellectual impairment. If the average IQ were shifted to 95, there would be a significant increase in the number of intellectually impaired individuals. Tragically, this shift to the left could mean the difference between a person’s ability to live independently and being unable to manage his or her own care. Thus, population-based shifts in IQ of just a few points—due to low-level lead exposure, for example—have real effects in the middle of the distribution curve but dramatic effects on the number of individuals at the low and high ends of the distribution. If the distribution curves for testosterone level, sperm count, or thyroid hormone level were similarly shifted due to an environmental exposure, the clinical significance also could be similar.

The Relative Impact of Various Factors on Reproductive Outcomes

Providers can help patients put environmental risks in perspective by helping them take a balanced approach to risk prevention. For example, a pregnant woman should understand that changes such as smoking cessation and avoidance of reproductive toxicants at work are both important steps for reducing reproductive risks.

Clinicians can support patients by providing comprehensive guidance to all women of reproductive age. Topics should include nutrition, physical activity, family planning, chronic health problems, intimate partner violence, substance abuse, smoking, mental health, and access to care, as well as avoidance of harmful environmental exposures. Armed with this information, patients can focus on setting priorities for changes to increase the likelihood of positive reproductive health outcomes.

The next chapters cover some exposures that are salient for front-line providers of women’s health services: pesticides, methylmercury, chemical exposures in the workplace, and plastics-related chemicals, such as bisphenol A.

References:

1. Weiss B. Endocrine disruptors and sexually dimorphic behaviors: a question of heads and tails. Neurotoxicology. 1997;18:581–6.