Clinical and Health Affairs
Workplace Hazards to Women’s Reproductive Health
By Heidi Roeber Rice, M.D., M.P.H., and Beth A. Baker, M.D., M.P.H.
Abstract
Women make up nearly half of Minnesota’s workforce. Thus, many women, including those of reproductive age, are exposed to workplace hazards. These hazards may be chemical—toxicants such as heavy metals, pesticides, and endocrine disruptors; physical—the result of activities or proximity to something in the environment; or biological—infectious agents. And they are of growing concern among scientists and the public. Although data on the effect of these hazards on the reproductive health of women is limited, there is evidence indicating they ought to be of concern to women and the physicians who treat them. Clinicians are encouraged to assess women for exposure to workplace hazards and to communicate with them about whether such exposure might increase their risk for problems such as infertility, miscarriage, and preterm birth. This article highlights selected job-related hazards and offers suggestions for caring for working women of reproductive age.
Between 1970 and 2000, women accounted for 60 percent of the increase in the number of employees in Minnesota’s labor force.
1 By 2005, 47.3 percent of Minnesota’s workers were women.
1 Approximately three-quarters of working women were of reproductive age.
2
A growing number of women hold jobs in industries that were once dominated by men—manufacturing, agriculture, and trades such as welding and printing. Working in such fields may expose them to chemicals and agents that can pose health risks.
Unfortunately, no reliable data are available to characterize the prevalence of workplace exposure to agents and activities that may have an effect on the reproductive health of women.3 This is so, at least in part, because of the difficulty of determining the timing and intensity of exposure and the fact that individual susceptibility to hazards varies.4 However, there is increasing evidence that some chemicals found in work settings may be reproductive or developmental toxicants. Their effect on critical periods of fetal development during pregnancy is of great concern—particularly for those who counsel patients about the level of risk to which they may be exposed. As a result, the National Institute for Occupational Safety and Health is focusing research on fertility and pregnancy abnormalities and possible connections to certain occupations.
This article describes some of the hazards to which women may be exposed in the workplace and offers recommendations to clinicians about how to advise patients who may be at risk for reproductive difficulties or for miscarriage or birth defects as a result.
Selected Occupational Exposures
The Occupational Safety and Health Act of 1970 states that employers must provide a workplace that is “free from recognized hazards.” Such hazards may not be immediately apparent. For that reason, employees need to ask about the potential for exposure that may go along with a particular job.
Workplace hazards are grouped into 3 general categories: chemical, physical, and biological (Table). Although we often associate exposure to certain chemicals as a reason for concern, being subjected to physical hazards such as heat, exertion, noise, and vibration are likely more common in work environments. The following is a description of the types of exposures primary care physicians may encounter in their patients and discussion of why they are the subject of recent scientific and public interest.
Chemical Hazards
Chemicals, both synthetic and naturally occurring, are used extensively in industry. Most workers are exposed to some types of chemical substances in their jobs. Animal studies have shown more than 1,000 workplace chemicals to affect reproductive health. However, far less is known about the effect of these substances in humans, and it is difficult to extrapolate from animal findings to humans.
Although epidemiologic and toxicology data concerning the effects of workplace toxins on women’s reproductive health are sparse, it is known that heavy metals, polychlorinated biphenyls (PCBs), pesticides, and endocrine disruptors adversely affect fertility, the outcome of a pregnancy, and child development. In addition, mercury, lead, cadmium, alkylating agents, DDT, lindane, toxaphene, and polybrominated biphenyls have been linked to ovulatory dysfunction and altered menstrual patterns.3
Exposure to toxins, particularly acute high-level exposure to heavy metals and solvents, during the first 2 weeks postconception has been associated with loss of pregnancy. Teratogenic insults, such as exposure to solvents, experienced between weeks 3 and 8 are more likely to result in intrauterine growth restriction, birth defects, neurologic deficits, or loss of the fetus.5,6 Exposure at any time during gestation to neurotoxins such as mercury, lead, and tobacco may lead to both structural and cognitive effects including developmental delays and learning difficulties.7
Lead is a known reproductive toxicant, and an increased risk of spontaneous abortion has been associated with even low levels of lead in the bloodstream.8 Although lead is no longer found in gasoline and consumer products, industrial paints still contain significant amounts. Individuals who do metal work or welding, who smelt metals from ore, or who work in ammunitions manufacturing also may be exposed to lead through inhalation or ingestion as a result of improper work practices or poor hygiene. Lead exposure may also result in impaired fertility, particularly among male workers. In addition, children born to mothers who were exposed to lead at levels previously thought to be safe during pregnancy demonstrate impaired cognitive development.9
Increased miscarriage rates have been documented among women exposed to organic solvents such as toluene, xylene, and formaldehyde, which are found in paint thinners, certain sterilizing agents, and adhesives. Women working in shoe and textile manufacturing, laboratories, and printing may have chronic low-level exposure to these agents. An increased rate of spontaneous abortion has also been documented among women who work in the pharmaceutical and health care industries preparing and administering antineoplastic medications.6
Women who work in operating rooms or dental clinics are at risk for exposure to waste anesthetic gases. Studies of female workers exposed to inhaled halogenated anesthetic gases such as halothane, isoflurane, and sevoflurane have yielded conflicting results about the effect on fertility and spontaneous abortion. Of the gases used for anesthesia, nitrous oxide appears to pose the greater risk possibly because of its properties as an asphyxiant. Epidemiological and retrospective studies have reported an excessive risk of miscarriage among female workers exposed to anesthetic gases. Rowland et al. reported a 59% decrease in the probability of conception during a given menstrual cycle among female dental workers who were exposed to unscavenged nitrous oxide versus those who were not.10
Cleaning agents such as bleach are considered to be relatively benign when used as directed for routine purposes, but chemical sterilants such as ethylene oxide and formaldehyde used for sterilization of medical devices, equipment, and supplies have been linked to spontaneous abortion among workers with intense exposure.6
Much research has focused on the dangers posed by endocrine disruptors found in pesticides and herbicides. These substances mimic, bind, or antagonize the endogenous hormones.11 Even exposure to extremely low doses can interfere with production of estrogen, testosterone, and other naturally occurring hormones.
Dioxins that are released through incineration, pesticide manufacture, and paper bleaching are an example of endocrine-disrupting agents that persist in the environment. These compounds are currently being investigated to determine their impact on human fertility. People who work in metal recycling may inhale these substances. However, most individuals are exposed to endocrine disruptors through food because they accumulate in body fat.
One pesticide that behaves like an estrogen is DDT, which was banned from agricultural use in the United States in 1972 for ecological reasons. Animal studies have shown adverse reproductive effects ranging from sterility and low birth weight associated with exposure to DDT and other banned organochlorine insecticides such chlordecone. However, epidemiological studies have not consistently demonstrated adverse associations in humans.
Researchers also are studying the anti-androgenic effects of phthalates—chemicals used in the manufacture of plasticizers and commonly found in many consumer products. Although their effect on human reproduction is unclear, phthalates have been reported to disrupt the development of the testes and cause hypospadias.12,13 Women working in facilities that manufacture synthetic materials such as plastics, cosmetics, and insect repellants may be exposed through inhalation or ingestion in the case of improper handling or hygiene. For that reason, pregnant women need to exercise caution, as a male fetus is extremely sensitive to the effects of these chemicals.
Physical Hazards
Women working in the manufacturing, agriculture, and service industries as well as those who work as firefighters or nursing assistants often must perform tasks that are physically demanding. Because of the physiological changes that take place during pregnancy, including increased stress on the musculoskeletal system, intensive job-related physical demands have been associated with an increased risk for miscarriage, especially among women who have had 2 or more spontaneous abortions.14 In addition, a growing body of research has linked heavy lifting, prolonged standing, working the night shift, and working long hours during pregnancy with impaired fetal growth and preterm delivery.15,16 Researchers have suggested several reasons for this: pooling of blood in the lower extremities when standing for prolonged periods, less blood returning to the heart because of the demands of the growing uterus, and interference with circadian rhythms, which ultimately affect hormone levels.
Women who work in manufacturing or the transportation industry, especially in airports, are frequently subjected to temperature extremes, intense vibration, and excessive noise. Such exposure also may increase physiological stress and have adverse effects on the fetus leading to low birth weight or high-frequency hearing loss.17,18
A patient’s medical risk factors may exacerbate occupational risk factors. For example, if a woman is at risk for premature cervical dilation, working a physically demanding job could place her at greater risk for preterm labor.6
Biological Hazards
Infectious agents such as parvovirus B19, rubella, CMV, toxoplasmosis, and varicella are known reproductive hazards. Women at greatest risk for becoming infected are those who work in health care settings, schools, and child care facilities. Although such infections often cause mild symptoms in adults, they may result in miscarriage, low birth weight, congenital deafness and cataracts, cardiac defects, and mental retardation.
Although taking standard precautions such as handwashing, using infection-control techniques, and having the appropriate immunizations may protect most women, those who are pregnant and working in an environment where they may be exposed to such biological hazards may wish to be reassigned to a position where they have less chance of exposure.
Clinical Guidance
The first step in assessing occupational exposure to hazardous agents and activities is to know what kind of work a patient does. Unfortunately, many medical records do not contain this information, and physicians don’t always know whether their patients are working jobs that may place them at risk, or for that matter, whether the products and processes they’re exposed to are potentially harmful. The American Academy of Family Physicians, the American Academy of Pediatrics, and the American College of Obstetricians and Gynecologists are trying to prevent job-related reproductive problems by endorsing the inclusion of an occupational history as a routine part of care for patients who are pregnant or who are likely to become pregnant.19,20
Employers in the United States are required to provide Material Safety Data Sheets (MSDS) for products to which employees are exposed. However, the documents often lack adequate information regarding the risks to reproductive health of women and/or fetal development.21 They may also be written at a reading level that exceeds that of the workers most likely to be exposed. Physicians may find managers, supervisors, industrial hygienists, or company safety personnel to be more helpful in assessing exposure to harmful agents.
When a physician identifies a patient who has been exposed to an agent or activity that may be hazardous, he or she may wish to consult an occupational medicine specialist who could recommend ways to reduce or eliminate exposure. This might include making modifications to the job or substituting products that do not contain toxins. In some instances, they may advise that a woman wear protective equipment such as a respirator while on the job. They also may recommend work modifications such as lifting restrictions or temporary reassignment of pregnant workers until after they deliver.
If a medical leave must be considered, a pregnant patient may be entitled by law to certain job protections. The Family Medical Leave Act requires employers to provide for at least 12 weeks of unpaid leave each year for eligible employees under specified circumstances, including disability as a result of pregnancy. Although an employee could not use this leave to avoid possible exposure to toxins in the workplace, she may be eligible if she is unable to perform the essential functions of her job.22
Conclusion
Evaluation of reproductive risk in the workplace presents a challenge to clinicians who must estimate the level of risk to a patient, communicate the potential for harm, and provide accurate scientific information about the consequences of exposure to chemicals, physical demands, or infectious agents.23 They also must let patients know that estimating such risk is not a precise science. They must acknowledge the scarcity of data on the effect exposure to certain substances, conditions, and activities may have on reproductive and maternal health, the qualitative nature of exposure assessment, and the fact that nonoccupational risk factors also play a role in reproductive and maternal health.24 Although considerable uncertainty remains as to the potential hazards associated with exposure to chemical and biological agents or physically demanding work, physicians need to consider risks associated with them when caring for patients who are pregnant or may become pregnant in order to help them make informed decisions with regard to their own health and that of their unborn children. MM
Heidi Roeber Rice and Beth Baker are staff physicians in the department of occupational and environmental medicine at HealthPartners.
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