Environmental and Occupational Factors on Implantation Failure

Introduction

Although the focus of this chapter is on the success of in vitro fertilization (IVF) after exposure to hazardous substances in the workplace, the outcome of any attempt to attain a live birth depends on several factors, primarily the union of putatively normal sperm with oocytes. From 1979 to 2004, the Medline and PubMed databases are searched for papers that link IVF achievements and infertility to occupational exposure to hazardous substances. There is, however, a lack of data which links human exposure to hazardous substances and IVF success. Hence, in relation to reproductive outcomes, we will address the available exposure data and explain their importance to IVF.

Infertility has frequently been described as failure to attain pregnancy within one year of unprotected intercourse. Delays in the time needed to become pregnant or pregnancy loss before term is regarded as proof of subfertility. The understanding of better infertility prevalence along with rising knowledge of the toxicity of environmental contaminants to reproductive function in wildlife and laboratory animals has resulted in increased research focus on infertility aetiology. The physical environment, behavioral and socioeconomic factors, as well as environmental pollutants are among the factors thought to influence human fertility. Schull (1984) stated that the evidence as to whether adverse conditions at the workplace present a risk to human fertility is not conclusive. Nine years later, Baranski (1993) examined the then recent literature on the adverse effects of occupational influences on fertility and related reproductive outcomes, and concluded that the current findings are not adequate to support the hypothesis of female infertility triggered by occupational exposure. Lindbohm (1999) indicated that psychological stress at work is becoming a significant infertility cause. Work in this field is still considered young, though (Bonde, 1999).McElgunn (1998) claimed that critical periods prior to conception and during pregnancy are significant periods of adverse impact on fertility and the outcome of pregnancy, and that ambient tobacco smoke and exposures from video display terminals (VDT) and indoor air quality are the most common concerns of women at their workplaces. Any of these environmental conditions may have an effect on IVF tests.

In addition to physical and psychosocial factors thought to have an impact on human reproductive capacity and fertility, there is concern that the exposure to chemical pollutants has adversely affected human fertility. The impulse for enlightening the causal link between chemicals released in the atmosphere and human health came from Silent Spring, a book by Carson (1962). She suggested that there is a correlation between changes observed in wildlife ecology and human cancers and suggested that these results are the consequences of releasing countless chemicals into the atmosphere through industrial processes and agricultural processes.It took two more decades before Colborn advanced the now generally accepted environmental endocrine hypothesis (Colborn, 1991, 1995; Colborn et al., 1993, Colborn et al., 1996). The theory suggests that environmental endocrine-disrupting toxins have greater control over the production of exposed adult offspring than the genes inherited by the child, or the training they undergo.

Endocrine disrupting chemicals (EDCs) are synthetic and naturally occurring chemicals that cannot be labeled with any particular physical or chemical properties but are distinguished by their ability to replicate the effects of endogenous hormones.These features of EDC have caused concern that exposure to such compounds could be associated with adverse effects on human health (Damstra et al., 2002). Endocrine disrupters have deleterious effects in wildlife and fish species (Damstra et al., 2002), but there is no strong evidence of adverse health effects in humans. To date, epidemiological studies have failed to support a correlation between exposure to endocrine disrupters and infertility, or decreased fecundity (Foster and Holloway, 2003).However, quantification of endocrine toxicants in human ovarian follicular fluid and their association with IVF outcomes (Younglai et al., 2002), together with reported adverse effects in animals and in vitro studies (Gray et al., 2001), support concerns that exposure to endocrine toxicants may adversely affect the functioning of human ovaries.