**2.4. Environmental effects of fertility**

Environment represents the totality of physical, chemical, biological and socioeconomic factors or conditions that constitute the external milieu surrounding the human organism. Up to 10% of infertility cannot be explained medically. Female factors in infertility stem from ovulation problems, thyroid irregularities, polycystic ovarian syndrome, and fallopian tube obstruction. Geographic differences may suggest environmental exposures that need investigation. Some toxins , gases can also have an impact on a person's fertility. The basic idea was to go to places in the world where we know that people have high level of exposures to substances that are suspected to cause these effects in fertility. Exploring multicompound exposures is yet another challenge in environmental epidemiology.
