Can environmental or occupational hazards alter the sex ratio at birth? A systematic review

Abstract

More than 100 studies have examined whether environmental or occupational exposures of parents affect the sex ratio of their offspring at birth. For this review, we searched Medline and Web of Science using the terms ‘sex ratio at birth’ and ‘sex ratio and exposure’ for all dates, and reviewed bibliographies of relevant studies to find additional articles. This review focuses on exposures that have been the subject of at least four studies including polychlorinated biphenyls (PCBs), dioxins, pesticides, lead and other metals, radiation, boron, and g-forces. For paternal exposures, only dioxins and PCBs were consistently associated with sex ratios higher or lower than the expected 1.06. Dioxins were associated with a decreased proportion of male births, whereas PCBs were associated with an increased proportion of male births. There was limited evidence for a decrease in the proportion of male births after paternal exposure to DBCP, lead, methylmercury, non-ionizing radiation, ionizing radiation treatment for childhood cancer, boron, or g-forces. Few studies have found higher or lower sex ratios associated with maternal exposures. Studies in humans and animals have found a reduction in the number of male births associated with lower male fertility, but the mechanism by which environmental hazards might change the sex ratio has not yet been established.

Paternal exposure to low-dose lead acetate: effect on implantation rate,pregnancy outcome, and sex ratio in mice

“…Contrary to our results, some studies on humans show no effect on the sex ratio (29,30). The alteration in the sex ratio due to fathers exposed to toxicant agents could be explained by endocrine disruption, and epigenetic and gene-environment interaction (25,27,31).…”

“…For a long time the ratio of male to female offspring at birth has been a simple method for monitoring the reproductive health of a population (24). Despite this, the extensive literature on the adverse effects of lead on reproductive health and birth outcomes scarcely contains studies investigating the effect of exposure on the sex ratio (25). In humans, there is increasing evidence that the birth sex ratio is altered in areas close to industry where there is increased exposure to environmental and industrial chemicals (26).…”

Follow-up of the air pollution and the human male-to-female ratio analysis in São Paulo, Brazil: a times series study

“…Secondary sex ratio (SSR) (number of male births in relation to total births) seems to be affected in population living in polluted environments and occupationally exposed to certain chemicals 9 – 13. Although the causality between environmental exposures and declines in SSR are still controversial, some authors suggest that the SSR as a sentinel indicator of reproductive injury and avoidable health exposures,14 due to environmental pollution.…”

Offspring sex ratio of Iranian dentists

“…It was also Moreover, other environmental factors, ones not considered here, may impact these dentists' children's sex ratios. The great number of studies evaluating the association of parents' job and offspring sex ratio include a wide range of occupations [1], reflecting the importance of the effect of job conditions on gender of professionals' children. On the other hand, comparison between offspring sex ratio among these various structurally different professions is difficult.…”

“…These include exposure to hazardous chemicals, ionizing and non-ionizing radiation, g-force, demographic factors, various sources of stress, and parental occupation [1][2][3]. Studies on offspring sex ratio in occupations like pilots and astronauts, radiologists, physiotherapists, orthopedic surgeons, and other jobs inquire into the relation between sex ratio and occupation and may result in an improved understanding of probable pathophysiologic explanations [4].…”