Many environmental factors have been shown to be associated with variation in human sex ratio at birth. There are several studies that have shown the association between fathers’ occupation and offspring sex ratio.¹

Studies considering debate on the adverse effect on health of electromagnetic field have yielded variable results in animals and humans. There are a few studies that have shown a change of offspring sex ratio because of parental exposure to electromagnetic field,^2,3 but others have not.^4,5 However, there is only one study on humans.² Therefore this study was undertaken.

Using a simple questionnaire, the number of sons and daughters of 51 power linesman in Shiraz (Fars province, south of Iran) was recorded. The mean of measured magnetic field in their work place was 0.15 mT. Within these families 110 offspring (61 males, 49 females) were identified. The mean duration of employment of subjects was 19 years (range 7–29 years). Because it is reported that paternal age and birth order have some effect on offspring sex ratio, for each exposed worker, three unexposed persons from the general population of Shiraz (without occupational exposure to electromagnetic fields) were matched by age (±2 years) and number of children as a control group. In the control group, 330 offspring (168 males, 162 females) were identified. The sex ratio expressed as the proportion of the total live births that were male (male proportion). The offspring sex ratio at birth in exposed and unexposed groups were 0.555 and 0.509, respectively. Statistical analysis showed that there was no significant difference between the study groups for male proportion at birth (χ² = 0.68; df = 1; p = 0.409).

Irgens et al reported that the male proportion in offspring of men in industries with electromagnetic field was slightly reduced.² Also Wang and his coworkers reported that the sex ratio significantly decreased after mice were irradiated by an electromagnetic pulse.³ However, our data are not consistent with these reports. These data and the other two reports on experimental animals^4,5 do not support the hypothesis that exposure to electromagnetic field is an important factor for change in offspring sex ratio.