Study says environmental contaminants have increased the birth weight and frequency of genital malformations in male newborns (e.g., un-descended testes) and also decreased the male fertility.
The scientists behind this study say that the growing presence of contaminants in the environment leads to reduced male hormone action, which in turn causes the above problems.
Scientists already know that the birth weight of males is higher than that of females due to the action of male hormones on the male foetus.
Thus if there is an increase in the exposure of pregnant women to environmental contaminants that diminish the action of male hormones, there would be a decrease in the sex difference in birth weight.
The new study, in which the investigators analyzed the Public Health Agency of Canada's database on the birth weights of more than five million children born in Canada between 1981 and 2003, has demonstrated the same thing.
The researchers used statistical methods that control for changes over time of mother's age and parity, and effectively showed a sustained decrease in birth weight differences between boys and girls.
This supports the hypothesis of growing endocrine disruption related to environmental contaminants.
Contaminants found in plastic materials represent plausible candidates, since they are known to diminish the action of male hormones.
"Our study underlines the importance of probing the impact of environmental contaminants on the health of mothers and foetuses and on the reproductive potential of future generations," said lead researcher Dr. Guy Van Vliet.
The study will be published in an upcoming issue of Epidemiology.