High levels of toxic polychlorinated biphenyls (PCBs), a man-made organic chemical associated with adverse health reactions in humans, in the blood may contribute to embryos failing to implant during IVF, say researchers.
A US team led by Dr John Meeker of the University of Michigan Department of Environmental Health Sciences found that failure of embryo implantation was 40 percent more likely in women with the highest exposures to PCBs than in women with the lowest exposures. 'These findings may help explain why these chemicals were associated with fertility issues in other studies', said Dr Meeker.
The team tested blood samples from 765 women during 827 IVF/ICSI cycles for 57 different PCBs including PCB-153, the most common. The range of blood levels of PCB found were similar to those in the general US population. There was no correlation between levels of PCBs and post-implantation miscarriage.
Production of new PCBs in the US was banned in 1979 but they remain present in the environment in part due to releases from industrial leaks and waste and do not readily break down in the atmosphere. PCBs accumulate in living tissue and exposure can also occur through consuming seafood. Dr Meeker noted that there is not much women can do to avoid PCBs. 'Levels of PCBs have been declining gradually over the past couple of decades, but when or if these levels reach zero isn't known', he said.
Commenting on the study, Dr George Attia, director of the division of reproductive endocrinology and infertility at the University of Miami Miller School of Medicine, said he was 'not really convinced' by the findings. 'This study did not show a cause-and-effect relationship between PCBs and these outcomes,' he said. 'We cannot say it doesn't, but neither can we say PCBs have a cause-and-effect relationship either'.
The study lacked data on PCB levels or other factors in the women's partners. The researchers also noted that this effect of PCBs may not apply to couples not using IVF.
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