An environmental pollutant present in most humans can significantly lower the chances of a woman conceiving via in vitro fertilization, according to new research, a finding that also may extend to women trying to conceive naturally.
While the new work directly addresses the growing segment of the population conceiving via IVF, it's likely to also have implications for women trying to conceive the old-fashioned way, because PCBs may affect all conception similarly. Other studies are consistent with this possibility.
So-called PCBs are chlorinated organic chemicals that were once widely used in industry and consumer goods, often as insulating and cooling fluid in electrical transformers and capacitors. Found to have numerous health effects, they were banned in the late 1970s. PCBs have been linked to, among other things, higher cancer rates and developmental abnormalities in infants. Also, PCBs are highly resistant to degradation, so they persist in our environment.
"PCBs have been associated with a number of effects in experimental animals and human studies, many of those associated with reproduction," said study leader John Meeker of the University of Michigan School of Public health. Other studies, for example, have indicated that women with higher levels of PCBs take longer to become pregnant than women with lower levels.
The new work, published today in the journal Environmental Health Perspectives, found that the women in the top quarter of blood PCB levels had twice the odds of a failed embryo implantation as those in the quartile with lowest blood PCBs. They also had 41 percent lower odds of the in vitro ultimately resulting in the birth of a child.
A doubling of the odds of implantation failure, "is large," Meeker said. "It does suggest that while there are probably many factors involved in implantation, this particular exposure might be one of them."
However, the women in the study weren't from a population with extreme levels of PCBs, such as would be seen in Inuits, or Swedish fishermen's sisters or Taiwanese women suffering from contaminated cooking oil exposure. So, even more or less within the distribution of levels in the normal population, this effect appears.
The researchers do not know whether the slightly elevated median levels could have something to do with the women's infertility, or whether they just reflect differences in the timing of the measurements, because PCB levels in the population are declining and their measurements predate those representing the general population.
Today, most human exposure comes from contaminated food, primarily fish, but also meat and dairy sources. Like other persistent organic pollutants, they concentrate in fat in long-lived animals higher up the food chain, making certain fish particularly high in PCBs. Removing skin and fat from fish reduces their PCB content.
The new study, by looking at a population where conception is being monitored closely, could put a finer point on what stage of conception and pregnancy might be most sensitive to PCBs.
"It gives us an opportunity to study endpoints that aren't normally observable in humans," Meeker said. "In the normal population, this goes as an undetected pregnancy and could contribute to increased time to pregnancy."
"This is a very interesting paper and one that suggests select environmental chemicals may be associated with adverse reproductive outcomes including early pregnancy loss," said Germaine Buck Louis of the National Institute of Child Health and Human Development in Bethesda, Md.
"This unique study population provides important insight into the relation between hormonally active environmental chemicals such as PCBs and a spectrum of reproductive outcomes during some of the most sensitive windows of human development," she said.