NIH Report: PCBs, Other Pollutants May Delay Pregnancy
Study finds delays after exposure to pesticides, industrial chemicals (Nov. 14)
Couples with high levels of polychlorinated biphenyls (PCBs) and similar environmental pollutants take longer to achieve pregnancy in comparison with other couples with lower levels of the pollutants, according to a preliminary study by researchers at the National Institutes of Health (NIH) and other institutions.
PCBs are chemicals that have been used as coolants and lubricants in electrical equipment. They are part of a category of chemicals known as persistent organochlorine pollutants and include industrial chemicals and chemical byproducts as well as pesticides. In many cases, the compounds are present in soil, water, and the food chain. The compounds are resistant to decay and may persist in the environment for decades. Some — known as persistent lipophilic organochlorine pollutants — accumulate in fatty tissues. Another type — perfluorochemicals (PFCs) — are used in clothing, furniture, adhesives, food packaging, heat-resistant non-stick cooking surfaces, and the insulation of electrical wire.
Exposure to these pollutants is known to have a number of effects on human health, but their effects on human fertility — and the likelihood of couples achieving pregnancy — have not been extensively studied.
"Our findings suggest that persistent organochlorine pollutants may play a role in pregnancy delay," said the study's lead author, Germain Buck Louis, PhD.
Louis added that individuals may limit their exposure by removing and avoiding the fat of meat and fish, and by limiting the consumption of animal products.
The new findings were published online in Environmental Health Perspectives.
To conduct the study, the researchers enrolled 501 couples in Michigan and Texas from 2005 to 2009. The couples were part of the Longitudinal Investigation of Fertility and the Environment (LIFE) study, which was conducted to examine the relationship between fertility and exposure to environmental chemicals and lifestyle. An earlier analysis from the LIFE study found that high blood levels of lead and cadmium also were linked to pregnancy delay.
The women participating in the study ranged from 18 to 44 years of age, and the men were over 18. Couples provided blood samples for the analysis of organochlorines and PFCs. The women kept journals to record their monthly menstrual cycles and the results of home pregnancy tests. The couples were followed until pregnancy or for up to 1 year of trying.
The researchers calculated the probability that a couple would achieve pregnancy by using a statistical measure called the fecundability odds ratio (FOR). This measure estimates couples’ probability of pregnancy each cycle, based on their blood concentration of the compounds. A ratio of less than 1.0 suggests a longer time to pregnancy, while a ratio of greater than 1.0 suggests a shorter time to pregnancy.
The researchers examined PCB congeners — single, unique well-defined chemical compounds in the PCB category.
The lowest FORs were seen for couples in which the women were exposed to PCB congener 167 (FOR = 0.79) and in which the men were exposed to PCB congener 138 (FOR = 0.71). For each standardized increase in the chemical concentration measured by the researchers, the odds of pregnancy declined by 18% to 21% for women exposed to PCB congeners 118, 167, and 209, and to the PFC perfluorooctane sulfonamide. Perfluorooctane sulfonamide belongs to a broad class of compounds known as perfluoroalkyls, which have been used in fire-fighting foams.
With increasing exposure, the odds of pregnancy decreased by 17% to 29% for couples in which the men were exposed to PCB congeners 138, 156, 157, 167, 170, 172, and 209, and to dichlorodiphenyldichloroethylene (DDE), which is produced when the pesticide dichlorodiphenyltrichloroethane (DDT) degrades in the environment. DDT is banned for use in the U.S., but is still used in some countries.
The investigators noted that they could not rule out the possibility that some of the delays they observed may have been due to exposure to multiple chemicals. They added that these associations would need to be confirmed by other researchers.
Source: NIH; November 14, 2012.