Persistent pollutants slow the time to pregnancy in couples.

Dec 20, 2012

Buck Louis, GM, R Sundaram, EF Schisterman, AM Sweeney, CD Lynch, RE Gore-Langton, J Maisog, S Kim, Z Chen and DB Barr. 2012. Persistent environmental pollutants and couple fecundity: The LIFE Study. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1205301.




 
Couples exposed to high levels of certain persistent organic pollutants took about 20 percent longer to get pregnant than couples with lower exposures. This study, which followed couples from Michigan and Texas, is one of the first to show that men's chemical exposures may be more important than women's in determining fertility issues. For men, links were found between 12 chemicals and longer time to pregnancy, while for women, it was five chemicals. PCBs, organophosphate pesticides and perfluorinated compounds were associated with this effect, which could be a sign of fertility problems.
 
 
 

Context

Human and animal studies suggest a link between exposure to persistent environmental chemicals and decreased fertility. These chemicals include a number of synthetic compounds used in industrial and agricultural settings as insulators, lubricants, pesticides and fungicides.

Many of the worst are called persistent organic pollutants (POPs). Most POPs were banned from use decades ago under the worldwide Stockholm Convention. These "dirty dozen" chemicals remain in the environment because they degrade slowly, accumulate in fat tissues, and can biomagnify –  or concentrate – in the food chain.

Other types of persistent chemicals are still used in products and industrial settings. Flame retardants – known as PBDEs – slow burning of clothes, furniture, electronics and other household items. Perfluorinated compounds – commonly called PFCs – repel stains and water. Some chemicals in both groups are being voluntarily phased out because of health concerns.

People, however, continue to be exposed to these chemicals in daily life. In fact, these persistent chemicals are routinely detected in human blood, urine and even within the reproductive tract (Jirsová et al. 2010; DeFelip et al. 2004).

POPs have been associated with altered menstrual cycles, reduced ovulation, pregnancy loss and reduced follicle count, which is indicative of reduced egg supply (Nicolopoulou-Stamati and Pitsos 2001). More specifically, exposure to PFC stain repellents, PBDE flame retardants and the industrial chemicals PCBs were associated with a longer time to pregnancy in women.

However, most of these studies measured chemical exposures during pregnancy, which, by nature, exclude women who are unable to become pregnant.

Time to pregnancy is a sensitive measure of fertility and reproductive success and is a calculation of the number of menstrual cycles it takes for a couple to achieve a pregnancy. Most studies assessing male fertility have not used this measure and instead rely on semen quality and hormone levels that are only correlated to fecundity and cannot accurately measure the time to a successful pregnancy. A longer time to pregnancy can suggest sub-fertility problems (if longer than six months of trying) or infertility (if longer than 12 months).

Over the past few decades fertility rates, as indicated by declining male semen quality, are decreasing. Many scientists believe early exposure to estrogen-like chemicals is contributing to fertility decline, while others believe that lifestyle changes over the same period may have a stronger contribution.

What did they do?

Between 2005 and 2007 researchers recruited 501 couples from Michigan and Texas who were trying to conceive. The couples were followed until they became pregnant or for up to 12 months of trying, which is clinically defined as infertility. The participants were in their 20s and 30s, and were not using birth control, were not getting infertility treatments and were actively trying for a successful pregnancy.

Studies of this kind are prospective, meaning that the environmental exposures were measured early before any measure of fecundity was taken.

Blood and urine samples from the men and women were taken during the preconception period. They were analyzed for 63 organic pollutants including nine pesticides, one polybrominated biphenyl (PBB), 10 polybrominated diphenyl ethers (PBDEs), 36 polychlorinated biphenyls (PCBs), and seven perfluorochemicals (PFCs).

In addition to blood samples, the couples were asked to keep daily records on sexual activity, menstrual cycles and other factors like smoking, diet and exercise. Age, use of tobacco and other lifestyle factors were taken into account during the statistical analysis.

What did they find?

During the study, 347 couples became pregnant while 154 couples did not become pregnant or dropped out of the study.

The strongest effects on fecundity were found in the men. Twelve chemicals were associated with increased time to pregnancy in men while only five were associated in women. This shows the importance of including both members of the couple in fertility and fecundity studies.

The time to pregnancy decreased with increased PCBs, but the type of PCB congener associated with the declines was different between males and females. In men, fecundability decreased 17 - 29 percent with DDE and PCBs 138, 156, 157, 167, 170, 172 and 209. In women, there was an 18 - 21 percent reduction in fecundity with relative increasing concentrations of PCB 118,167 and 209 and the perfluorochemical PFOSAs.

Overall, measured concentrations of the pollutants were lower than those reported by the Centers for Disease Control in the U.S. population for the same time period.

The findings corroborate previous studies in which one class of persistent organic pollutants – PCBs – reduced fecundity. Many of these associated PCBs have dioxin-like properties. Dioxins are another group of persistent chemicals known to decrease fertility by affecting hormone signaling and increasing time to pregnancy.

When the models accounted for prior pregnancies, the findings still remained.

Higher exposure to a variety of persistent pollutants in both men and women is associated with a longer time to get pregnant – one measure of fertility. The pollutants studied represent a variety of chemical classes, including PCBs, perfluorinated compounds and organochlorine pesticides.

The strongest associations were found in men. This study is one of the first to show that men's chemical exposures are just as important – if not stronger – than women's in determining fertility issues.

The results are an important first step that shows the exposure to chemical pollutants in both men and women can strongly affect fecundity.

The study design used in this study is important because it looks at couples trying to get pregnant rather than assessing exposure effects after pregnancy occurs. Prospectus studies like this one can get at the "chicken and egg" – or which came first – issue. Exposure levels are known for each couple before fertility issues are found, so it is more likely that the increased chemical exposure is causally related to fecundity.

This study corroborates previous findings that PCBs reduce fecundity. The results also confirm earlier findings for a lack of association between fecundity in women and exposure to DDT and its metabolite DDE. In men, DDE was associated with decreased time to pregnancy.

Importantly, the magnitude of decreased fecundity – about 20 percent longer – reported by this study is comparable to other factors known to cause fertility problems such as male and female age, body mass index and cigarette smoking. The authors adjusted for these factors in this study, so they do not contribute here. But the findings underscore the large impact that environmental pollutants can have on time to pregnancy.

This study did not try to determine the mechanisms of how the contaminants could affect time to pregnancy.

Resources

DeFelip, E, A di Domenico, R Miniero and L Silvestroni. 2004. Polychlorobiphenyls and other organochlorine compounds in human follicular fluid. Chemosphere 54:1445 - 1449.

Jirsová, S, J Msaata, L Jech and J Zvárová. 2010. Effect of polychlorinated biphenyls (PCBs) and 1,1,1-trichloro-2,2,-bis (4-chlorophenyl)ethane (DDT) in follicular fluid on the results of in vitro fertilization-embryo transfer (IVF-ET) programs. Fertility and Sterility 93:1831 - 1836.

Nicolopoulou-Stamati, P, and MA Pitsos. 2001. The impact of endocrine disrupters on the female reproductive system. Human Reproduction Update 7:323 - 330.

http://cfpub.epa.gov/eroe/index.cfm?fuseaction=detail.viewInd&lv=list.listbyalpha&r=223967&subtop=208

 

 

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