Published online in Human Reproduction, the study found that women who had higher levels of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in their blood took longer to become pregnant than women with lower levels. The researchers say the biological mechanisms by which exposure to PFOS and PFOA might reduce fertility are unknown, but PFCs may interfere with hormones that are involved in reproduction.
"Our data showed that higher proportions of women reported irregular menstrual periods in the upper three quartiles of PFOA and PFOS, compared with the lowest, and so this could indicate a possible pathway," said UCLA researcher Chunyuan Fei, the study's first author.
The UCLA researchers used data from the Danish National Birth Cohort to assess whether levels of PFOS and PFOA in pregnant women's plasma were associated with a longer time to pregnancy. A total of 1,240 women were included in their analyses.
Blood samples were first taken between 4 and 14 weeks into the pregnancy so that concentrations of PFOS and PFOA could be measured. The researchers also interviewed the women at around the 12th week of pregnancy to find out whether the pregnancy was planned or not and how long it took them to become pregnant. Infertility was defined as a time to pregnancy of longer than 12 months or a situation in which infertility treatments were used to establish the pregnancy, and the results were adjusted for potential confounding factors such as age, lifestyle and socioeconomic status.
The level of PFOS in the women's plasma ranged from 6.4 nanograms per milliliter (ng/ml) to 106.7 ng/ml, and from less than 1 ng/ml to 41.5 ng/ml for PFOA.
The researchers divided the women's levels of PFOS/PFOA into four quartiles and found that, compared with women with the lowest levels of exposure, the likelihood of infertility increased by 70 to 134 percent for women in the higher three quartiles of PFOS exposure and by 60 to 154 percent for women in the higher three quartiles of PFOA exposure.
"Perfluorooctanoate and perfluorooctane sulfonate were considered to be biologically inactive, but recently, animal studies have shown that these chemicals may have a variety of toxic effects on the liver, immune system and developmental and reproductive organs," said Fei. "Very few human studies have been done, but one of our earlier studies showed that PFOA, although not PFOS, may impair the growth of babies in the womb, and another two epidemiological studies linked PFOA and PFOS to impaired fetal growth."
"As far as we know, this is the first study to assess the associations between PFOA and PFOS levels in plasma with time to pregnancy in humans," said principal investigator Jørn Olsen, chair of the department of epidemiology at the UCLA School of Public Health. "We are waiting for further studies to replicate our findings in order to discover whether the chemicals should be added to the list of risk factors for infertility."
In addition to being found in household goods, PFCs, the class of chemicals to which PFOS and PFOA belong, are used in manufacturing processes involving industrial surfactants and emulsifiers. They persist in the environment and in the body for decades.
The researchers believe that although they measured the PFOS/PFOA levels after pregnancy was established, these levels probably did not change significantly from the time before pregnancy. Men's sperm quality could also be affected by PFCs and might, therefore, contribute to the associations between PFC levels and time to pregnancy, since couples would tend to be sharing the same lifestyles and have similar exposures. However, the researchers did not have data on PFC levels in fathers.
"Studies on sperm quality and PFOA/PFOS are certainly warranted," Olsen said.