BOSTON – Men exposed to environmental phthalate compounds may have about a 20% reduction in fertility, but women exposed to similar chemicals may have an increase in fecundity, investigators reported at the conjoint meeting of the International Federation of Fertility Societies and the American Society for Reproductive Medicine.
A study of couples trying to conceive showed that for men, exposure to some phthalates – esters of phthalic acid used widely in plastics, soaps, and cosmetics – resulted in a fecundity odds ratio (FOR) ranging from 0.77 to 0.82, indicating that a longer than normal time would be required to achieve a pregnancy. In contrast, women exposed to phthalates had an FOR ranging from 1.09 to 1.20, indicating increased fertility.
The investigators found, however, no associations between exposure to bisphenol A (BPA), an estrogen-mimicking plasticizing compound, and fertility in either men or women.
Dr. Michael S. Bloom
The findings show the importance of assessing both partners when trying to determine the source of reproductive problems, said Michael S. Bloom, Ph.D., assistant professor of environmental health sciences at the University at Albany, The State University of New York.
"If the authors had just measured women, they would be thinking that phthalates enhanced fecundity, as measured by a shorter time to pregnancy; had only men been observed, they would be thinking that phthalates diminished fecundity, as measured by a longer time to pregnancy," said Dr. Bloom.
Dr. Bloom was not involved in the study, but he presented the data on behalf of Dr. Germaine Buck Louis, an epidemiologist at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, who was unable to attend due to the federal government shutdown.
Previous studies have shown that persistent environmental chemicals such as polychlorinated biphenyls (PCBs) and perfluorooctanesulfonamide (PFOSA) are associated with diminished fecundity in couples as measured by a longer time to pregnancy. Yet despite their presence in everything from baby bottles to shampoo, short-lived chemicals such as BPA and phthalates have not been widely investigated for their effects on human fertility, Dr. Bloom said.
Nonetheless, emerging evidence suggests that BPA is associated with decreased semen quality and hormonal abnormalities in men, and with ovulatory and embryo implantation problems in women. Similarly, phthalates have been associated with sperm damage and decreased sperm motility among men attending fertility clinics and in the general population, and with a threefold increase in pregnancy loss among women, he noted.
The investigators looked at a prospective cohort of 501 couples in committed relationships who were stopping contraception. The female partners ranged in age from 18 to 44 years. The authors conducted a baseline interview; conducted anthropometric assessments; collected blood and urine samples at baseline to assess environmental exposures; and asked the couples to keep a daily journal on sexual intercourse and lifestyles, the female partner’s menstruation, and pregnancy test results.
The couples were followed until they either achieved a pregnancy confirmed by a positive human chorionic gonadotropin (HCG) or had 12 reproductive cycles without a pregnancy.
In multivariate analyses controlling for age, body mass index, serum cotinine and creatinine levels, research site, and time off contraception, they found that BPA was not significantly associated with fecundity in either sex.
In contrast, mono-(3-carboxypropyl) phthalate (mCPP) was significantly associated) with an FOR of 1.20 in women, and mono-n-octyl phthalate (mOP) was associated with an FOR of 1.09.
Among men, three phthalates – monomethyl phthalate, monobutyl phthalate, and monobenzyl phthalate – were associated with respective FORs of 0.80, 0.82, and 0.77. All these associations were statistically significant.
Although the authors did not find an association between BPA and fecundity in either sex, there was a data signal that suggested a possible negative effect of BPA exposure in women, and that with a large sample size the association might be statistically significant, the investigators said.
The study was supported by the Intramural Research Program at the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Dr. Buck Louis is a senior investigator at the NICHD. Dr. Bloom reported having no relevant disclosures.