NIH study links male exposure to phthalates with decreased fertility

Women whose male partners have been exposed to three common environmental chemicals may have a harder time getting pregnant, according to the results of a prospective study published in Fertility & Sterility by researchers at the National Institutes of Health (NIH) and other institutions.

Time to pregnancy (TTP) was 20% longer for couples in which the males had high urinary concentrations of monomethyl phthalate, mono-butyl phthalate, and monobenzyl phthalate. The compounds are used in the manufacture of plastic to make the plastic more flexible.  Neither male nor female exposure to bisphenol A (BPA), which is used in plastics and food and drink packaging, was associated with lower pregnancy rates.

The study included 501 couples from four counties in Michigan and 12 counties in Texas. They were recruited upon discontinuing contraception to become pregnant between 2005 and 2009 as part of the Longitudinal Investigation of Fertility and the Environment (LIFE) study and were not being treated for infertility.

The couples completed interviews and anthropometric assessments and provided urine specimens, which were analyzed with high-performance liquid chromatography to measure levels of BPA and 14 phthalate metabolites. The women used daily journals to record menstruation and pregnancy test results and the couples were evaluated until a positive human-chorionic gonadotropin pregnancy test or 12 cycles without pregnancy.

Fecundability odds ratios (FORs) were used by the researchers to estimate couples’ probability of pregnancy for each cycle, based on urinary concentration of the BPA and the phthalate metabolites.  Among men with high urinary concentrations of monomethyl, mono-n-butyl, and monobenzyl phthalates, FORs were 0.80; 95% confidence interval (CI), 0.70, 0.93; 0.82, 95% CI, 0.70, 0.97; and 0.77, 95% CI, 0.65, 0.92, respectively.

In a press release issued by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the study authors noted that they could not determine precisely how the compounds might affect fertility because they looked at only TTP. “Our study shows that exposure to certain phthalates can reduce the chance of conception for otherwise healthy couples,” said the study’s first author, Germaine M. Buck Louis, PhD, director of the Division of Intramural Population Health Research at NICHD in the press release. “Many people have been exposed to these compounds, so it’s important to continue to investigate whether they have any health effects.”    

To get weekly advice for today's Ob/Gyn, subscribe to the Contemporary Ob/Gyn Special Delivery.