10. Female exposure to phenols and phthalates and time to pregnancy: the Maternal-Infant Research on Environmental Chemicals (MIREC) Study (lay summary)

Vélez MP, Arbuckle TE, Fraser WD. Fertility and Sterility. 2015;103(4):1011-1020.e2. doi: 10.1016/j.fertnstert.2015.01.005

Exposure to environmental chemicals can potentially result in adverse health effects, including impacts on female fertility. This study, which was carried out by researchers at the University of Montreal, investigated the potential effect of women’s exposure to bisphenol A (BPA), triclosan, and phthalates on their fertility, as measured by “time to pregnancy”, i.e., how many months it took to become pregnant.

A total of 2,001 women from the MIREC Study were assessed during their first trimester of pregnancy, with 1,742 women included in the BPA analysis, 1,699 in the triclosan analysis, and 1,597 in the phthalates analysis.

This research found that the levels of BPA in first-trimester maternal urine were not significantly associated with reduced fertility as shown by a longer time to become pregnant. Triclosan exposure was associated with a longer time to pregnancy for women who had the highest urinary levels, defined as greater than 72 nanograms per millilitre (ng/mL), compared with women who had lower urinary triclosan levels. (Note: a nanogram is one-billionth of a gram). Interestingly, the results were different for phthalates: exposure to some phthalates suggested a shorter time to pregnancy, although the evidence for this effect was not considered strong.

The researchers in this study concluded that exposure to elevated levels of triclosan (greater than 72 ng/mL) may be associated with reduced fertility, i.e., a longer time to become pregnant; and that some phthalates might be associated with a shorter time to pregnancy. There was no evidence of BPA having a negative effect on the length of time it took to become pregnant.

It should be noted that this study had some important limitations: there was only one measurement of exposure available for each woman, and there can be a good deal of variability among urine samples taken from the same woman at different times due to the fact that BPA, triclosan, and phthalates are quickly eliminated in the urine. In addition, the urine samples were taken after the women had become pregnant, and not during the months when they were trying to become pregnant. Finally, there was no information available on the male’s exposure. For these reasons, further study is needed to confirm these findings.