Impact of exposure to phenols during early pregnancy on birth weight in two Canadian cohort studies subject to measurement errors (Lay summary)

Lester F, Arbuckle TE, Peng Y, McIsaac MA. Environment International. 2018 Nov 120:231-237. doi: 10.1016/j.envint.2018.08.005.

Infants with low or high birth weight have a higher risk of developing health complications. While there are many known factors that contribute to birth weight, the role of environmental chemicals is not yet clear. For example, exposure to chemicals such as triclosan (TCS) and bisphenol A (BPA) during pregnancy could have an impact on birth weight. TCS is an anti-microbial compound that is commonly found in soap, toothpaste, mouthwash, and other personal care products. BPA is commonly found in plastics, the lining of metal cans, and dental filings. This issue is important to study because Canadians are widely exposed to these potentially harmful chemicals – 65% of Canadians have detectable levels of TCS and 95% of Canadians have detectable levels of BPA.

But these chemicals are challenging to study because they don’t stay in the body very long. They are both excreted in urine in just a few hours. This means that getting an accurate measure of these chemicals from a single urine sample (like a snapshot in time) can be difficult because there will always be some error in the measurement. Collecting multiple urine samples from each person would be better, but this is often not possible because it’s expensive and time-consuming. So, there is a need to determine how accurate a single urine sample is when trying to estimate a woman’s typical exposure to TCS and BPA during pregnancy. There is also a need to explore how inaccuracy (or error) in the measurement affects the association between these chemicals and birth weight.

This research was conducted using data from the Personal-care Products use in Pregnancy (P4) Study and the MIREC Study. In the P4 study, 68 Canadian women who were less than 20 weeks pregnant provided multiple urine samples. In the MIREC study, 1822 pregnant Canadian women provided a single urine sample. Information on birth weight was collected from participants in both studies.

The first aim of this paper was to explore the accuracy of using a single urine sample as an indicator of a woman’s typical exposure to TCS and BPA. The second aim was to explore how inaccuracy from using a single urine sample can affect the association between these chemicals and birth weight. The researchers showed that a single urine sample could be used to estimate exposure to TCS with only a small amount of error, but there was much more error when estimating BPA exposure. They then looked at the association between these chemicals and birth weight before, and after, correcting for this error. They found that higher TCS exposure was weakly associated with a lower risk of an infant being small at birth, as well as a higher risk of an infant being large at birth. This weak association still held up even after correcting for error in the measurement from a single urine sample. BPA was not associated with birth weight either before or after correcting for error.

In this group of Canadian women and their infants, higher exposure to TCS during pregnancy may be weakly associated with a larger birth weight. No association was found for exposure to BPA during pregnancy and birth weight. This work is novel because the researchers corrected for inaccuracy (or error) in the measures of TCS and BPA. It is important that future research in this area continue to refine the accuracy of measures of TCS and BPA from urine samples.