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BACKGROUND: Toxicology studies have shown adverse effects of developmental exposure to industrial phenols. Evaluation in humans is challenged by potentially marked within-subject variability of phenol biomarkers in pregnant women, which is poorly characterized.

OBJECTIVES: We aimed to characterize within-day, between-day, and between-week variability of phenol urinary biomarker concentrations during pregnancy.

METHODS: In eight French pregnant women, we collected all urine voids over a 1-wk period (average, 60 samples per week per woman) at three occasions (15 +/- 2, 24 +/- 2, and 32 +/- 1 gestational weeks) in 2012-2013. Aliquots of each day and of the whole week were pooled within-subject. We assayed concentrations of 10 phenols in these pools, and, for two women, in all spot (unpooled) samples collected during a 1-wk period. We characterized variability using intraclass correlation coefficients (ICCs) with spot samples (within-day variability), daily pools (between-day variability), and weekly pools (between-week variability).

RESULTS: For most biomarkers, the within-day variability was high (ICCs between 0.03 and 0.50). The between-day variability, based on samples pooled within each day, was much lower, with ICCs>0.60 except for bisphenol S (0.14, 95% confidence interval [CI]: 0.00, 0.39). The between-week variability differed between compounds, with triclosan and bisphenol S having the lowest ICCs (<0.3) and 2,5-dichlorophenol the highest (ICC>0.9).

CONCLUSION: During pregnancy, phenol biomarkers showed a strong within-day variability, while the variability between days of a given week was more limited. One biospecimen is not enough to efficiently characterize exposure; collecting biospecimens during a single week may be enough to represent well the whole pregnancy exposure for some but not all phenols.