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Organophosphate esters (OPEs) are a group of chemicals used as flame retardants and plasticizers that replaced polybrominated diphenyl ethers in consumer products such as furniture and electronics. To characterize exposure to OPEs during fetal development, we measured urinary OPE metabolite concentrations in women twice during pregnancy (16 and 26 weeks' gestation) and at delivery (n = 357). We also previously quantified house dust OPE parent compound concentrations at 20 weeks' gestation (n = 317). Diphenyl phosphate (DPHP) had the highest geometric mean urinary concentrations (1.5–2.3 μg/g creatinine), followed by bis(1,3-dichloro-2-propyl) phosphate (BDCIPP; 0.75–0.99 μg/g creatinine), and bis(2-chloroethyl) phosphate (BCEP; 0.72–0.97 μg/g creatinine), while dibutyl phosphate (DNBP) had the lowest concentrations (0.25–0.28 μg/g creatinine). Urinary OPE metabolites were moderately correlated with each other at 26 weeks (r s : 0.23–0.38, p < 0.001) while the correlations at 16 weeks and delivery were slightly weaker. Intra-class correlations for urinary metabolites measured at three time points were poor (0.16–0.34), indicating high variability within individuals. Dust concentrations of OPE parent compounds were associated with BCEP, BDCIPP, and DPHP concentrations in urine at some but not all time points. In linear mixed models of urinary OPE metabolite concentrations, household size was inversely associated with BCEP concentrations, and being non-white was associated with lower BDCIPP and DPHP concentrations. Urine samples collected in the summer had the highest OPE metabolite concentrations. This study highlights the need to collect multiple urine samples during pregnancy to define exposure patterns and investigate potential periods of susceptibility. • House dust is considered a major source of organophosphate ester (OPE) exposure. • We measured urinary OPE metabolites in pregnant women at three timepoints. • Intraclass correlations between measurement timepoints were poor. • Non-white race was associated with lower OPE metabolite concentrations. • House dust OPEs and household size were associated with urinary OPE metabolites. [ABSTRACT FROM AUTHOR]