Introduction: Replacement flame retardants (RFRs) are potential endocrine disrupting chemicals of emerging concern due to restrictions on polybrominated diphenyl ether flame retardants. Little is known about the occurrence, variability, and predictors of RFR exposure in pregnant women. Methods: For this pilot study, 59 women from Providence, RI provided up to 3 spot urine samples at 12, 28, and 35 weeks’ gestation (2014-2015). We created a urine pool per woman using 1mL from each of her samples. We measured 9 RFRs in individual and pooled samples. Among women providing ≥2 samples(93%), we used linear mixed models to calculate intraclass correlation coefficients (ICCs) to measure reproducibility. We used multivariable linear regression to assess predictors of RFRs in the pooled sample. Results: We frequently detected diphenyl phosphate (DPhP)(93%), bis(1,3-dichloro-2-propyl) phosphate (BDCPP)(91%), and bis-2-chloroethyl phosphate (BCEtP)(73%), and occasionally detected (% detected): bis(1-chloro-2-propyl) phosphate (55%), dibutyl phosphate (33%), di-p-cresylphosphate (18%), di-o-cresylphosphate (2%), dibenzyl phosphate (0%), and 2,3,4,5-tetrabromobenzoate (0%). Median (IQR) BCEtP, DPhP, and BDCPP, concentrations were: 0.31 µg/L (0.17-0.54), 0.93 µg/L (0.72-1.97), and 1.18 µg/L (0.63-2.19). We observed substantial within-person variation in DPhP (ICC=0.24) and BDCPP (ICC=0.28), and less in BCEtP (ICC=0.45). Each 1 kg/m2 increase in pre-pregnancy BMI was marginally associated with greater DPhP (4.0%; 95%CI: -0.4, 8.7), BDCPP (3.9%; 95%CI: -0.3, 8.2), and BCEtP (5.9%; 95%CI: -0.3, 12.5). Household income was inversely related to RFRs (p-trends for DPhP=0.05, BDCPP=0.07, BCEtP=0.33), and age was inversely related to BDCPP (-10.5%; 95%CI: -16.5, -4.1). Conclusions: We detected DPhP, BDCPP, BCEtP in most pregnant women in this pilot study and urinary concentrations varied considerably across pregnancy. BMI and household income were important predictors of urinary RFRs.