Buprenorphine is emerging as the preferred pharmacologic treatment for opioid use disorder during pregnancy. We examined the relative plasma clearance of buprenorphine (BUP) across pregnancy. Pregnant women with opioid use disorder participating in a prospective, observational study from 2013 to 2016 on stress in pregnancy who were receiving BUP for opioid use disorder were included. Women with an active eating disorder or suicidal ideation were excluded. Research visits occurred at 4-6-week intervals across pregnancy and the early postpartum period and included medication exposure history and blood samples. All assays for BUP serum concentrations at steady state were completed. Relative weight-adjusted clearance (Cl) was calculated using Cl = (daily dose [mg]/ body weight [kg])/serum concentration [ng/ml]. We collected 112 maternal blood samples from 29 women throughout pregnancy and the postpartum period. Serum concentrations for BUP ranged from < 0.2 to 15.8 ng/ml. Eleven women, with greater than three collected samples, increased their daily dose of BUP during pregnancy; however, there were no significant differences in relative clearance of BUP across this same period. This data suggests that women with opioid use disorder receiving BUP did not demonstrate a significant increase in BUP clearance across pregnancy despite increase in dosages during pregnancy. When selecting an appropriate BUP dosage for management of perinatal opioid use disorder, gestational stage appears not to be an important covariate and should be based on an individualized approach.