Background: Recent studies show a rapid growth among pregnant women using high potency opioids for common pain management during their pregnancy. No study has examined the duration of treatment among strong opioid users and weak opioid users during pregnancy. We aimed to investigate the prevalence of prescribed opioid use during pregnancy, in Quebec; and to compare the duration of opioid treatment between strong opioid users and weak opioid users. Methods: Using the Quebec Pregnancy Cohort (1998-2015), we included all pregnancies covered by the Quebec Public Prescription Drug Insurance Program. Opioid exposure was defined as filled at least one prescription for any opioid during pregnancy or before pregnancy but with a duration that overlapped the beginning of pregnancy. Prevalence of opioids use was calculated for all pregnancies, according to pregnancy outcome, trimester of exposure, and individual opioids. The duration of opioid use during pregnancy was analyzed according to 8 categories based on cumulative duration (< 90 days vs. ≥90 days), duration of action (short-acting vs. long-acting) and strength of the opioid (weak vs. strong). Results: Of 442,079 eligible pregnancies, 20,921 (4.7%) were exposed to opioids. Among pregnancies ending with deliveries (n = 249,234), 5.4% were exposed to opioids; the prevalence increased by 40.3% from 3.9% in 1998 to 5.5% in 2015, more specifically a significant increase in the second and third trimesters of pregnancy. Weak opioid, codeine was the most commonly dispensed opioid (70% of all dispensed opioids), followed by strong opioid, hydromorphone (11%), morphine (10%), and oxycodone (5%). The prevalence of codeine use decreased by 47% from 4.3% in 2005 to 2.3% in 2015, accompanied by an increased use of strong opioid, morphine (0.029 to 1.41%), hydromorphone (0.115 to 1.08%) and oxycodone (0.022 to 0.44%), from 1998 to 2015. The average durations of opioid exposure were significantly longer among pregnancies exposed to strong opioid as compared to weak opioid regardless of the cumulative duration or duration of action (P < 0.05). Conclusions: Given the differences in the safety profile between strong opioids and the major weak opioid codeine, the increased use of strong opioids during pregnancy with longer treatment duration raises public health concerns.