To see if a 12-mL paracervical block works as well as a 20-mL block in decreasing discomfort after osmotic dilator insertion. The study assigned patients having osmotic dilator insertion prior to second-trimester abortion to either a 12-mL or a 20-mL 1 percent lidocaine paracervical block in this single-blind noninferiority study. The primary result was discomfort soon after osmotic dilators were inserted. Pain with paracervical block administration, total pain, and side effects were prespecified secondary objectives, with 88 individuals necessary for a noninferiority margin of 15 mm on a 100-mm visual analogue scale assuming a standard deviation of 28. Multivariable regression was used in the secondary analysis to investigate possible confounders. Between January 2018 and October 2020, 174 suitable people were reached and 96 were randomised; 91 were available for analysis. The demographics of the groups were comparable, with a mean gestation of 21 weeks and four osmotic dilators implanted. The 12-mL paracervical block was not inferior to the 20mL paracervical block for pain after osmotic dilator insertion, with a mean difference of 1.36 favouring the 12mL. After dilator insertion, the median pain ratings were 47 mm and 50 mm in 12-mL and 20-mL paracervical blocks, respectively. There was no change in median pain at baseline, after paracervical block administration, postprocedure, or total pain or discomfort. At least one lidocaine-related adverse effect occurred in 4% of individuals in the 12-mL group vs 13% in the 20-mL group, with metallic taste, ringing in the ears, and lightheadedness being the most prevalent. For pain relief after osmotic dilator insertion, a 12-mL paracervical block is noninferior to a 20-mL block.