['Our objective was to compare the effect of two pain relief methods (remifentanil vs. nitrous oxide) on the success rate of external cephalic version.', 'We conducted a randomized open label parallel-group controlled single-center clinical trial with sequential design, at Cruces University Hospital, Spain. Singleton pregnancies in noncephalic presentation at term that were referred for external cephalic version were assigned according to a balanced (1:1) restricted randomization scheme to analgesic treatment with remifentanil or nitrous oxide during the procedure. The primary endpoint was external cephalic version success rate. Secondary endpoints were adverse event rate, degree of pain, cesarean rate and perinatal outcomes.', 'The trial was stopped early after the second interim analysis due to a very low likelihood of finding substantial differences in efficacy (futility). The external cephalic version success rate was the same in the two arms (31/60, 51.7%) with 120 women recruited, 60 in each arm. The mean pain score was significantly lower in the remifentanil group (3.2 ± 2.4 vs. 6.0 ± 2.3; p < 0.01). No differences were found in external cephalic version-related complications. There was a trend toward a higher frequency of adverse effects in the remifentanil group (18.3% vs. 6.7%, p = 0.10), with a significantly higher incidence rate (21.7 events/100 women vs. 6.7 events/100 women with nitrous oxide, p = 0.03). All reported adverse events were mild and reversible.'] Does increased pain relief with remifentanil improve the success rate of external cephalic version : a randomized controlled trial?