Does the use of a tocolytic agent affect the success rate of external cephalic version?

Objective: Our purpose was to study the effect of ritodrine tocolysis on the success rate of external cephalic version at ≥36 weeksʹ gestation. Study Design: This was a prospective, double-blinded, randomized study. All patients were at ≥36 weeksʹ gestation, confirmed by early ultrasonography. External cephalic version assessment included nonstress testing before and after external cephalic version and ultrasonographic evaluation of type of breech, estimated fetal weight, position of placenta and fetal spine, and amniotic fluid index. Patients were excluded if the breech was not mobile or if they had any contraindications to tocolysis or external cephalic version. After randomization 283 patients received either ritodrine (111 μg/min) or identical placebo by intravenous infusion for ≥20 minutes. Up to three attempts at external cephalic version under ultrasonographic surveillance were performed. With an α error of 0.05 and a β of 0.2, 264 patients were required to complete this study. Results: There were no differences between study groups in maternal age, body mass index, gestational age, amniotic fluid index, position of fetal spine, and placental location. Statistical analysis controlled for parity because parity had a major influence on success rates. There was a higher success rate in the group receiving ritodrine tocolysis (52% vs 42%, p=0.028). Ritodrine improved success rates in nulliparous patients (43% vs 25%, p=0.026) but not in parous subjects (66% vs 58%, p=0.385). Conclusion: Ritodrine tocolysis improves the success rate of external cephalic version performed at ≥36 weeks in nulliparous patients.