RESUMEN
To compare the effectiveness and complications of vacuum extraction delivery between the conventional metal cup and the silicone rubber cup. A prospective randomized clinical trial of 90 pregnant women requiring assisted vaginal delivery who met the predetermined criteria for vacuum extraction were allocated to delivery by the Malstrom metal cup (46 cases) or the silicone rubber cup (44 cases). The two groups were similar in respect of age, parity gestational age and indications for assisted vaginal delivery. The mean and median numbers of tractions and time from cup application to delivery were not significantly different between the groups. The overall success rate was higher in the metal cup (89.1%) than in the rubber cup (79.5%) but not significantly different. The silicone cup was more likely to fail in cases of occiput posterior position, excessive caput, and severe degree of molding. There were no significant differences between groups in terms of Apgar scores, birth canal injury, and maternal blood loss. Scalp injuries occurred more frequently with the metal than with the rubber cup (P = 0.006). Vacuum extraction delivery with the silicone rubber cup is associated with reduced scalp injuries but has a greater tendency to fail when the fetus presents in occiput posterior position, has excessive caput or severe degree of molding.