Soft versus rigid vacuum extractor cups for assisted vaginal delivery.

BACKGROUND: The original cups used for vacuum extraction delivery of the fetus were rigid metal cups. Subsequently, soft cups of flexible materials such as silicone rubber or plastic were introduced. Soft cups are thought to have a poorer success rate than metal cups. However they are also thought to be less likely to be associated with scalp trauma and less likely to injure the mother.

OBJECTIVES: The objective of this review was to assess the effects of soft versus rigid vacuum extractor cups on perineal injury, fetal scalp injury and success rate.

SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register. Date of last search: February 2000.

SELECTION CRITERIA: Acceptably controlled comparisons of soft versus rigid vacuum extractor cups.

DATA COLLECTION AND ANALYSIS: Two reviewers assessed trial quality and extracted data. Study authors were contacted for additional information.

MAIN RESULTS: Nine trials involving 1375 women were included. The trials were of average quality. Soft cups are significantly more likely to fail to achieve vaginal delivery (odds ratio 1.65, 95% confidence interval 1.19 to 2.29). However, they were associated with less scalp injury (odds ratio 0.45, 95% confidence interval 0.15 to 0.60). There was no difference between the two groups in terms of maternal injury.

REVIEWER'S CONCLUSIONS: Metal cups appear to be more suitable for 'occipito-posterior', transverse and difficult 'occipito-anterior' position deliveries. The soft cups seem to be appropriate for straightforward deliveries.