A prospective randomised controlled trial of the Kiwi Omnicup versus conventional ventouse cups for vacuum-assisted vaginal delivery



The article by Groom et al.1 appearing in your journal of February 2006 is likely to have a profound effect on the future of instrumental delivery. The authors must be congratulated on the study design and for attempting to take into account all the factors that can affect the outcome of vacuum-assisted delivery.

The study shows an unacceptably high failure rate of 30.1% for the Kiwi Omnicup. This is in sharp contrast to the figure of 2% quoted by its developer, Aldo Vacca, in an observational evaluation study.2

In the past 7 weeks we have had Vacca working in our unit, giving intensive one-to-one tuition to our obstetric staff on ventouse delivery. This has been performed with the help of simulated extractions on a mannequin, computer-assisted teaching, hands-on instructions during deliveries and by his demonstrating the method on patients.

Our experience with the Omnicup during this time has been different from that reported by the authors, our failure rate being 8.2% (Six failures in 73 deliveries). Fifty-nine (80.8%) of these were performed by trainees.

The failure rate for the Omnicup that we have observed makes it worthwhile re-examining the rates reported by the authors.

They report a total of 192 attempted deliveries using a conventional cup with 38 failures, a rate of 19.8%. This may be more representative of this group than the 12.5% claimed by the authors in their subanalysis.

The single most important factor that determines the success of ventouse delivery is the correct application of the cup over the ‘flexion point’. The authors have attempted to verify this but failed to describe the method they used to delineate the flexion point and how much deviation from this point they allowed for a ‘correct’ application.

Assessment of cup placement need not have been subjective as mentioned by the authors. The flexion point is located 3 cm in front of the posterior fontanelle.3 Further, the data relating to application would have been more valid if they were determined by independent observers.

Despite my perceived competence in ventouse delivery, having performed them for more than two decades, I have now come to realise that in posterior and lateral positions of the vertex, correct application involves positioning the cup more posteriorly than is commonly performed. This can only be achieved by gently elevating the fetal scalp to manoeuvre the cup into position. This is an aspect that is difficult to learn by verbal instruction but rather more easily achieved by direct tutoring and by carefully checking the correctness of application after each ventouse delivery that one does.

Since ventouse delivery is mistakenly considered to be simple and its safety profile is assumed to be good, most trainees receive only rudimentary instructions on the method. It would thus become possible for an operator to develop an incorrect technique, which would then persist and continue throughout his or her career.

Perhaps, some of the failures described in this study were due to the reasons described above.