Interpretation
A systematic review comparing forceps with ventouse delivery demonstrated that forceps were less likely to fail than ventouse (OR 0.65, 95%CI 0.45-0.94), but forceps carried an increased risk of maternal perineal trauma and there was a risk of neonatal injury with the use of both instruments (facial injury for forceps, and cephalohaematoma for ventouse) 18. This review did not differentiate between rotational or direct forceps, and data was insufficient to control for key confounding factors such as differences in fetal position or station. Additionally, no trials currently exist comparing primary emergency full dilatation Caesarean section with instrumental delivery 19.
The method of delivery and choice of instrument is a complex decision which represents a key dilemma for any obstetrician20. There is a multiplicity of factors to consider including the exact position and station of the fetal head, the adequacy of the female pelvis, the technique and experience of the operator and the wishes of the mother 21; and the operator must ensure the highest likelihood of successful delivery that will minimise risk for both mother and fetus 6.
We aimed to investigate factors predisposing to successful or safe delivery for delivery suite trials using regression analysis. Due to a broad selection of confounding variables, we were unable to produce a highly predictive model. Despite this, there were trends that can be highlighted from the data: in the presence of experienced operators both Keilland’s forceps and manual rotation plus direct forceps deliveries were associated with a high rate of completion with no increase in maternal or neonatal exposure to adverse perinatal outcome. Direct forceps without rotation also had a high rate of completed delivery, however this group had a very high proportion (74%) of babies in occipito-anterior position and examination of the use of direct forceps in babies with an occipito-posterior position demonstrated much lower rates of completion and high rates of adverse outcome, particularly maternal 3rd degree tear. Ventouse deliveries were associated with the lowest completion rates (75%) and the highest rates of composite risk outcome (29%), including high rates of 3rd degree tear and high rates of neonatal admission to NNU. These rates are higher than those published in systematic review19 , perhaps due to the ‘intention to deliver’ analysis used in this study. It is notable from our data that 44% of ventouse cases required the use of second instrument (usually direct forceps) and therefore, in some cases, a woman undergoing attempted ventouse delivery will have been exposed to a risk of the original ventouse delivery, a risk of sequential instrument use and a further risk of full dilatation Caesarean section.
Success or failure of any delivery attempt cannot be known a priori, and therefore it is important for more studies to help guide clinicians in clarifying the likelihood of successful delivery from the different methods available, whilst minimising maternal and neonatal risks22. This is particularly important for delivery trials performed in obstetric theatre as this is a situation that has already been categorised by an operative decision maker as a potentially more challenging delivery.

Conclusion:

This study adds to existing literature by investigating all types of delivery mode available to an operator for full dilatation deliveries in obstetric theatre and providing a comparison, adjusted for confounding factors, of both the likelihood of success and the immediate risk of such ‘trials’ to both mothers and babies. The data presented further supports the notion that attempting instrumental delivery in delivery suite theatre, as an alternative to primary emergency Caesarean section, is both reasonable and safe. In this study, ventouse delivery was less likely to achieve vaginal delivery than other methods of instrumental, potentially exposing patients in some cases to the risks of more than one form of delivery. There remains an urgent need for further research to examine in detail the factors associated with likely completion of instrumental delivery to allow obstetricians and women to make careful informed decisions regarding a safe and successful delivery trial.