A French invention, the cap is a suction device which is attached to the unborn baby's head in cases where labour has been prolonged and the baby shows signs of distress. When the vacuum machine is turned on, the infant, hopefully, is gently eased out of the vagina with each contraction. The cap leaves a swelling on the baby's head but this normally disappears within 24-36 hours.
The cap has long been used in Scandinavia and many other parts of the world but has only recently become popular in Britain, where forceps - two blunt blades that cup the head - have been the traditional method for assisted deliveries. According to the Royal College of Obstetricians and Gynaecologists' guidelines, ventouse should now be the "instrument of choice" for assisted deliveries because all the evidence shows that it causes less bruising, tearing and other damage to the mother.
In terms of the effects on the baby, research suggests there is little to choose between forceps and ventouse. Both methods can result in bruising, which can look shocking but is not usually serious. Both have also been associated with more serious damage, but this is rare: an estimated one in 10,000 assisted deliveries result in brain injury or death (compare this with one in 1,000 babies who die during labour). On rare occasions, the ventouse results in "devascularisation", in which blood flow is interrupted and cells die, so that a part of the scalp may actually sheer away. This used to be common when a metal cap was used, but nowadays the ventouse is made of rubber or silicone. Babies are also more likely to suffer injury when more than one instrument is used to pull them out in succession: forceps followed by ventouse, for example.
What is important in the end is not which instrument is used but who is using it - and how skilled they are. Most assisted deliveries are carried out by junior doctors, and there are fears that reductions in hours and changes in training mean they have less experience of maternity wards than their predecessors (although moves are afoot to develop a model with which junior doctors can simulate vacuum deliveries).
An error of judgement by an inexperienced doctor can result in problems: a ventouse used on a big baby, for instance, may bring out the head but result in damage to the shoulders; an emergency caesarean may have been the better choice.
One important principle with assisted delivery is that the baby must come out reasonably easily or the method abandoned and an emergency caesarean performed instead.
There is certainly no justification for a wholesale return to forceps, in this country an instrument unchanged in basic design since the nineteenth century. Although in emergencies forceps may be more effective, they can potentially cause more damage: it allows a doctor to use about 100kg of force, compared to a ventouse - which falls off if more than about 15-20kg of force is applied.
Some babies are always going to need help getting out (although there might be fewer assisted deliveries if doctors were better taught how to avoid them - by encouraging the mother to stay upright, for example). In the hands of a skilled practitioner the ventouse is safe, and complications are rarenReuse content