The numbers used below are either from the CCDHB published figures or are conservative estimates based upon Lynley Davidson's 16 years of experience as a practicing midwife.
Approximately 1 in 100 women can be expected to have an undiagnosed breech presentation at the start of labour. Approximately one in 5 women undergoing vaginal breech birth will suffer injury to the infant during vaginal delivery of the baby. The mortality rate is at least twice as infrequent. Approximately 75% of women in labour with a breech presentation will show clinical signs (e.g. meconium) resulting from the breech presentation and a vaginal examination will be undertaken. That examination will be 75% successful in diagnosing the breech. So without any intervention approximately one in 2000 labour episodes will result in the birth of an undiagnosed breech baby that dies. It is quite a rare combination of circumstances.
A VE during a normal labour, without any clinical indications, might optimistically identify 3 out of 4 undiagnosed breech presentations as a consequence of undertaking the VE. This further improves the odds to about 1 in 8000. However even with such a diagnosis the chances of getting safely to the base hospital in time, and having any better outcome in the hospital is at best 50:50. This again reduces the odds back to 1:4000. Twice the undiagnosed 1:2000. Hence if we vaginally examine 4000 women who are labouring normally in the rural environment we stand to save from breech death one baby.
What of the other 3999 women, approximately one third of which will be first time mothers? 20% of these women, even without a VE during normal labour, will have undergone other complications of labour and transferred into the base hospital. The most common complication is a failure to progress adequately in labour. Maintaining the progress of labour is an important safety goal, particularly for midwives in the rural environment. A vaginal examination can be a stressful and logistically difficult process for some labours. More importantly however my wife and many of her midwifery colleagues have observed, because of their constant attendance during labour, that for a significant number of women the stress of the VE and the information it provides can significantly slow the progress of labour. This is particularly noticeable in first-time mothers where their inexperienced expectation of how far advanced they are through labour is deflated by the result of the VE. Such an effect would probably not be noticed by a consultant obstetrician who would rarely remain long enough with a woman subsequent to performing a VE. There follows a consequent loss of the momentum of the labour the woman previously had. This very real effect has significant safety implications for the labour.
Of the 3999 women mentioned above let us consider just the 1100 first-time mothers who would not normally have transferred to the base hospital for other reasons. Approximately 1 in 3, or 370, will have the pace of their labour significantly affected by the VE. Of these women a further 1 in 3 ( about 120) will have their progress so severely affected they will end up transferring to Wellington Hospital directly as a result of having had a VE. Of the women who transfer to Wellington Women's hospital for lack of progress 50 % normally end up having a caesarean section delivery. A caesarean section is a major operation with significant ensuing health consequences and greater risks of injury or death to mother and child than a normal vaginal delivery. So for every undiagnosed breech birth we save by routine VE we can expect to cause 60 extra caesarean section deliveries amongst first-time mothers alone. For the average normal labour the VE increases the chance of transfer to the base hospital by 10% and the chance of caesarean section by 5%. Although not yet undertaken, a comparison of the caesarean birth-rate for midwives (or obstetricians) who routinely undertake VE's during normal labour, compared with those who do not, would be expected to confirm this effect. The steadily climbing caesarean rate within New Zealand probably has as one of its sources the routine VE practice.
This is the dilemma all midwives face. Although the above numbers are a form of statistical calculation it is at the core of why many midwives will only do a vaginal examination if there is a clinical indication of a problem.