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Amniotomy: to do or not to do?

13 June, 2008

Amniotomy: to do or not to do?

The use of amniotomy is important under certain circumstances, but Marjorie Vincent argues that routine use of the procedure to speed up labour is not necessarily beneficial.
The use of amniotomy is important under certain circumstances, but Marjorie Vincent argues that routine use of the procedure to speed up labour is not necessarily beneficial.
 Midwives magazine: May 2005


The definition of amniotomy is the rupture of the amnion and chorionic membranes that surround the fetus, encasing it in a sac of amniotic fluid. It is performed by the use of a crotchet-like, long-handled hook passed per vaginum (commonly referred to as an amnio-hook). This article aims to challenge existing perceptions about the routine use of amniotomy.


Why is amniotomy performed?


There are a number of reasons why the procedure may be performed: _ To assess the fetal condition by checking for the presence of meconium liquor _ To introduce monitoring devices, such as a fetal scalp electrode or an intrauterine pressure gauge _ Out of the clinical assumption that it increases labour contractions and thus improves progress. However, it is necessary to address the question of whether routine amniotomy is now so common, it has become a mere tool in the midwifery kit.


Nature’s wonder


As a biologist first and foremost, I feel that there has to be some biological reason for the existence of the amniotic sac, not only in pregnancy but within labour and delivery. If spontaneous rupture of membranes does occur, then this is beyond our control, but if it does not, do we see this as something that will lead to an abnormal birthing experience? What are the biological advantages of the amniotic sac being left intact during labour and delivery? Certainly one can see that this could be likened to Mother Nature’s bubble-wrap, with the fetus being well-protected and padded within its sac. The bulging membranes at the introitus serve to pre-stretch the perineum before the head is crowned. The assumption is that labour will be slower, but is this definitely the case? If, within that sac, is a well-positioned passenger, (that is, the fetus) then the progression will be just as fast as if the membranes were not ruptured. In fact, the pressure from intact membranes could and does contribute to the ripening and dilation of the cervix. The pressure exerted will stimulate the oxytocin surges, just as the bony prominences of the presenting part would. So where do we get this idea that amniotomy will speed things up? My assessment tool served as a reminder that the progress is multifactorial (Vincent, 2003). Progress is complex and multifactorial, and depends on power, efficiency and the position of the fetus, as well as the response in the cervix.


 Common beliefs about amniotomy


The belief that amniotomy will increase contractions and thus power and progress is not always in evidence in clinical practice. Many midwives when inducing labour will have had the experience of no power or very minimal power at artificial rupture of the membranes (ARM). Experience from the labour room would strongly suggest that one intervention leads to another. There is an increased likelihood that syntocinon infusion will be necessary – this may or may not lead to increased progress. It is important to be wary of assessing the progress from cervical dilation alone, as it may well be found that the bulging membranes exert the pressure necessary to dilate the cervical os to, for example, 6cm, but on amniotomy the os shrinks to 4cm. However, at least the cervical os has demonstrated its ability to stretch to 6cm. The need for ARM in the induction process has been challenged by the Centre for Clinical Effectiveness in Monash University, Australia (Shaw and Anderson, 1999). Their findings suggest that by conserving the membranes, there was a lower rate of maternal infections, cord compression, blood transfusion and severe variable decelerations. The observation of lower rates of cord compression and severe variable decelerations suggest that the process of labour is less stressful to the fetus. The cord is protected in its bubblewrap as the uterine muscles bear down on the contents of the womb. Thus, the implication is that fewer incidences of fetal distress and emergency delivery would be seen.


Should an intervention be performed when we are in a midwifery-led arena or at a home birth? There are dangers to be experienced and findings that could alarm or panic both practitioner and mother. I believe amniotomy should only be performed in the obstetric arena where there is a team to respond to any complication that may arise. Granted, the midwife is capable of performing this, but it should only be done knowing the commitments of those around you and with the knowledge of the rest of the team. There are dangers – can you be certain there is no vasa praevia present? After all, it is a blind procedure. Therefore, there can be no certainty that you are not tapping into vessels that are part of the overall blood supply to the fetus. Admittedly, I have seen this only once in my career while assisting a private consultant, but it was only by a quick call to the crash team that we were able to save the baby with an emergency caesarean section (CS). Most midwives fear cord prolapse and an amniotomy should not be done on a case where the presenting part is high.


What if when at a home birth or in a midwifery-led unit the membranes are ruptured and meconium liquor grade two or three is found – surely this will lead to transfer to the obstetric unit? This is an indication that the fetus is in some stress and needs to be transferred, but it could easily have resulted from an incident in utero before labour started. It is possible that the presence of the membranes and amniotic fluid could have provided the necessary cushion and protection to the fetus throughout labour. If the presence of meconium is found, then it may be a danger to compromise the fetus further by rupturing the membranes and potentially causing either hypertonia and/or cord compression. This is an issue central to our practice and as yet we do not have the evidence to answer yes or no. Amniotomy constitutes active management of labour and is not without risk to the fetus. An already compromised fetus may be put at further risk by an amniotomy, as the uterus may become hyperstimulated.


 Literature review


The literature falls into two firm schools of thought regarding amniotomy. These are that it: _ Prevents dystocia, particularly in the primipara _ Can lead to dystocia, if performed early in labour. The conclusions of a study published by Fraser et al (1993) proclaimed that early amniotomy was an effective method of shortening labour and reducing dystocia in the nulliparous, but that it did not reduce the incidence of CS. The development of the partogram with action and alert lines, based on the O’Driscoll line of progression, influenced the use of amniotomy to form an action in response to an alert on slowing progress. However, there exists a counter argument, as suggested by Friedman, that amniotomy could, actually slow down labour. Thornton and Lilford (1994) looked at six trials including work performed in Canada and the UK and found that they demonstrated only a modest decrease in the duration of labour in the randomisation of ARM. Further meta-analysis failed to show any real effect on the maternal and fetal outcomes. Most of the literature reviewed looked at early amniotomy, whereas I believe there is a need to look at amniotomies performed late in the first stage to augment to second stage, or within the second stage itself. There may be less concern if the procedure is performed in the second stage, as delivery is hoped to be imminent, but it also begs the questions as to why this is being done and why it is considered necessary at this stage. Cluett et al (2004) see the need for amniotomy as marking the transition from midwifery-led care to obstetric-led care. Their work challenges the use of amniotomy to augment a dystocia labour, and also proposes that the use of the pool can be just as effective, if not more so, at improving the progress of labour. From this point, there is a suggestion that power is not primarily influenced by performing ARM – creating the right ambience can cause oxytocic surges that improve power. This leads to a further question regarding power and positioning of the mother – will any malpresentation correct itself and lead to the desired progress?


Sadly, when performing a literature search for en caul birthing, there was very little to be found. Is it that en caul is seen in today’s midwifery as an exceptional phenomenon rather than the norm? On a personal note, while attending an en caul birth with one of my midwifery students, she virtually ran out of the room to get me crossed off the register for allowing it to go ahead. She eventually saw that it was necessary to perform ARM, and after much discussion and thought she now, as a qualified midwife, is much more open to such birthing presentations.





Many women will describe their impression of the onset of birth by using the phrase ‘breaking of the waters’, when in reality this may not signal the start of labour. There is almost a public conditioning in expecting the waters to break and the impression that you cannot possibly be in labour if the membranes remain intact. What damage are we doing with all our interventions? Are we not losing our biological confidence in the birthing process? Over the history of life on earth, birth has brought us to the 21st century. Admittedly, some of our problems can be attributed to another biological drive – the survival of the fittest, but I think many are the result of interference and the feeling that we need to control nature. How sad that we see nature with all its patterns and forms as some weakness, compared with man’s socalled intellectual development to question and control. It seems that in our desire to question, we create more problems that need to be answered. Habits are hard to break and it is my opinion that routine practices such as amniotomy are performed as a means to an end, this end being a speedier delivery. As this article has argued, this is not necessarily the case.


 Further information


For more information about en caul births, please visit: www.midwives.net/hsh/caul.htm




Cluett ER, Pickering RM, Getliffe K, Saunders NJ. (2004) Randomised controlled trial of labouring in water compared with standard of augmentation for the management of dystocia in the first stage of labour. See: www.bmj.bmjjournals.cpm/cgi/ content/full/328/7435/314 (accessed April 2005). Fraser WD, Marcoux S, Moutquin J, Christen A. (1993) Effect of early amniotomy on the risk of dystocia in nulliparous women. The New England Journal of Medicine 328(16): 1145-9. Friedman EA. (1978) Labor, clinical management (second edition). Appleton Century-Crofts: New York. Shaw S, Anderson J. (1999) Membrane rupture vs intact membranes during oxytocin labour induction – evidence centre report. See: www.med.monash.edu.au/healthservices/cce/ evidence/pdf/c/115.pdf (accessed April 2005). Thornton JG, Lilford RJ. (1994) Active management of labour: current knowledge and research issues. British Medical Journal 309(6951): 366-9. Vincent M. (2003) Progress in a pocket – part one. RCM Midwives Journal 6(2): 82-4. Vincent M. (2003) Progress in a pocket – part two. RCM Midwives Journal 6(2): 122

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