Induction of Labor: Balancing Risk

In Australia 25% of labours are induced. The most common reason for induction is a ‘prolonged pregnancy’. That’s an awful lot of babies outstaying their welcome and requiring eviction. I am not going to get stuck into the concept of a ‘due date’ and how accurate or not they are, otherwise this will be a very long post. I also think the EDD (estimated date of delivery) is here to stay – it is deeply embedded in our culture and health care system. You can read about the history of timelines in birth in my previous post. This post will focus on induction for prolonged pregnancy and the complexities of risk.

A quick word about risk

I don’t particularly like the concept of ‘risk’ in birth. There are all knds of problems associated with providing care based on risk rather than on individual women. However, risk along with due dates is here to stay and women often want to know about risks. Risk is a very personal concept and different women will consider different risks to be significant to them. Everything we do in life involves risk. So when considering whether to do X or Y there is no ‘risk free’ option. We choose the option with the risks we personally are most willing to take. In order to make a decision we need adequate information about the risks involved. If a health care provider fails to provide adequate information they could be faced with legal action. Induction for prolonged pregnancy is not right or wrong if the choice is made by an individual woman who has an understanding of all the options and associated risks. As a midwife I am ‘with woman’ regardless of her choices. It is my job to share information and support decisions.

What is a prolonged pregnancy?

Before we go any further lets get some definitions clear:

* Term (as in a ‘normal’ and healthy gestation period): is from 37 weeks to 42 weeks.
* Post dates: the pregnancy has continued beyond the decided due date ie. is over 40 weeks.
* Post term: the pregnancy has continued beyond term ie. 42+ weeks.

The World Health Organization definition of a ‘prolonged pregnancy’ is one that has continued beyond 42 weeks ie. is post term. I am pretty sure that this is was not the definition used when collecting the above induction rate statistics because most hospitals have a policy of induction at 41 weeks which is before a prolonged pregnancy has occurred. Very few women experience a prolonged pregnancy.

In theory after term ie. 42 weeks the placenta starts to shut down. There is no evidence to support this notion and Sara Wickham gives a great critic of this theory if you ever get the chance to attend her workshops. I have seen signs of placental shut down (ie. calcification) in placentas at 37 weeks and I have seen big juicy healthy placentas at 43 weeks. There is also the idea that the baby will grow huge and the skull will calcify making moulding and birth difficult. Again there is no evidence to support this theory and babies are pretty good at finding their way out of their mothers expandable pelvis. Claire Hall has written a great post on ‘big babies’.

The risks associated with waiting

Essentially the main risk associated with waiting beyond 41 weeks gestation is the death of the baby (perinatal death). A Cochrane review found that: “There were fewer baby deaths when a labour induction policy was implemented after 41 completed weeks or later.” However, it goes on to say: “…such deaths were rare with either policy…the absolute risk is extremely small. Women should be appropriately counselled on both the relative and absolute risks.” Hands up all the women who had a discussion with their care provider about the relative and absolute risks of waiting vs induction… hmmm thought so.

I am also going to fail to clarify the absolute and relative risks for you. I am a qualitative researcher by nature and find numbers difficult to grasp. Therefore, I contacted a couple of statistician colleagues who attempted to explain the differences in simple terms. The end result = they got a little frustrated with me and told me to forget relative risk because it is not helpful and to stick with absolute risk. So here goes:

The absolute risk of perinatal death was: 0.03% for the induction group and 0.33% for the waiting group. Either way we are talking about a less than 0.5% risk of perinatal death whether you induce or wait… or a 99.5+% chance of a live baby.

The risks associated with induction

It can be difficult to untangle and isolate the risks involved with induction because usually more than one risk factor is occurring at once (eg. syntocinon, CTG, epidural). I did attempt to create a mind map but it ended up looking like a spider had spun a web while under the influence. So I have stuck to a written version:

Risks associated with the actual procedure of induction

The induction process is a fairly invasive procedure which usually involves some or all of the following. There are a number of minor side effects associated with these medications/procedures (eg. nausea, discomfort etc.) There are also some major risks:

* Prostaglandins (prostin E2 or cervidil) to ripen the cervix: hyperstimulation resulting in fetal distress and c-section.
* Rupturing the membranes: fetal distress and c-section (see previous post)
* IV syntocinon / pitocin: Mother – rupture of uterus; post partum haemorrhage; water intoxication leading to convulsions, coma and/or death. Baby – hypoxic brain damage; neonatal jaundice; neonatal retinal haemorrhage; death.

The most extreme of these risks are rare but fetal distress and c-section are fairly common.

Risks associated with factors that commonly occur during an induction

A woman having her labour induced is more likely to end up with a c-section. This is particularly significant for women having their first baby. A recent research study by Ehrenthal et al. (2010) found an increased c-section rate of 20% for women being induced with their first baby. They concluded that: “Labor induction is significantly associated with a cesarean delivery among nulliparous women at term… reducing the use of elective labor induction may lead to decreased rates of cesarean delivery for a population.” Another study by Selo-Ojeme et al (2010) found induction increased the chance of a c-section x3 for first time mothers. It is now well established that there are significant risks associated with c-section for both mother and baby. Childbirth Connection provide an extensive and evidence based list.

Induced labour is usually more painful than a physiological labour. Syntocinon (aka pitocin) produces strong contractions often without the gentle build up and endorphin release of natural contractions. In addition unlike natural oxytocin, syntocinon does not cross the blood-brain barrier to create the spaced-out, relaxed feelings that help women to cope with pain (see previous post). First time mothers are more than 3x more likely to opt for an epidural (Selo-Ojeme et al. 2010). A Cochrane review found an association between epidural analgesia and instrumental birth. There are significant risks associated with ventouse and forceps birth both for the mother and baby – RANZCOG lists them here.

The study by Selo-Ojeme et al. (2010) also found induction = increased risk of uterine hyperstimulation; ‘suspicious’ fetal heart rate tracings; and haemorrhage following birth. Not surprisingly ‘babies born to mothers who had an induction were significantly more likely to have an Apgar score of <5 at 5mins and an arterial cord pH of <7.0? (basically not in a good way on arrival). Another recent study by Elkamil et al (2011) ‘found that labour induction at term was associated with excess risk of bilateral spastic CP [cerebral palsy]..’ Remember we are inducing labour to prevent harm to the baby…

The experience of labor

Once again the Cochrane review states: “Women’s experiences and opinions about these choices have not been adequately evaluated.” This is becoming a theme across Cochrane reviews. However, one thing is certain – choosing induction will totally alter your birth experience and the options open to you. Women need to know that agreeing to induction means agreeing to continuous monitoring and an IV drip, which will limit movement. Induced contractions are usually more painful than natural contractions and the inability to move and/or use warm water (shower or bath) reduces the ability to cope. The result is that an epidural may be needed. An induced birth is not a physiological birth and requires monitoring (vaginal exams) and time frames. Basically you have bought a ticket on the intervention rollercoaster. For many women this is fine, but I encounter too many women who are unprepared for the level of intervention required during an induction.

Alternatives to waiting or medical induction

Before labour begins the uterus and cervix need to make physiological changes ready to respond to contractions. It is now thought that the baby is the controller of the labour ‘on’ switch. So, the baby signals to the mother that he/she is ready, oxytocin is released and the uterus responds. In comparison to other mammals, humans have the most variable gestation lengths. This suggests that other factors such as environment and emotions (eg. anxiety) also influence the start of labour. This would make sense considering what we know about the function of oxytocin (see previous post). It is also something most midwives are aware of – a stressed out mother is more likely to go post term than a relaxed and chilled out mother. Having said that, post term is probably the normal gestation length for many women regardless of what is going on. Creating anxiety and stress around due dates and impending induction is probably counter productive to labour.

As a midwife I don’t personally recommend methods to encourage labour for women who don’t want induction. Instead I encourage them to trust their body/baby and to ‘look after themselves’ ie. relax and eat well. My general approach to birth is – trust, patience and acceptance. However, I know that many women want to try something to start their labour and there a number of alternative methods in use - BellyBelly covers most of them here.

In Summary

A significant minority of babies will not be born by 41 weeks gestation. Whilst the definition of a prolonged pregnancy is 42 weeks+, induction is usually suggested during the 41st week. Women need to be given adequate information about the risks and benefits involved with either waiting or inducing in order to make the choice that is right for them. There is no risk free option. The risk of perinatal death is extremely small for both options (less than 0.5%). I know women who have lost a baby in the 41st week of pregnancy, and women who have lost a baby as a result of the induction process. Each individual woman must decide which set of risks she is most willing to take.