Post-Dates Induction of Labour: balancing risks

Updated: August 2019

In Australia 33% of labours are induced (40.5% of first time mothers). The most common reason for induction is to prevent 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 ‘due dates’ or rather ‘guess dates’ here – I discuss estimating birth dates in my book. This post will focus on induction of labour to prevent a ‘prolonged’ pregnancy and the complexities of risk in this situation.

A quick word about risk

I don’t particularly like the concept of ‘risk’ in birth. There are all kinds 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 usually 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. All women can do is choose the option with the risks they are most willing to take. However, in order to make a decision women need adequate information about the risks involved in each option. 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 a 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 – not to judge.

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 (guess) date ie. is over 40 weeks.
  • Post-term: the pregnancy has continued beyond term ie. 42+ weeks.

The World Health Organization’s definition of a ‘prolonged pregnancy’ is one that has continued beyond 42 weeks ie. is post-term. However, induction is usually offered when a pregnancy becomes post-dates with the aim of preventing it becoming ‘prolonged’. Therefore, very few women experience a prolonged pregnancy – in Australia only 0.6% of pregnancies continue beyond 42 weeks.

The idea of a prolonged pregnancy assumes that all women naturally gestate their babies for the same length of time. However, it seems that genetic differences may influence what is a ‘normal’ gestation time for a particular woman. For example, Morken, Melve and Skjaerven (2011) found “a familial factor related to recurrence of prolonged pregnancy across generations and both mother and father seem to contribute.” Therefore, if the women in your family gestate for 42 weeks so might you. The length of gestation may also be influenced by factors such as diet (McAlpine et al. 2016).

The initiation of labour is likely caused by the baby who secretes surfactant protein and platelet-activating factor into the amniotic fluid as their lungs mature (Mendelson 2009; Science Daily). This results in an inflammatory response in the mother’s uterus that initiates labour.

The risks associated with waiting for spontaneous labour

Ageing placenta?

Some people believe that the placenta has a best before date and starts to deteriorate after 40 weeks resulting in reduced nutrition and oxygen for the baby. There is evidence that the structure and biochemistry of the placenta changes as pregnancy develops. Some scientists interpret these changes as the placenta growing and adapting to meet the changing needs of the baby: “There is, in fact, no logical reason for believing that the placenta, which is a fetal organ, should age while the other fetal organs do not…” Others argue that these changes are due to the ageing and deterioration of the placenta. However, tests of placental function show no changes in post-dates pregnancies (Madruzzato et al. 2010). In practice, 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. Sophie Messenger write more about ‘the myth of the ageing placenta’ here.

Big baby

People also have concerns that the baby will grow huge and therefore be difficult to birth. There is evidence that babies continue to grow bigger the longer they gestate, and this contradicts the above theory about the ageing placenta. If the placenta stops functioning, how does the baby continue to grow so well? Big babies are pretty good at finding their way out of their mothers expandable pelvis. The research about complications relating to big babies suggests that it is the interventions carried out when a baby is assumed to be big – rather than the actual size of the baby – that mostly contributes to complications (Sadeh-Mestechkin et al. 2008; Blackwell et al. 2009; Peleg et al. 2015).

Meconium liquor

There is an increased chance that the baby will pass meconium as his/her bowels mature. I have written about this scenario in another post.

Perinatal death

The general rate of perinatal death (stillbirth + newborn death) increases as pregnancies advance beyond term. The rate remains small but is statistically significant. For example a systematic review and meta-analysis (Muglu et al. 2019) reported that: “The overall gestation-week-specific prospective risk of stillbirth steadily increased with gestational age, from 0.11 per 1,000 pregnancies at 37 weeks to 3.18 per 1,000 at 42 weeks gestation… The risks of newborn death remained constant between 38 and 41 weeks, and only increased beyond 41 weeks” .

Post-dates induction of labour reduces the general rate of perinatal death. A Cochrane Review summarises the research examining induction vs waiting: “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…

Essentially, according to the available research, if you are induced at 41 weeks your baby is less likely to die during, or soon after birth. However, the chance of your baby dying is small either way – less than 1%… or 30 out of every 10,000 for those waiting vs 3:10,000 for those induced. This research article reports the relative and absolute risk of stillbirth at various gestations with waiting vs induction. The authors state that 1476 women would need to have an induction to prevent 1 stillbirth at 41 weeks gestation.

Reviews are only as good as the research they review and there are some concerns about the quality of the available research. The World Health Organization recommends induction after 41 weeks based on the Cochrane Review above but acknowledges the evidence is “low-quality evidence. Weak recommendation”.  Another review of the literature in the Journal of Perinatal Medicine (Mandruzzato et al. 2010) concluded: “It is not possible to give a specific gestational age at which an otherwise uncomplicated pregnancy should be induced.”

One of the main problems with quantitative research is that it rarely answers the question ‘why’, and rather focuses on ‘what’ (happens). For example, congenital abnormalities of the baby and placenta are associated with post-term pregnancy and this may account for the increased risk in some cases, rather than the length of gestation (Mandruzzato et al. 2010). Quantitative research also takes a general perspective rather than addressing the risk for an individual woman in a particular situation. For example, is the prolonged pregnancy as sign of pathology, or does this woman come from a family of women who have a longer gestational timeframe? For a woman who has previously gestated to post-term without complications, there is no increased chance of an adverse outcome (Kortekaas et al. 2015).

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). In addition, there are differences in outcomes and risks between women who have previously laboured, and women having their first baby. It is important for women to consider their own individual factors and how they alter their individual risk profile. Care providers should also share individualised information when discussing induction options.

General risks associated with the induction procedure and medications

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

The most extreme of these risks are rare, but fetal distress and c-section are fairly common. The potential effects of uterine hyperstimulation on the baby are well known (Simpson & James 2008)- which is why continuous fetal monitoring is recommended during induction. This may also explain the association between induction and cerebral palsy (Elkamil et al. 2010)

Induced contractions are usually more painful than a physiological contractions. Syntocinon (pitocin) produces strong contractions without the gentle build up and endorphin release of natural contractions. The National Institute of Clinical Excellence (UK) state that health care professionals should discuss this with women when offering induction “recognising that women are likely to find induced labour more painful than spontaneous labour”.

Most research comparing induction with spontaneous labour combines populations of ‘experienced’ labourers with first timers. These studies report conflicting findings. For example, some studies report a lower chance of c-section with induction for this mixed group (Gülmezoglu et al. 2012; Mishanina et al. 2014Wood et al. 2014). In contrast, more recent studies have found increased rates of c-section with induction (Zhao, Flatley, Kumar 2017; Ekéus & Lindgren 2016). A 2019 review compared the timing of induction for low risk pregnancies – 41 weeks vs 42 weeks (Rydahl, Eriksen & Juhl 2019). The review used stricter inclusion criteria than previous reviews to “enhance the methodological quality and increase the relevance for contemporary maternity care”; and reported that: “Induction at 41+0-6 gestational weeks compared to 42+0-6 gestational weeks was found to be associated with an increased risk of overall cesarean section.”

Risks for women who have had a previous labour

Women who have laboured before respond more effectively to syntocinon (pitocin) because they have more oxytocin receptors in their uterine muscle. Therefore, this group of women are more likely to experience a successful induction and avoid c-section. They are likely the reason for lower or similar rates of c-section the mixed group research discussed above. However, they are at increased risk of hyperstimulation with prostaglandin medication and/or syntocinon. So doses are usually smaller and very carefully monitored to avoid fetal distress. Women who have given birth vaginally before, are also at increased risk of perineal tearing if they have syntocinon induced contractions.

Risks for women having their first labour induced

Inducing a first labour requires higher rates of syntocinon, and the length of labour is usually longer. It is not surprising that first time mothers are more than 3 x more likely to opt for an epidural during an induction (Selo-Ojeme et al. 2011); and epidural analgesia increases the chance of ending up with an instrumental birth – ventouse or forceps (Anim-Somuah et al. 2018)

The majority of research comparing induction (IOL) with spontaneous (SP) labour in populations of first time labourers report increased c-section rates:

Another US study (Ehrenthal et al. 2010) reported that after “adjusting for maternal demographic characteristics, medical risk, and pregnancy complications. The contribution of labor induction to cesarean delivery in this cohort was estimated to be approximately 20%.” This brings up interesting risk comparisons relating to c-section vs the risk of post-dates perinatal death (see above). For example, induction is recommended because there is a less than 0.3% chance of perinatal death in post-dates pregnancies (see above). However, the chance of a significant complication during c-section (eg. hysterectomy) is higher than the chance of perinatal death in a post-dates pregnancy; and after a c-section the chance of stillbirth during a subsequent pregnancy increases to 0.4% – again, a higher rate than a postdates pregnancy.

A recent study causing a stir is the ARRIVE RCT trial (US) which reported lower c-section rates in the induction group (18.6% vs 22.2%). This one study is now being used to justify recommending early induction at 39 weeks – primarily because the findings align with cultural norms and preferences (see this post re. implementation of research findings into practice). Whilst I don’t want to give this study unwarranted attention… it keeps popping up in conversations, workshops, and presentations. Like the perineal bundle – it is an unavoidable topic in the birth world. So here goes (briefly)… recommendations based on the trial are problematic in a number of ways. The findings and recommendations have been constructively critiqued by academics, midwives and obstetricians (Dekker 2018; Carmichael & Snowdon 2019; Davis-Tuck et al. 2018; Scialli 2019). In summary, the main points are:

  • Only 27% of eligible women agreed to participate – Findings can only be applied to women who are willing to have a medically managed birth.
  • 94% of the woman were cared for by private obstetricians in US medical settings – Findings cannot be applied to other types of care providers and settings which have much lower rates of c-section and higher rates of spontaneous vaginal birth.
  • Care providers were not blinded – Knowing about the trial my have altered their practice.
  • IOL reduced c-section rates by 4% – This cannot be used to recommend IOL to prevent c-section. Other factors have a much more significant effect on c-section rates eg. continuity of midwifery care; place of birth; intermittent auscultation in labour; etc.
  • The primary outcome measure for this study was perinatal outcome (ie. the baby) – IOL made no difference to the immediate outcomes for the baby, and the study did not address the long-term harm of early birth for the baby (eg. brain development).

In relation to the primary outcome measure – perinatal outcomes. Another study (Selo-Ojeme et al 2011) found that outcomes for the baby were worse when a first labour was induced: “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“. 

The experience of induction

Research into induction tends to focus on physical outcomes rather than women’s emotional/psychological experiences of the process.

Choosing induction will totally alter the 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 and worth the risk, but I encounter too many women who are unprepared for the level of intervention required during an induction. This does not mean you have to hand over control of your decisions or your body; and in my book I include a chapter on creating a birth plan for induction of labour.

There have been some studies examining women’s experience of induction. A UK study by Henderson and Redshaw (2013) found that “women who were induced were generally less satisfied with aspects of their care and significantly less likely to have a normal delivery. In the qualitative analysis the main themes that emerged concerned delay, staff short- ages, neglect, pain and anxiety in relation to getting the induction started and once it was underway; and in relation to failed induction, the main themes were plans not being followed, wasted effort and pain, and feeling let down and disappointed.”.  A German study (Schwarz et al. 2016) concluded that: “women’s expectations and needs regarding IOL are widely unmet in current clinical practiceand that “there is a need for evidence-based information and decisional support for pregnant women who need to decide how to proceed once term is reached.”

A recent systematic review (Coates et al. 2019) of qualitative research into women’s experiences of induction of labour concluded that induction “is a challenging experience for women, which can be understood in terms of the gap between women’s needs and the reality of their experience concerning information and decision-making, support, and environment. “

Alternatives to medical induction

Waiting for spontaneous labour

Around 90% of women who wait for spontaneous labour will give birth before 42 week, and only 1% will go beyond 43 weeks (Gülmezoglu et al. 2012). Most guidelines recommend additional monitoring of the baby – however no form of monitoring reduces the chance of complications (Gülmezoglu et al. 2012).

‘Natural’ induction?

There are a number of ‘alternative’ or ‘natural’ induction methods available (I have a chapter discussing the evidence for various methods in my book). However, trying to get the body/baby to do something it is not ready to do is still an intervention whether it is with medicine, herbs, therapies, techniques… or anything else. Interventions of any kind can have unwanted effects and consequences. Medical inductions take place with close monitoring of mother and baby and access to medical support if a complication arises. Alternative inductions do not have this level of monitoring or back up.

However, ‘interventions’ (massage, acupuncture, etc.) that are aimed at relaxing the mother and fostering trust, patience and acceptance may assist the body/baby to initiate labour if the physiological changes have already taken place.


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. 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. For first time mothers the induction process poses particular risks for themselves and their babies. Each individual woman must decide which set of risks she is most willing to take – and be supported in her choice.

You can read more about induction in my book Why Induction Matters

Further resources