Induction of labour

1. What is the aim of induction of labour (IOL)?
Induction of labour aims to trigger the onset of labour to achieve a safe vaginal delivery. IOL is advised when the risks of leaving the fetus in-utero are higher compared with the risks of the procedure of IOL.


2. Special circumstances where IOL might be considered

  • Prolonged pregnancy
  1. (i) Prolonged pregnancy is associated with the risk of decline of the placental function (termed ‘uteroplacental insufficiency’). Epidemiological data have shown a slow increase in perinatal mortality after 40 weeks of gestation. One UK study involving 197,061 women also showed a racial difference in the perinatal mortality after 40 weeks, with South Asians being highest, followed by the black women compared with the white population. However, the overall risks are low, in the order of 2-3/1,000;
  2. (ii) Prolonged pregnancy is also associated with the presence of fetal stool in the amniotic fluid (meconium stained liquor) which predisposes to neonatal meconium aspiration at birth;
  3. (iii) Studies on health economic analysis have found that IOL at ~41 weeks of gestation is more cost-effective compared with IOL at 42 weeks or beyond. In Hong Kong, the common practice is to have an IOL scheduled at ~41 weeks
  • Pre-labour rupture of membranes
  1. (i) Rupture of membranes can precede the onset of labour. Around 85% will have spontaneous labour within the next 24 hours;
  2. (ii) Infection is a concern as infection of the amniotic membrane can be an underlying cause. Also, the rupture of membranes will predispose ascending infection from bacteria in the vagina;
  3. (iii) IOL following rupture of membranes is considered an appropriate practice. The alternative is to wait for spontaneous labour and only to offer IOL if there is no labour after 24 hours
  1. (i) Early delivery may be necessary if the intrauterine environment has hampered the fetal growth;
  2. (ii) IOL before the fetal condition has become critical allows the possibility of vaginal birth. Yet, with limited body reserve, the fetus may not be able to withstand the stress of labour. The alternative option would be a caesarean section. Hence, the risks and benefits of IOL versus caesarean delivery need to be carefully weighed balance
  • Maternal medical conditions

    Common examples of maternal reasons for IOL include diabetes, pre-eclampsia and intrahepatic cholestasis of pregnancy

  • Intrauterine fetal demise
  1. (i) Following the unfortunate event of intrauterine fetal demise, an attempt of vaginal delivery is advised and unless there is maternal risk, caesarean section should be avoided;
  2. (ii) There is no evidence that IOL needs to be arranged immediately unless there is bleeding, rupture of membranes, evidence of infection or maternal complications such as hypertension. However, most women would prefer an early IOL;
  3. (iii) Oral or vaginal prostaglandins are used. Amniotomy should be avoided
  • History of precipitate labour
  1. (i) Precipitate labour is defined as expulsion of the fetus within 3 hours of commencement of contractions. The main risk is that the mother may not be able to arrive at the obstetric unit when she labours again in the subsequent pregnancies. Babies born before arrival are at risks of infection and low temperature. For the mother, it would be an extremely inconvenient and embarrassing situation and most would like to avoid;
  2. (ii) There is no randomised controlled study to address IOL in this condition;
  3. (iii) While some authorities do not view that IOL is indicated, it is in my opinion that IOL can be considered. It should be the women’s decision after knowing the pros and cons
  • Suspected fetal macrosomia
  1. (i) Macrosoma is defined as a birthweight > 4 kg. The estimation of the fetal weight by antenatal ultrasound is not without limitation. It carries an error of +/- 15%;
  2. (ii) Systematic reviews of randomised controlled studies do not demonstrate any evidence in reduction of caesarean section rates or improved maternal or neonatal outcomes with IOL for suspected macrosomia
  • Maternal request
  1. (i) IOL on maternal request without medical indication has been criticized by some authorities as unnecessary intervention which carries procedure-related risks;
  2. (ii) Yet it is not uncommon for some women to request for an earlier vaginal delivery to suit their social or psychological reasons. The question is whether the risks of IOL can be outweighed by the benefits;
  3. (iii) It was traditionally worried that early IOL is associated with a higher induction failure and hence higher caesarean section rates. However, there is new evidence from a large randomised controlled trial published in 2018 that earlier IOL for low-risk nulliparous women at 39+ weeks of gestation may result in lower risk of caesarean delivery;
  4. (iv) It is in my opinion that rather than to say that IOL is ‘not necessary or bad’, the women who made the request should be allowed to cite their reasons and express their concern. A careful assessment should be carried out on factors like engagement of the fetal head and cervical status, which may help to predict how easy (or difficult) the IOL will be. The women should be given all the information including the chance of a failed IOL before a decision is made

3. How is IOL carried out?

  • If the cervix is favourable, IOL is commonly carried out by amniotomy (rupturing the amniotic membrane through the vagina by midwife or obstetrician) and then infusion of oxytocin (medication to stimulate labour) through the vein of the mother. The dosage of the oxytocin has to be individualised and titrated against the uterine contractions;
  • If the cervix is not favourable, vaginal prostaglandins tablet(s) are used to improve it (called ‘to ripen the cervix’) before amniotomy and oxytocin infusion

4. Pain relief during IOL
Data from randomised controlled studies have shown that

  • Epidural analgesia offers better pain relief compared with no epidural analgesia;
  • Early use of epidural analgesia in the process of IOL does not prolong the labour duration or increase the rates of instrumental vaginal delivery or caesarean section

5. Risks of IOL

  • Failure – will end up as emergency caesarean section;
  • Fetal risks – abnormal fetal heart tracing. Continuous fetal heart monitoring is essential;
  • Maternal risks –
  1. (i) Thromboembolism due to prolonged bed rest
  2. (ii)Very rarely, amniotic fluid embolism which is very serious and life-threatening

6. Prediction of success of IOL

Favourable factors include:

  • Young maternal age;
  • Previous vaginal delivery;
  • Soft and lax cervix;
  • Roomy pelvis
  • Lack of pregnancy complications
  • Smaller baby
  • Deep head engagement into the mother’s pelvis
  • Fetus facing down

It is important to realise that success of IOL cannot always be predicted accurately

7. What is the difference between IOL and augmentation of labour?
Sometimes following the spontaneous onset of labour, the progress can be slow. There are 3 common reasons in the case of first-time mothers (nulliparous women):

  • Inefficient uterine contractions
  • Fetal head position not optimal (such as face up position)
  • Cephalo-pelvic disproportion (baby’s head size too big for the woman’s pelvis)

To optimize the uterine contractions, an amniotomy and oxytocin infusion are commonly practised. This is called ‘augmentation of labour’. The procedures are similar to the case of IOL.

This article is contributed by Dr. T.N. Danny Leung
Updated on 24.04.2023