Episode 2 Induction of Labour

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"Hi, my name is Julia Francis. I'm one of the obstetricians at the Mercy and I'm going to talk you through induction of labour.

We know that induction of labour occurs in about a quarter of all pregnancies, and it is generally recommended when the risk benefit equation of induction versus remaining pregnant favours induction. This equation relies on an accurate assessment of the indication for induction of labour, the gestational age, the maternal and fetal suitability for induction of labour, and some understanding regarding maternal tolerance to risk in order to avoid medical procedures around childbirth.

There are many indications for induction of labour, and a short summary of these includes maternal indications, so prolonged pregnancy; maternal medical conditions such as hypertensive disorders, diabetes or renal disease; pre labour rupture of membranes, antepartum hemorrhage or psychological factors. Some fetal indications would be multiple pregnancy or suspected or likely in utero placental insufficiency.

Risks of induction of labour require an accurate assessment of the gestational age. Especially as we know that inaccurate assessment of gestational age may lead to inadvertent pre or post term induction of labour. Earlier birth gestation may be associated with respiratory distress syndrome or poor feeding. There are specific risks associated with each method of induction, which we'll talk through as we go along. And we know that there is a risk of caesarean section following attempted induction of labour. However, multiple studies have shown that this is not increased overall.

Assessment of suitability for induction of labour includes abdominal palpation to assess the fetal lie and station. We know that a high and mobile head is essentially a contraindication to induction of labour. A vaginal examination should be then performed to assess cervical favourability and calculate a Bishop score. We know that this predicts the likelihood of an uncomplicated vaginal birth, but it also plays into our risk benefit equation around timing. We know that less favourable women are probably less likely to spontaneously labour, and therefore may be associated with increased risks of remaining pregnant, as they will probably remain pregnant longer without medical intervention.

The contraindications to induction of labour are things that are contraindications to vaginal birth, generally, things that are contraindications to oxytocics, and things that are contraindications to artificial rupture of membranes. Contraindications to vaginal birth are things like malpresentations such as a breech, a placenta previa, or a vasa previa, or a previous classical caesarean section.

Contraindications to oxytocics are generally relative rather than absolute, and these are either grand multiparity or previous caesarean section, things that increase the risk of a uterine rupture. As mentioned previously, a high and mobile presenting part is a contraindication to an ARM (artificial rupture of membranes) given the associated risk of a cord prolapse. Induction, essentially aims to mimic spontaneous labour. So, I'll just go back to some of the factors that we know initiate labour. And essentially this occurs when the factors favoring uterine activity overcome the factors favoring quiescence. So, this is an increase in corticotrophin releasing factor in increasing estrogen efficacy and a reduction in progesterone efficacy.

Induction of labour involves cervical ripening, rupture of membranes and then uterine contractions that aim to cause cervical effacement and dilatation. The process of induction of labour includes an initial assessment. So, a history and an understanding of that evaluation regarding the risk, benefit, and timing of induction. Abdominal palpation to work out the lie and station and assessment of fetal well-being with a CTG and perhaps an ultrasound, and then a vaginal examination to calculate the bishop's score based on dilatation, position of the cervix, cervical effacement station and cervical consistency. And we know that a lower bishop's score means an increasing need for cervical ripening. Cervical ripening can be undertaken with pharmacological or mechanical methods. Pharmacological methods of prostaglandins such as prostin or cervidil. These promote uterine activity, however, are associated with the risk of hyper stimulation, which can lead to fetal distress or uterine rupture.

The mechanical method of cervical ripening used is a trans cervical balloon catheter. In general, in obstetrics, we use dinoprostone, which is a prostaglandin E2 or prostin, used as a one milligram trial dose, and then repeat doses up to five milligrams given six hours apart. Given the risk of hyper stimulation, CTG needs to be performed prior to and after the insertion of prostaglandin to check on fetal well-being. There is also a slow-release version of dinoprostone called cervidil, which is generally in for 12 or 24 hours prior to induction. Around the world, misoprostol is also used as a cervical ripening agent. It's highly effective at causing uterine contractions but is increasingly associated with a risk of hyper stimulation or FDIUs, so not used in our context.

The main adverse effects of prostaglandins we've mentioned previously, but essentially excess uterine activity, which is associated with a reduction in utero placental blood flow with each contraction, which can cause fetal hypoxia or acidosis. Excess thinning of the lower segment can occur as the upper segment contracts vigorously around the fetus, and this can be associated with a risk of uterine rupture, and prostaglandins are associated with an increased risk of amniotic fluid embolus.

Just as a quick recap, management of hyper stimulation includes placement of a continuous CTG, discontinuation of any oxytocin or removal of prostaglandin, intrauterine resuscitation, including left lateral position, administration of fluids. If maternal hypertension is present and then tocolytics the form of salbutamol, terbutaline or GTN, and some assessment as to whether the situation has resolved or urgent delivery with caesarean section is required.

Contraindications to prostaglandins we've mentioned previously. So those are conditions which predispose to scar rupture, grand multiparity or previous scar rupture or concern regarding fetal reserves. The trans-cervical balloon catheter is either a Foley balloon or a double balloon catheter, such as a Cooks balloon, which is inserted trans-vaginally. It's generally inserted the day prior to an induction of labour. The main risk is a theoretical concern of infection, so it's put in under aseptic technique. And patients who are GBS positive would receive intravenous antibiotics. There is also a small risk of displacing the fetal head or causing an unstable lie, so a vaginal exam should be performed prior to ARM to confirm appropriateness.

We know that artificial rupture of membranes works because it increases endogenous prostaglandins, which augment uterine muscular activity and increase receptivity to oxytocin. The fetus then exerts more pressure on the cervix, which, via the Fergus reflex, promotes more endogenous oxytocin release. The main adverse effect with an artificial rupture of membranes is the risk of a cord prolapse. Following ARM, an oxytocin infusion is then commenced. This is generally ten units of cytosine in a litre of Hartmann's. It's commenced at 12 units an hour and increased in 12 ml increments over 30 minutes until the patient is in good labour, experiencing 4 in 10 moderate to strong contractions.

The duration and frequency of contractions should be assessed every 15 minutes, and given the potential impact on placental blood flow, all inductions with oxytocin require continuous electronic fetal monitoring. The adverse effects of oxytocin are excess uterine activity, risk of hypotension, risk of water intoxication, and risk of postpartum hemorrhage. As we know that oxytocin down regulates its own receptor, so it does reduce the sensitivity to endogenous oxytocin if the high-level infusion is ceased.

Management of labour following induction is continuous electronic fetal monitoring, analgesia as required, regular maternal observations, including abdominal palpation, timing of contractions and assessment of the CTG. Vaginal assessment four hours after the establishment of labour and four hourly thereafter, and expectation and prompt management of the risk of a postpartum hemorrhage after delivery.

Quickly touching on some specific indications and timing of induction of labour. In general, post states, induction of labour is recommended at 41 to 41 plus three weeks. Given the risks of post term pregnancy pre labour rupture of membranes, we know that the term from trial showed early versus late induction was associated with reduced risk of neonatal and maternal infection. So, induction should be offered within 24 hours in the GBS negative group. If there is a reassuring maternal and fetal status and should be offered immediately in GBS positive patients.

In the setting of diabetes, we recommend induction of labour around 38 weeks in women with pre-pregnancy diabetes. In the setting of gestational diabetes this depends on the assessment of presence of fetal macrosomia and use of insulin, but generally is recommended by 40 weeks, providing there's no fetal macrosomia.

In twins we recommend delivery in the 36th week for monochorionic twins and in the 37th week for dichorionic twins. This is because we know there's an increased risk in perinatal mortality earlier in multiples than in singletons.

In the setting of pre-pregnancy or gestational hypertension, we would recommend delivery from 37 weeks. And in the setting of preeclampsia, once the patient reaches 37 weeks, or earlier if there's a maternal or fetal trigger.

In the setting of suspected utero placental insufficiency or fetal growth restriction in the very preterm period delivery is generally made based on the findings of Doppler studies, and we generally recommend delivery by 37 weeks if the baby is estimated under the third centile or under the 10th centile with oligohydramnios or a presence of abnormal Dopplers. We'd recommend delivery between 38 and 39 weeks if the baby's under the 10th centile with normal Dopplers and DVP.

Other conditions that would prompt concern regarding utero placental insufficiency or fetal growth restriction would be persistent reduced fetal movements at term which we would recommend an induction of labour for, or clinical concern regarding the symphysis fundal height less than dates.  Generally three centimetres less than expected on one occasion, or two centimetres less than expected on two occasions would be triggers for recommendation about induction of labour."