Induction of labour – Medical and Surgical Methods

• When is labour induced?
• Your cervix
• How to induce labour
  • Transcervical foley catheter
  • How to bring on labour with prostaglandins
  • Inducing labour by artificial rupture of membranes
  • How to induce labour with oxytocin
• Risks associated with induction of labour

 

The induction of labour (IOL) is a relatively common procedure where labour is initiated prior to pregnant women going into labour and vaginal birth naturally themselves. There are medical and surgical ways of inducing labour, some pregnant women also try natural ways of inducing labour.

When is labour induced?

Inducing labour is usually reserved for situations where the benefits of delivering the baby outweigh the risks of continuing the pregnancy. Just over one quarter of all labours in Australia are induced.

Some situations where IOL is performed includes:

• Prolonged pregnancy (that goes beyond 41 weeks)
• Where a woman’s waters have broken prior to the onset of labour in a term pregnancy (a pregnancy 37 or more weeks gestation)
• At the request of the pregnant mother (only where exceptional circumstances exist)
• Gestational diabetes (diabetes in pregnancy) requiring insulin for treatment
• Cholestasis of pregnancy (a condition of pregnancy where the pregnant mother experiences itch without a rash, which is associated with specific abnormal blood results)
• Hypertension (high blood pressure) in pregnancy based on individual circumstances

There are some situations where IOL shouldn’t be performed including:

• Abnormalities of the placenta such as low lying placenta (placenta praevia)
• Abnormalities of how the baby is lying (malposition or malpresentation)
• Where the pelvis is too small for the passage of the head of the baby (cephalopelvic disproportion)
• Where the pregnant mother refuses
• Where the umbilical cord is the presenting part or has prolapsed into the vagina (cord prolapse)
• Active genital herpes
• HIV infection

Your cervix

The process of IOL can vary depending on the condition of your cervix. There is a scoring system, known as the Bishop score, that is used as a scoring system to assess the cervix. A modified Bishop’s score is also available. The difference between the two is that the original Bishop’s score includes cervical effacement (0-30%, 31-50%, 51-80% and >80%) which has been  replaced in the modified Bishops’s score with cervical length (>3cm, 2cm, 1cm, <1cm). Given that the cervical length is representative of the amount of cervical effacement (thinning of the cervix as it stretches) both measure the same cervical feature just in different scales. Both scoring systems give the same end result and are therefore used in the same way. They are important as you are more likely to have a successful induction if your score is 7 or more. The cervix is said to be unfavourable for induction of labour if the Bishop’s score is 6 or less. These women will need to undergo cervical ripening which can be by means of a prostaglandin based gel/controlled release or a transcervical foley catheter. The score is based on a number of factors outlined below.

Dilatation refers to how open or dilated your cervix is. If this is your first baby, your cervix may be closed (a score of zero), or if this is not your first pregnancy your cervix may already be dilated 1-2cm. Your cervix is fully dilated when it reaches 10cm and it is this stage that you are ready to ‘push’ and deliver your baby.

The length of your cervix refers to how long it is. Initially the cervix is long and as labour progresses it shortens/flattens out until the point that it is very thin. If this is your first baby the cervix usually shortens/flattens before it dilates. If this is not your first pregnancy it is likely that your cervix with shorten/flatten at the same time as it dilates.

Station refers to how far into the pelvis your baby’s head is sitting. The minus sign indicates that your baby’s head is sitting higher in the pelvis, while a positive sign indicates that your baby’s head is lower in the pelvis.

Consistency refers to how your cervix feels, if it is soft and stretchy, medium or firm.

Position refers to where your cervix is sitting. Often prior to or in early labour the cervix is located towards the back (posterior) and as labour progresses it moves forward into a mid or anterior position.

Figure 1. Modified Bishop’s score

Cervical features	Score
	0	1	2	3
Dilation (cm)	< 1	1-2	3-4	> 4
Length of Cervix (cm)	> 3	2	1	< 1
Station (relative to ischial spines)	-3	-2	-1 / 0	+1 / +2
Consistency	Firm	Medium	Soft	–
Position	Posterior	Mid	Anterior	–

 

From the table you can see that you will have a higher score if the cervix has already started to dilate, has shortened, is soft and has moved from a posterior to anterior position.For those women in which the cervix is already ‘ripened’ (a score of 7 or above) or have undergone cervical ripening, the next step of the process of inducing labour is artificial rupture of membranes and commencement of oxytocin infusion.

How to induce labour

If the cervix is favourable, ways to bring on include artificial rupture of membranes and/or oxytocin infusion. For an unfavourable cervix, it must first be ripened using either a transcervical foleys catheter or vaginally administered prostaglandins. Each of these is discussed in detail below.

Transcervical foley catheter

The transcervical foley catheter is one of the means to ‘ripen the cervix’ so it is more favourable for induction. It is a long thin tube that has a balloon at its tip that can be inflated/deflated. During this process the tip of the foley catheter is passed through the canal of the cervix and the balloon then inflated. It is important that the inflated balloon is positioned correctly in order to exert the mechanical pressure needed to dilate (open) the cervix. The opposite end is then taped to your thigh. The main advantage of the foley catheter is that it can be used in situations where it is advisable to avoid pharmacological agents (prostaglandins).

Prior to having the foley catheter inserted, you may be asked to empty your bladder. The position of your baby will be confirmed by palpating (feeling) the abdomen. A cardiotograph (CTG – recording of the baby’s heart rate and contractions of the uterus) will be performed to check the foetal heart rate pattern and the presence/absence of any contractions. If the bishop’s score is unknown an internal cervical assessment/vaginal examination must be made. Some women can find this uncomfortable as it involves the Doctor or Midwife inserting two fingers into the vagina in order to feel the cervix and make an assessment about the cervix’s dilatation, length, position and consistency (Bishop’s score).

The foley catheter can then be inserted if the Bishop’s score is 6 or less. The foetal heart rate and maternal observations (any vaginal fluid loss or bleeding, temperature, pulse, blood pressure and oxygen saturations) will be checked immediately after and 4-hourly thereafter. A vaginal examination will be performed between 12 and 18 hours post insertion to assess the position of the catheter and any change in the cervix.

If there is evidence that the uterus is becoming highly stimulated, the baby is stressed, or if you request it, the catheter will be removed.

How to bring on labour with prostaglandins

Prostaglandin E2 (dinoprostone) provides a pharmacological method of cervical ripening and induction of labour. It is available in the form of a gel (Prostin E2) or as a controlled release (the dose is released over a period of time) pessary (Cervidil) that is inserted into the vagina.

Some reasons why you shouldn’t have prostaglandins include:

• Previous surgery involving the uterus, such as previous caesarean section
• If you have had five or more babies in the past
• Abnormal CTG or suspected foetal compromise
• Known hypersensitivity to the medication
• Any other conditions for which a vaginal delivery is NOT recommended

Caution is used if a woman has certain medical conditions so make sure your doctor is aware of your past medical history.

Prior to inserting the medication into your vagina, you may be asked to empty your bladder. The position of your baby will be confirmed by palpating (feeling) the abdomen. A cardiotograph (CTG – recording of the baby’s heart rate and contractions of the uterus) will be performed to check the foetal heart rate pattern and the presence/absence of any contractions. If the bishop’s score is unknown an internal cervical assessment/vaginal examination must be made. Some women can find this uncomfortable as it involves the Doctor or Midwife inserting two fingers into the vagina in order to feel the cervix and make an assessment about the cervix’s dilatation, length, position and consistency (Bishop’s score).

The prostaglandin can then be inserted if the bishop’s score is 6 or less. Following insertion you should lie on your left side for 30 minutes to allow the medication to be absorbed. A CTG will be recording your baby’s heart rate and any uterine contractions during this period. The foetal heart rate and maternal observations (any vaginal fluid loss/bleeding, temperature, pulse, blood pressure and oxygen saturations) will be checked 4-hourly thereafter. If you develop contractions you will need to have continuous CTG monitoring. A repeat internal exam will be performed six hours post dose to assess any cervical change. If the change is minimal then a second dose can be given.

Complications can include:

• Maternal gastrointestinal symptoms such as nausea
• Uterine overactivity (the uterus contracting too frequently)
• Postpartum haemorrhage (bleeding following the birth of your baby)
• Fever
• Amniotic fluid embolism
• Vaginal irritation and/or
• Back pain

Inducing labour by artificial rupture of membranes

Artificial rupture of membranes (ARM) refers to surgical rupture of the membranes that surround your baby (the amnion and chorion). This can be performed to induce labour if the bishop’s score is 7 or more. Some women, especially those who have had babies previously, may go on to develop contractions spontaneously. Alternatively this method is commonly used in combination with oxytocin (discussed below).

Before your membranes are ruptured, you will most likely be asked to empty your bladder. Following this, the position of the baby will be determined by palpating (feeling) the abdomen. Your baby’s heart rate will also be monitored. The membranes are ruptured while an internal exam is being performed. Once the membranes have ruptured you will experience fluid leaking out of the vagina, this is the fluid that surrounded your baby.

The risks include infection and cord prolapse (where the umbilical cord comes out in front of the baby’s head).Situations where ARM shouldn’t be performed includes:

• Low lying placenta (Placenta praevia)
• HIV infection
• Active herpes lesions
• Abnormalities of how the baby is lying
• Any other conditions for which a vaginal delivery is not recommended

How to induce labour with oxytocin

Oxytocin is the hormone responsible for stimulating the uterus to contract. Synthetic forms of oxytocin (Oxytocin; Syntocinon) are available and these can be administered intravenously (into the vein) to induce labour. This is typically as an infusion where a certain dose of the medication is delivered over a period of time.

Before starting oxytocin it is important that it has been 6 hours or more since your last dose of prostaglandins if you had any, that your membranes have ruptured either naturally or artificially (ARM) and that there are no abnormalities with the foetal heart pattern on CTG. While you are receiving the oxytocin infusion you will need continuous CTG monitoring. This is to monitor your baby’s heart rate as well as determine how many, if any, contractions you are having. The amount of oxytocin given to you is adjusted depending on your response. The aim is to use the lowest dose of oxytocin possible to maintain 3-4 contractions in 10 minutes with each contraction lasting approximately 60 seconds.

Situations where you shouldn’t have an oxytocin infusion include:

• Any condition in which labour is not recommended
• 2 or more previous caesarean sections

Complications that can be associated with oxytocin infusion include:

• Overstimulation of your uterus (Uterine hyperstimulation) – see below
• Water retention
• Low blood pressure (Hypotension)
• Rarely abnormal heart rhythms (arrhythmias) and/or anaphylaxis reactions can occur

Oxytocin can be associated with uterine hyperstimulation. This occurs when:

• Frequency of contractions is five or more within a ten minute period
• Contractions last greater than 90 seconds
• Contractions of a normal duration occur within 1 minute of each other
• The uterus does not completely relax between contractions

If the baby seems unaffected by this it can simply be managed by turning off the oxytocin until the activity returns to normal. If the baby appears stressed (determined by its heart rate pattern) the oxytocin should be stopped promptly and consideration given to the use of medications to stop further contractions. Preparation for immediate vaginal delivery and/or possible caesarean section should be made in the event that the foetal heart rate does not return to normal. Where contractions return to normal and the baby is not stressed, the oxytocin should be restarted at half the rate of the last dose infused and adjusted accordingly.

Risks associated with induction of labour

There are several risks associated with induction of labour which include:

1. Failed IOL – the criteria for failed IOL is generally not well agreed, however, it would include those women that fail to establish labour as well as those that establish labour but then fail to progress despite induction. In such cases, individual circumstances should be reviewed and an assessment of foetal wellbeing made. Options should be discussed with the woman, which may include caesarean section.
2. Uterine hyperstimulation, as discussed above, can occur with either prostaglandin or oxytocin. If this occurs any remaining prostaglandin should be removed. If an oxytocin infusion is running it should be reduced or turned off as per above management plan (discussed under oxytocin)
3. Cord prolapse (where the umbilical cord exits through the vagina before the baby) is a potential risk at time of artificial rupture of membranes and it is an obstetric emergency often requiring emergency caesarean.
4. Uterine rupture (tear in the uterus) – is uncommon with induction of labour, however, when it does occur it is life threatening to baby and mother. If uterine rupture is suspected, preparation for an emergency caesarean +/- uterine repair or hysterectomy should be made.

 

Kindly written and reviewed by Dr Allison Johns BSc (Hons) MBBS, Doctor at King Edward Memorial Hospital and Editorial Advisory Board Member of Virtual Medical Centre.

 

More information

For information on alternative and more natural methods to induce labour read Induction of Labour – Natural Methods

 

References

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