Induction of labour (IOL) refers to the use of medications to stimulate the onset of labour.
Induction of labour can be used where patients go over the due date. IOL is offered between 41 and 42 weeks gestation.
Induction of labour is also offered in situations where it is beneficial to start labour early, such as:
- Prelabour rupture of membranes
- Fetal growth restriction
- Obstetric cholestasis
- Existing diabetes
- Intrauterine fetal death
The Bishop score is a scoring system used to determine whether to induce labour.
Five things are assessed and given a score based on different criteria (minimum score is 0 and maximum is 13):
- Fetal station (scored 0 – 3)
- Cervical position (scored 0 – 2)
- Cervical dilatation (scored 0 – 3)
- Cervical effacement (scored 0 – 3)
- Cervical consistency (scored 0 – 2)
A score of 8 or more predicts a successful induction of labour. A score below this suggests cervical ripening may be required to prepare the cervix.
Options for Induction of Labour
Membrane sweep involves inserting a finger into the cervix to stimulate the cervix and begin the process of labour. It can be performed in antenatal clinic, and if successful, should produce the onset of labour within 48 hours. A membrane sweep is not considered a full method of inducing labour, and is more of an assistance before full induction of labour. It is used from 40 weeks gestation to attempt to initiate labour in women over their EDD.
Vaginal prostaglandin E2 (dinoprostone) involves inserting a gel, tablet (Prostin) or pessary (Propess) into the vagina. The pessary is similar to a tampon, and slowly releases local prostaglandins over 24 hours. This stimulates the cervix and uterus to cause the onset of labour. This is usually done in the hospital setting so that the woman can be monitored before being allowed home to await the full onset of labour.
Cervical ripening balloon (CRB) is a silicone balloon that is inserted into the cervix and gently inflated to dilate the cervix. This is used as an alternative where vaginal prostaglandins are not preferred, usually in women with a previous caesarean section, where vaginal prostaglandins have failed or multiparous women (para ≥ 3).
Artificial rupture of membranes with an oxytocin infusion can also be used to induce labour, although this would only be used where there are reasons not to use vaginal prostaglandins. It can be used to progress the induction of labour after vaginal prostaglandins have been used.
Oral mifepristone (anti-progesterone) plus misoprostol are used to induce labour where intrauterine fetal death has occurred.
There are two means for monitoring during the induction of labour.
- Cardiotocography (CTG) to assess the fetal heart rate and uterine contractions before and during induction of labour
- Bishop score before and during induction of labour to monitor the progress
Most women will give birth within 24 hours of the start of induction of labour.
The options when there is slow or no progress are:
- Further vaginal prostaglandins
- Artificial rupture of membranes and oxytocin infusion
- Cervical ripening balloon (CRB)
- Elective caesarean section
Uterine hyperstimulation is the main complication of induction of labour with vaginal prostaglandins. This is where the contraction of the uterus is prolonged and frequent, causing fetal distress and compromise.
The criteria for uterine hyperstimulation varies slightly between guidelines (always check local policies and involve experienced seniors). The two criteria often given are:
- Individual uterine contractions lasting more than 2 minutes in duration
- More than five uterine contractions every 10 minutes
Uterine hyperstimulation can lead to:
- Fetal compromise, with hypoxia and acidosis
- Emergency caesarean section
- Uterine rupture
Management of uterine hyperstimulation involves:
- Removing the vaginal prostaglandins, or stopping the oxytocin infusion
- Tocolysis with terbutaline
Last updated September 2020