Induction & Augmentation of labour
Definitions:Induction of labour: Artificial initiation of the process of labour.
Planned delivery signifies the induction of parturition, as an elective procedure, at a predetermined time.
Augmentation of labour: it is an attempt to assist or accelerate labour that had already begun normally.
Common indications for induction:
1.Post dates.
2.Small for gestational age/ IUGR.
3.Pre-eclampsia / PIH.
4.Spontaneous or premature rupture of membranes.
5.Antepartum haemorrhage.
6.Intrauterine death.
7.Diabetes mellitus.
8.Congenital fetal abnormality.
The woman & her partner should be given full advice about the risks of the induction. These are determined essentially by the parity and the cervical condition.
Depending on:
1.The history of the patient: this depends entirely on the existing condition as an indication for induction of labour, has she already had a show?, a history of normal fetal movements is reassuring, history of prelabour contractions.
2. Examination: General & abdominal exam. should be as already outlined.
Particular attention should be paid to the size of the fetus and the degree of engagement of the head.
Vaginal exam. is essential to determine the favorability of the cervix according to Bishop's score. (normally the cervix becomes shortened, softer, came forward and started to dilate. If labour is induced before this process then the induction process must be correspondingly longer).
Bishop's score:
Score 0 1 2 3
Dil.of the cx. (cm) 0 1or2 3or4 5&more
Consistency of cx. firm medium soft -
Length of cx.(cm) >2 2-1 1-0.5 <0.5
Position of cx. post. central ant. -
Station (cm) 3 2 1or0 below
Of all the parameters in the Bishop's score the dilatation of the cervix and the station of the presenting part are the most important.
The higher the score………… the easier the induction.
Treatment:
The methods of induction of labour after 37weeks most commonly include prostaglandin gel or pessaries and ARM with or without oxytocin.
The methods used depend upon the Bishop's score and the indication for induction.
It can be divided to surgical method and medical methods.
Surgical method:
Involving the use of ARM (artificial rupture of membranes) (amniotomy). It is best to avoid amniotomy after recent administration of prostaglandins because of the surge of endogenous prostaglandin which it produces, risking hypertonus. In certain high risk cases amniotomy may be beneficial to allow early internal fetal monitoring. If the Bishop's score is more than 10 it may be possible to induce labour simply by amniotomy (this is more successful in multiparous women). The colour of amniotic fluid should be checked. FH (before & after ARM) should be checked.Medical methods:
Prostaglandins are available as tablet or gel (prostaglandin E2).Prostaglandin gel is re-administered after 6 hr. and an ARM performed when the cervix starts to open. Prostaglandins can be administered orally, sublingually or intravenously, but these routes are unreliable. IV.administration is particularly problematic as prostaglandins are metabolized very quickly, therefore, high doses have to be given leading to gastrointestinal side effects.Oxytocin (syntocinon) : It is an octapeptide.It causes contraction of the myometrium and also of the myoepithelial cells of the breast. The response of the myometrium to oxytocin is relatively slight until late pregnancy when, in response to physiological doses, strong but rhythmical contractions occur. In abnormal large doses of syntocinon, it will cause sustained contraction, which can greatly reduce the placental blood flow and cause fetal hypoxia or even death. It is destroyed in the GIT so it is administered by IV.infusion. The dose is measured in milli-units (mU) per minute. (the starting dose 2mU/min, up to 32mU/min). It needs 35-40 min.to start its effect.
The use of prolonged high dose syntocinon increases the risk of neonatal hyperbilirubinaemia (may be due to osmotic swelling of erythrocytes, more easily haemolysed).
Clinical uses of oxytocin:
1.to induce labour.
2.to augment slow labour.
3.in the 3rd stage of labour.
4.during therapeutic abortion.
By adding 10units of syntocinon to 500ml of isotonic saline, one drop will contain 1mU (20drop/ml)
The woman must be under continuous supervision, by CTG (FH, ut.contraction).
Because of its antidiuretic effect, care should be taken not to administer large volume of IVF., to avoid water intoxication (major disturbance of electrolytes affecting both mother and fetus).
During induction of labour:
CTG should be performed at the start of every induction.
The stimulation of contractions should be gentle.
All staff must be aware of the need to monitor the fetus carefully during uterine stimulation, bec. of the risk of hypertonus and fetal hypoxia.
As in the management of normal labour, it is helpful to record findings on a partogram.
In case of uterine hyperstimulation(hypertonus):
There will be fetal bradycardia, so oxytocin should be switched off immediately, oxygen and IVF should be given. If the ut.contractions not resolved, tocolysis should be induced by administering a bolus dose of ritodrine or salbutamol(IV). If fetal bradycardia continues, immediate C/S should be performed.
Complications of induction of labour:
It may fail, resulting in C/S.Uterine hyperstimulation, resulting in fetal asphyxia and C/S.
Uterine rupture.
Increases incidence of assisted vaginal delivery.
Increases incidence of PPH.