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Obstetrics Simplified - Diaa M. EI-Mowafi

Induction of Labour

Definition

It is artificial initiation of labour after viability of the foetus i.e. after 28 weeks.

Indications

Maternal

  • Hypertensive disorders with pregnancy:
    • Severe pre-eclampsia.     
    • Imminent eclampsia.        
    • Eclampsia.
    • Essential hypertension.    
    • Chronic nephritis.
  • Antepartum haemorrhage:
    • Placenta praevia type I&II.
    • Accidental haemorrhage.
  • Diabetes mellitus:
    • To avoid intrauterine foetal death and dystocia due to macrosomia.

Foetal

  • Post-term pregnancy.
  • Intrauterine growth retardation.
  • Intrauterine foetal death.
  • Rh-isoimmunization.
  • Gross congenital anomalies.

Modified Bishop Score

This score is predicting for the succession of induction of labour. The total score is in the range of 0-13, a score of 9 or more is favourable for successful induction.

  0 1 2 3
Dilatation of cervix (cm) 0 1-2 3-4 ≥5
Consistency of cervix Firm Medium Soft  
Length of cervical canal (cm) >2 2-1 1-0.5 <0.5
Position of cervix Posterior Central Anterior  
Station (cm above ischial spines) 3 2 1or 0 Below

Methods of Induction

Conservative method

It is suitable to begin with it the trials for induction of labour and consists of:

  • Stripping of the membranes: by introducing the index or the middle finger into the cervical canal to separate the membranes from the lower uterine segment all around as much as possible. This stimulates natural prostaglandin production.
  • Castor oil every 12 hours.

In most of the cases with favourable Bishop score labour is commenced within 24 hours.

Advantages:

  • Minimal cost.
  • No side effects, complications or contraindications as regard the mother or the foetus.
  • Spontaneous uterine contractions start without medication or surgical interference.
  • No rupture of the membranes so infection is minimised.
  • The procedure can be repeated for unlimited times and caesarean section must not be the alternative if it fails.

Prostaglandins

They induce ripening of the cervix and uterine contractions.

Prostaglandins can be administered via many routes (see ecbolics) but the commonest are:

  • In living foetus:
    • Prostaglandin E2 vaginal tablet 3 mg (Prostin) is applied deep in the posterior fornix. A second tablet is applied 6-8 hours later if labour is not commenced. The maximum dose is 6 mg.
    • Vaginal gel (PGE2 1-2 mg) may be more reliable.
  • In dead foetus:
    • Extra-amniotic and intra-amniotic prostaglandin F2α.

Extra-amniotic normal saline

A Foley’s catheter is passed extra-amniotically through the cervix and inflated with 10 ml of distilled water to be self retained . A drip of normal saline is connected to it to pass extra-amniotic in a rate of 1 ml/minute.

Artificial rupture of membranes (amniotomy)

Mode of action:

  • Release of prostaglandins.
  • Bringing the presenting part closer to the lower uterine segment so the uterine activity will be reflexly encouraged.

Methods:

  • Forewater (low) amniotomy: Stripping of the membranes is done first, then the forewater is ruptured by amnihook, toothed forceps or Kocher's forceps.
  • Hindwater (high) amniotomy: The Drew-Smythe catheter is introduced between the membranes and uterine wall to a point above the presenting part.

Disadvantages:

  • Less efficient in inducing labour.
  • More incidence of uterine trauma.
  • Separation of a posteriorly situated placenta.
  • Higher incidence of infection.

Amniotomy alone results in delivery within 24 hours in about two-thirds of cases.

It is now a common practice to administer oxytocics at the time of or soon after, amniotomy to shorten the latent phase. The majority of deliveries then occur within 12 hours.

Oxytocin

Mode of action: It depolarises cell membrane potential and alter permeability to sodium. The maximal sensitivity to oxytocin is achieved by 34-36 weeks’ gestation.

Method of administration: The initial rate of administration is 6 m units/ minute, increased by 6 m units/ minute every 15 minutes up to a maximum of 36 m units/minute or until 3 contractions/ 10 minutes are achieved.

Practically, this is done by putting 5 units of syntocinone in 500 ml of 5% glucose and start the IV drip by 10 drops/min. to be increased by 10 drops/ min. every 15 min. up to a maximum of 60 drops/min.

The oxytocin drip is continued through out the second, third and fourth stage of labour to guard against postpartum haemorrhage.

Hazards of oxytocin: (see ecbolics).

Failed induction of labour → caesarean section.

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