Definition and Indications

 

Induction of labour is relatively commonplace, with 20% of UK labours artificially induced. It is done when the decision is made by the obstetrician that it is safer for either mother or baby for delivery to occur imminently, rather than continue the pregnancy. This must not be confused with augmentation of labour, which augments the process once it has already begun.

 

Indications for induction of labour can be maternal or fetal:

    Membrane sweep

     

    This is a technique used to encourage spontaneous labour. During a vaginal examination, fingers are inserted between the internal os and the membranes to separate membranes from the uterine wall. This process releases endogenous prostaglandins which aid onset of spontaneous labour. This is usually performed at term, often in the antenatal clinic. Once carried out after term, this technique almost doubles the incidence of spontaneous labour. If the pregnancy persists beyond Term +10 then formal induction of labour with exogenous prostaglandins and ARM ensues. 

     

    Assessing the favouribility of the cervix

     

    The bishops score is used to assess the favouribility of the cervix for induction of labour. This evaluates the likelihood that induction will be successful; a score of 5 or more is appropriate for induction. If the score is <5 the cervix may be 'ripened' using prostaglandins. 

    Bishop's Score used to assess favourability of cervix and subsequent method of induction used

    No Prostaglandins should be given if there is already regular uterine activity.

     

    Prostaglandins cause uterine contractions which reduce uterine blood flow and compromise the fetus; monitoring using cardiotocograph (CTG) is thus a useful monitoring tool. It is for this reason that contractions should not exceed 5 in 10 minutes. 

     

    If the Bishop's Score rises above 5 at any stage during the use of PGE2's (prostaglandins)  to ripen the cervix, consider ARM

     

    Artificial Rupture of Membranes (ARM)

     

    ARM can be performed to induce labour once the cervix is favourable (Bishop's Score >5). It can also be used to augment labour if there is slow progress and membranes have not ruptured spontaneously.

     

     

    Before beginning ensure that the head is well applied to the cervix (on vaginal examination) and continuous CTG monitoring is available if indicated.

     

    Amniotomy hook

    Once the tips of index and middle fingers are in contact with membranes, and amniotomy hook is passed along the groove between two fingers (hook pointing inwards) and the hook is then pointed upwards to rupture membranes.  Ensure cord has not prolapsed before removing fingers and monitor fetal condition on CTG.

     

    Liquor is usually seen after ARM. Absence of liquor following ARM could be because of a well-engaged head or oligohydroamnios. Monitor the fetus carefully if liquor is absent.

     

    Cord prolapse is a dangerous complication of ARM, so ensure the head is well engaged before rupturing membranes.

     

    90% of mothers labour spontaneously following ARM.

     

    Syntocinon

     

    This oxytocic can be started following ARM with favourable cervix (if no spontaneous labour after 2 hours) or to augment slow, non-obstructed labour. CTG monitoring is mandatory. Infusion can only be started once membranes have ruptured.

     

    Dosing - titrated against contractions (up to a maximum of 4-5 contractions in 10 minutes).

     

    Subsequent management

     

    Manage labour as normal if it occurs.

     

    If induction fails, consider conservative management if there is no fetal distress and the indication is not time-sensitive. Caesarian section is indicated in the presence of fetal distress or if induction was performed for a significant/time-senstive indication, which is usually the case.

    Summary of the steps involved...

    References

     

    Magowan BA, Owen P & Drife M (2009). Clinical Obstetrics and Gynaecology, 2nd Edition. Saunders Elsevier.

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