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How is labour induced?
There are really two principal ways of inducing labour. One or both may be used in each case.
Prostaglandins (PGE2) are the chemicals used specifically to prime the cervix for labour. They also have an ‘oxytocic’ effect in that they stimulate the uterus and may bring about contractions.
Other related prostaglandins by the name of Misoprostol (PGE1) are increasingly in vogue for labour induction especially because of their higher versatility as they can be administered both vaginally and orally.
The second method of labour induction is that of amniotomy.
Amniotomy, simply means rupturing the membranes or "breaking the waters". Both methods are, in most cases, used with a supplemented oxytocin drip.
What do the prostaglandins do in labour induction?
During pregnancy, the cervix or ‘neck of the womb’ is firm and closed because its main function is to maintain the ever increasing size and weight of the contents inside the womb cavity. At term, before labour, the cervical function changes to facilitate smooth and safe birth.
To be able to do this, the cervix undergoes profound changes, whereby it becomes softer, thinner, shorter and distensible. These acquired characteristics allow it to open (dilate) when uterine contractions start.
Prostaglandins are used to bring about these changes to the cervix.
How are the prostaglandins administered?
The most popular method of administration is vaginal. It is mostly given in the form of a gel or vaginal pessaries.
Also available are slow-release devices, which are also inserted vaginally and can be retrieved instantly if the need arises. They are more expensive and less popular with obstetricians.
PGE1 (Misoprostol) oral tablets are also increasingly used especially for women who would prefer to avoid the vaginal route of labour induction. These are not available in every unit.
There is no place for intravenous prostaglandins in induction of labour.
What does induction using vaginal prostaglandin involve?
To begin with, a vaginal examination will be performed. This is to assess the state of the cervix and to determine whether the prostaglandins will be required and at what dosage. This will be followed by administration of the gel or pessary. This is followed by fetal monitoring for anything up to one hour, longer if necessary.
The monitoring is essential because sometimes the uterus responds abnormally to the stimulus of the prostaglandins and causes fetal distress. Monitoring is therefore an essential precaution. Fetal distress is, however, a rare complication.
How many times do prostaglandins have to be administered before the cervix is "ready'?
Most women will need one or two administrations, given four to six hours apart. In a few instances, more administrations of the gel or pessary may be required because of poor cervical response to the prostaglandins.
Rarely, no response occurs and the cervix remains obstinately unchanged. This is a failed induction.
What happens after the cervix is ready, following prostaglandin administration?
The next step will be amniotomy or ‘breaking the waters’. Once the waters are broken, uterine contractions are expected to follow. Some practitioners will start the oxytocin drip straight away after breaking the waters, while others advocate giving some time (one or two hours) to allow the uterus to start contracting spontaneously before considering the drip.