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Induction of labour is medical intervention performed that stimulates the onset of labour pains
The exact mechanisms causing labour in pregnant mothers are uncertain. However, it is very likely that there is a series of events involving various hormones, genes and other substances within your body, resulting in the dual process of contractions in the womb and opening of the neck of the womb (cervix). It is also believed that this is initiated by the baby and the placenta.
You may have heard this term many times, but do you know what it means? Induction of labour (IOL) is any medical intervention performed that stimulates the onset of labour pains (i.e. to establish labour), aiming to result in the delivery of the baby vaginally (read
the article on Stages of Labour).
A variety of medical conditions may arise during the course of your pregnancy that may put you or your baby’s wellbeing at risk. This may necessitate your doctor offering you an early delivery of your baby. In certain instances where you or your baby is assessed to be unable to tolerate the stress of labour, a
cesarean section may be suggested to expedite your delivery instead. Only if time permits and there is no immediate danger to you or your baby, can an IOL be offered.
These can be broadly categorised into conditions that can put either you or your baby at risk should the pregnancy be allowed to progress. Under such a circumstance, your doctor would have investigated you thoroughly and assessed that it would be safer for either mother or baby that the delivery occurs before your due date or in rarer cases, even before maturity is reached.
It is important to note that routine IOL in uncomplicated pregnancies has not been successful in reducing stillbirth rate and results in higher rates of
forceps, vacuum and cesarean deliveries.
As with any procedure, there are certain concerns associated with an IOL. They include:
As such, an IOL is only performed when the benefits of a delivery outweigh the above-mentioned risks or when your obstetrician is confident that the risks associated with IOL can be adequately minimised by appropriate precautionary measures.
IOL is not performed when you are deemed unsuitable for a vaginal delivery in the first place. They include conditions such as a low-lying placenta, breech or transverse lie of the baby.
If you have had one previous cesarean section, an IOL is generally not advised as the risk of a uterine rupture is approximately 2.5%. This is five times higher than the risk of uterine rupture should you go into spontaneous labour on your own, and is considered to be unacceptable by many.
Labour starts when the cervix initially soften, shortens and dilates (read
the article on Labour Pain Relief). This can be achieved through the insertion of prostaglandin, a hormone, into the vagina. Locally, the pessary known as Prostin is commonly used. Once the cervix is adequately dilated and effaced (thinned out), the membranes can be ruptured and an oxytocin infusion (another hormone) can be started to maintain the labour contractions.
Prostaglandin causes softening of the cervix (neck of womb) through a disaggregation of collagen fibers in the cervix. In addition, prostaglandin stimulates uterine muscle activity leading to labor. It is administered vaginally and may be in gel or pessary. Prostaglandin induces the onset of painful uterine contractions which may lead to the opening of the softened cervix. Once the prostaglandin is inserted, the patient is required to stay in hospital for monitoring. The frequency of uterine activity and baby’s heart rate pattern are observed.
Women respond differently in terms of speed. The lowest dose regime is commonly employed to prevent over-stimulation. The patient with a favourable cervix has a better chance of responding more quickly. A favorable cervix (determined by the doctor by vaginal examination) is soft, effaced (thin), dilated, faces to the front, with the baby’s head well applied and low in pelvis. Some patients may respond with establishment of regular labour pains within six hours; while others may take up to 2–3 days.
Once the cervix is favorable, the doctor may rupture your membranes (ROM) followed by administering an oxytocin infusion. Rupturing of membranes involves using an amniohook (specially designed instrument) to break the waterbag. ROM alone will induce painful contractions in a proportion of patients. The frequencies of contractions are monitored in the delivery suite and if this is inadequate, an infusion of oxytocin is given to the blood stream via an intravenous drip.
Oxytocin is a naturally occurring hormone produced by the brain that stimulates the womb. This aims to keep the contraction frequency to about four in every 10 minutes. Unlike prostaglandin, oxytocin infusion can be stopped by switching off the infusion. As oxytocin has a short half-life in the mother’s blood, the concentration reduces rapidly and this averts potential over-stimulation.
This is not necessarily true. Some patients may experience mild pain while the cervix is responding slowly to the prostaglandin. In this instance, she is encouraged to ambulate.
There is no scientific evidence to support this myth. One reason for this perception is that a successful IOL will bring on the labour pains. The inevitable negative association leads to the negative perception.
There is nothing unnatural about going through a labour brought about by an IOL. Once labour is established (read
the article on Stages of Labour), the same rules on progress of labour apply.
Source: Dr TAN Thiam Chye, Dr TAN Kim Teng, Dr TAN Heng Hao, Dr TEE Chee Seng John, The New Art and Science of Pregnancy and Childbirth, World Scientific 2008.
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This article was last reviewed on
Monday, July 5, 2021
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