Reasons for Induction of Labour
It is always nice to go into labour spontaneously. However, some women will need to be induced for medical reasons such as high blood pressure or gestational diabetes. Some will need to be induced for fetal reasons such as a small baby and / or concerns about fetal movements and placental function. The most common reason for induction is when a pregnancy goes beyond the due date. Sometimes it is appropriate to induce someone at term for practical reasons such as anxiety about a previous rapid labour, concerns about organizing child care for other children, or the availability of a partner to attend the delivery.
Post-Dates Induction of Labour
We used to think that the use-by-date of the placenta was 42 weeks as over 98% of women would deliver by this time. Women would be induced by 411/2 weeks (Term + 10 days) to provide the maximum chance of labouring spontaneously. In the 1990s there was a large study carried out by Canadian researchers where they recruited thousands of women who had reached 41 weeks gestation. They were randomized to being induced at Term+10 or letting them remain pregnant until spontaneous labour. They found that in the group that were induced at Term+10, there was less meconium liquor and there were fewer emergency Caesarean sections. So, it showed that there was no advantage in going beyond Term + 10 and that being induced did not increase the Caesarean section rate.
There has been a lot of research recently on stillbirth. We know that between 39 and 42 weeks gestation, there will be around 2 per 1000 unexplained stillbirths after the baby’s heart has stopped prior to labour. The risk of stillbirth increases the longer the pregnancy continues, so the risk is much greater after 41 weeks than it is at 39 weeks. Risk of stillbirth is increased by various factors including maternal age > 35 years, maternal infection, maternal obesity, diabetes, hypertension and smoking.
Over 60 % of these stillbirths have been associated with a maternal report of decreased fetal movements prior to fetal demise. It used to be accepted that fetal movements were less close to term. In view of the stillbirth statistics, any decrease in fetal movements is concerning as it may reflect a problem with placental function which is affecting baby’s wellbeing. Women are now offered induction of labour from 39 weeks onward due to this small risk of stillbirth.
In recent studies where groups of women at term (39 to 40 weeks) have been randomly assigned to being induced, or waiting for spontaneous labour, the proportion of outcomes are statistically similar in both groups. There are around the same number of normal vaginal deliveries, Caesarean sections or assisted vaginal births (vacuum, forceps). Going into labour spontaneously does not prevent the possibility of Caesarean section or assisted vaginal delivery as these outcomes will occur in a proportion of women labouring for the first time.
It would appear that however labour is established, whether induced or not, whatever is going to happen will happen. With any labour there is a chance that things may not progress or baby may become distressed. If there is cord entanglement or placental issues that cause fetal distress, this will happen whether induced or not. If baby’s head is not going to fit through the pelvis resulting in failure to progress in labour, this will happen whether induced or not. Assisted delivery at the pushing stage may be required, whether induced or not. A well-managed induction will not change the outcome.
Methods of Induction
The method of induction will depend on the cervix and how much the cervix has opened up prior to labour. This can range from closed to 3cm dilated or sometimes more.
If the cervix is dilated enough to admit two fingers, then it will be possible to break the waters or perform as Assisted Rupture of Membranes (ARM). If the waters break by themselves or after an ARM, it can still take hours or days for contractions to establish. ARM is combined with Syntocinon infusion to bring on the contractions.
If the cervix is still long and closed it will not be possible for an ARM and cervical ripening will be required. Cervical ripening will open up the cervix so that it is then possible to induce labour with ARM and Syntocinon.
Common methods of cervical ripening include Prostaglandin gel, Cervadil tape to deliver prostaglandin, or mechanical means such as a balloon catheter inserted through the cervix. Sometimes these methods will put women into labour but more often the only effect is ripening of the cervix.
On arrival for induction, maternal pulse, temperature, and blood pressure will be checked. A CTG will monitor baby’s heart rate for about 30 minutes. If all of the observations are reassuring, a midwife will administer the first dose of prostaglandin gel. During a vaginal examination, cervical dilatation will be checked, then a blunt syringe is used to squirt prostaglandin gel into the back of the vagina behind the cervix. Prostaglandin gel is absorbed by the collagen of the cervix and causes the cervix to soften and open.
Most of the absorption happens in the first half an hour. A CTG will monitor baby’s heart rate for 60 minutes after insertion of the gel. Rarely (<3 per 1000), there may be an exaggerated hyperstimulation effect so that the uterus will contract strongly. Baby may become distressed in these 60 minutes. Sometimes the gel has to be washed out of the vagina or medication given to relax the uterus. In less than 1 per 1000 reactions, an emergency Caesarean section may be needed for fetal distress. Hyperstimulation is more likely to occur in women who have laboured before and more likely if the cervix is significantly dilated.
The gel may cause crampy period pain. About four hours after insertion of the gel there may be a run of contractions. Sometimes this will continue and become labour or the waters may break. Usually contractions will settle but the crampy period pain will persist. Oral medication or a narcotic injection can be given if this pain is not tolerated.
The minimum time for the gel to change the cervix is six hours so the cervix will be examined again after six hours, unless labour commences. The first dose of gel is often given at night and allowed to act on the cervix for up to 12 hours before the cervix is examined. Most cervixes will respond to one dose of gel. It is possible to repeat doses after the minimum 6 hours, if the cervix has not changed enough to break the waters and there is not too much uterine activity. Rarely (<3 per 1000), the cervix may remain long and closed after three doses of gel. If the reason for induction is not urgent, there is an option to wait 24 hours and repeat the course of gel. Change to the cervix may occur during this second course. A slow response to prostaglandin gel can be associated with poor progress in labour, or fetal distress in labour, resulting in Caesarean section. After 3 doses of gel, if the cervix has not changed, many women will opt for a Caesarean section rather than persist with cervical ripening.
The process for Cervidil tape is similar. At vaginal examination the part of the tape containing the prostaglandin is tucked behind the cervix and the other end of the tape is left hanging out of the vagina. Unlike the gel which is absorbed all at once, Cervidil releases a controlled amount of prostaglandin over the whole time it is in place. Cervidil can be left in place for up to 24 hours so there may be fewer vaginal examinations than with multiple doses of gel. Hyperstimulation is less likely because of the controlled release but if it occurs the Cervidil can be easily removed by pulling on the tape.
A balloon catheter can be used if prostaglandin needs to be avoided or if prostaglandin was unsuccessful at ripening the cervix. The balloon catheter can be threaded through the cervix at vaginal examination or under vision at a speculum examination. When the balloon is inflated this puts mechanical pressure on the cervix to open up. Some balloon catheters are designed to have two balloons that can be inflated above and below the cervix. Insertion of the catheter may be more uncomfortable than use of gel or tape. There may be more of a requirement for analgesia because of more period pain generated by pressure on the cervix.
Syntocinon Induction of Labour
Once the membranes have ruptured (spontaneously or assisted), contractions can be started or improved by the use of a synthetic oxytocin (Syntocinon) infusion. Syntocinon is the same polypeptide as oxytocin that is produced by the pituitary and goes into the bloodstream to reach the receptors in the uterine wall to cause contractions. Syntocinon infusion is started at very low levels and gradually increased to mimic what would occur physiologically. Most women will not notice a significant increase in uterine activity for several hours after commencement of the Syntocinon infusion, but some may start contracting sooner.
Some people think that Syntocinon induction of labour makes labour more painful and intense. It may be more intense in the sense that the process is more efficient. With Syntocinon, the time taken for regular contractions to result in full dilatation can be decreased by several hours compared to contractions without Syntocinon. It is not possible to make the uterine muscle contract harder than it is capable of, for any one contraction. Labour may feel more intense because the aim is to make every contraction as efficient has it can be. There is no doubt that women are more likely to opt for pain relief than those that labour spontaneously, due to this sense of intensity.
First labours may involve starting and stopping of contractions. There may be 30 minutes of regular contractions followed by 30 minutes of occasional contractions. With Syntocinon induction of contractions the aim is to eliminate periods of time when the uterus is not contracting efficiently. Similarly, if a uterus is contracting 3 times in 10 minutes without Syntocinon, there may be one huge contraction which is doing all the work followed by two smaller contractions. These less intense contractions are not adding much to propelling baby downward or to dilating the cervix.
The use of Syntocinon can make the uterine muscle contract in a more coordinated way which also increases efficiency of each contraction. Sometimes it is possible for a uterus to be contracting spontaneously and regularly but there is no progress in cervical dilatation. It is known that when a Syntocinon infusion is used to augment the contractions, this will result in progress of cervical dilation. The additional Syntocinon molecules act on the receptors in the uterine muscle to make the contraction more coordinated so that there is more of an expulsive effort from the top of the uterus toward the cervix.
With Syntocinon induction the aim is for the uterus to contract 4 times in 10 minutes with each contraction being palpated as moderate to strong. Every 30 minutes the midwife will check the frequency and strength of the contractions by palpating the abdomen. If the contractions are insufficient the Syntocinon infusion can be increased and if there are too many contractions the Syntocinon infusion can be decreased or discontinued. The effect of the Syntcocin disappears a few minutes after the infusion is discontinued.
When the uterus is contracting with a Syntocinon infusion, the fetal heart needs to be monitored continuously. Sometimes the first indication that there are too many contractions will be a certain pattern of fetal heart rate on the CTG. Wireless monitoring can occur with one belt around the abdomen keeping the monitor on the fetal heart, so that it is possible to move around the room and not be confined to bed. Sometimes wireless monitoring is good enough to sit on the fit ball in the shower and still be monitored. Sometimes if the abdominal belt is not providing good monitoring, then it is possible to have wireless monitoring with the fetal scalp electrode. This is a fine wire about the thickness of a hair that is attached to the outer layer of the fetal scalp at the time of an internal examination. As the fetal scalp electrode is a direct attachment to the fetus, it is a more accurate way of monitoring the fetal heart continuously.
With any labour, whether induced or not, there is a small chance that baby may become distressed or dilatation of the cervix may not progress. A well-managed induction with Syntocinon will not change the outcome. If fetal distress is going to occur (due to cord entanglement or placental issues) or progress is arrested because the head is not descending through the bony pelvis to cause dilatation of the cervix, this will occur regardless of whether contractions establish spontaneously or whether they are augmented with Syntocinon.