Labour induction: why and how does it work?

At 41 weeks and 6 days of amenorrhoea, it is recommended to induce labour. 

Induction from 41 weeks of amenorrhoea is possible provided the cervix is favourable (it generally results from an inability to carry out regular monitoring, a request from the expectant mother, or the need to organise care). 

Premature rupture of membranes can create a risk of infection. If cervical conditions are favourable, induction of labour may be carried out. The risk of infection increases with the duration of exposure, which is why induction should not be delayed beyond 48 hours; if delivery has not occurred within 12 hours, the recommendation is to place the pregnant woman on antibiotic prophylaxis. 

In the case of twin pregnancies, there is an increased risk of perinatal mortality once 39 weeks of amenorrhoea have passed. Induction of labour is not carried out routinely, but it is recommended not to go beyond 39 weeks + 6 days of amenorrhoea. 

Regarding diabetes, if it is poorly controlled or if there is foetal impact, labour induction may be carried out at 38 weeks of amenorrhoea + 6 days. However, if it is well controlled and there is no foetal impact, there is no justification for artificial induction. 

For babies weighing more than 4 kg (foetal macrosomia), no data supports the claim that inducing labour reduces maternal and neonatal morbidity [3]. 

In cases of intrauterine growth restriction at term, the available data do not allow for certainty regarding the benefit/risk balance of inducing labour. Growth arrest is, however, associated with high perinatal risk, which may lead to induction or a caesarean section. 

For women who have previously had a rapid labour, induction of labour from 39 weeks of amenorrhoea may be considered, provided the cervix is favourable.  

Finally, isolated arterial hypertension, hyperuricaemia, or proteinuria are not determining factors for the induction of labour. However, pre-eclampsia is a determining factor and leads to induction of labour or a caesarean section. 

In a review of 44 studies, they examined the effect of membrane sweeping on the onset of labour [5].  

Women who have had a membrane sweep are, on average, 1.2 times more likely to experience a spontaneous onset of labour compared to women who have not. It is also observed that a membrane sweep reduces the likelihood of requiring an induction of labour by an average of 27%. However, the level of evidence from studies is fairly weak, and other studies show that a membrane sweep does not influence the probability of not having given birth by 41 weeks of pregnancy and does not reduce the risk of requiring an induction of labour thereafter [6]. 

It is possible that membrane sweeping, but not cervical massage, increases the risk of membrane rupture before labour. One study [7] observed that the risk was 9% with membrane sweeping versus 0% without, and another study [8] showed that this risk was 38% with sweeping compared to 26% in the absence of intervention. 

Pain during vaginal examination and other side effects are more frequently reported by women who have had a membrane sweep [9]. 

A randomised study of more than 700 women [10], who either had a membrane sweep or no intervention, showed that the sweep increased the risk of vaginal bleeding sixfold! 

They also studied the pain associated with this procedure, and found that 31% of women said it was not painful, 51% said it was somewhat painful, and 17% said it was painful or very painful. 

When oxytocin inductions were compared with expectant management, oxytocin was found to reduce the failure to achieve vaginal birth within 24 hours (8.4% failed to give birth within 24 hours with oxytocin, compared with 53.8%).

Women in the oxytocin group were less likely to receive antibiotics, with a 31% reduction in risk. Neonatal infection had a 35% reduced risk with oxytocin induction compared with a wait-and-see management policy (1.5% versus 2.4%). The use of neonatal antibiotics was slightly lower in the oxytocin group, but the data were not statistically significant (6.2% versus 10.4%). There was no evidence of a difference between groups in rates of neonatal jaundice, respiratory distress syndrome, or Apgar score below seven at one minute. Apgar scores below seven at five minutes were similar between babies of women who received oxytocin and those who waited. Admissions to the neonatal intensive care unit did not differ between the two groups. 

High-dose oxytocin protocols tend to lead to more foetal distress. The most significant risks are hyperstimulation (common but generally brief and well tolerated), failed induction (occasional but significant) and uterine rupture in some studies (rare but serious) [13].

The previous review on oxytocin shows that the use of an epidural increases when oxytocin alone was compared with expectant management or no treatment (45.3% vs 40.9%).

The caesarean section rate also shows a small but statistically significant increase for women in the oxytocin group (10.4% compared with 9.0%).

A review that included 39 studies involving nearly 7,000 pregnant women examined the effect of PGE2 prostaglandins on labour, compared with women who received no treatment or a placebo [16]. The risk of the cervix remaining unchanged or unfavourable after 12 to 24 hours is reduced with the use of vaginal prostaglandins compared to placebo (18.9% vs 40.5%). They found that a greater number of women gave birth within 24 hours with vaginal PGE2 compared to expectant management (up to 42 weeks of gestation) (88% of the PGE2 group vs 0% of the expectant management group gave birth after 24 hours).

​​No difference between the prostaglandin group and the waiting or placebo group was found with regard to an Apgar score below seven at five minutes (2.2% vs 1.7%) or admission to a neonatal intensive care unit (8.8% vs 9.4%).

The caesarean rate is lower in the PGE2 groups compared to the placebo group or the expectant management group (13.5% versus 14.8%). 

Prostaglandins may increase uterine hyperstimulation with changes in foetal heart rate [17]. These data are confirmed by the review on prostaglandins, which shows uterine hyperstimulation accompanied by changes in foetal heart rate in association with vaginal PGE2 compared to placebo (4.8% vs 1.0%).

Labour can be induced with two hormones: dinoprostone, also known as PG2, and misoprostol. Misoprostol appears to be associated with a tenfold increase in the risk of uterine rupture [18]. It should be noted that induction with prostaglandin gel is rare in France.

Compared with vaginal PGE2, oxytocin was more likely to result in an unfavourable or unchanged cervix between 12 and 24 hours (23.8% vs 9.2%). They also observed that oxytocin had tripled the number of unsuccessful vaginal deliveries within 24 hours compared with prostaglandins (70% vs 21%). 

Women receiving oxytocin were more likely to have an epidural compared with women who received prostaglandins (52.8% versus 48.4%). 

Rates of chorioamnionitis (intra-uterine inflammation) were lower when oxytocin was compared with vaginal PGE2 (3.9% vs 6.0%). The use of neonatal antibiotics was also lower in the oxytocin group (7.3% vs 10.9%). 

Another study showed that in cases of premature rupture of membranes, labour induction with oxytocin led to fewer maternal infections than awaiting spontaneous labour or induction with prostaglandins [20].

Indeed, a full bladder can create an obstruction and prevent the baby's head from pressing against the cervix).

Repositioning the mother or encouraging her to move if she is able to, as this can help mobilise the pelvis and encourage the baby's engagement. 

Of course, there are also a few methods worth trying. 

Acupuncture, which allows the cervix to relax followed by very rapid dilation after rebalancing energy. It is an effective method for encouraging a natural birth. 

To find out more about this topic, read our article: acupuncture pregnancy.

The witch's thread massage, which allows the cervix to relax and dilation to resume. It involves massaging specific points on the cervix: the four cardinal points and the point located at the 11 o'clock position.

Managing pain and anxiety is important, as these factors can make things worse [24].