Historically, elective induction has been discouraged due to the associated increased risk of caesarean birth and adverse birth outcomes compared with spontaneous labour. However, the recent ARRIVE trial demonstrated that elective induction at 39 weeks of gestation among low-risk, first-time mums was associated with reduced caesarean rates. Women are weighing up the advantages and disadvantages of induction at an alarmingly high rate and the pressure and burden of the decision is overwhelming and stressful. So, what does the research say?

There are several key studies being referenced in the induction landscape. These are The Big Baby Trial, The ARRIVE Trial, The SWEPIS Study, the INDEX study and the 35/39 trial. An Australian meta-analysis has also been influential in current induction discussions. The ARRIVE Trial examined labour induction versus expectant management of low-risk nulliparous women and is arguably the most influential piece of research being cited in support of the induction of labour at 39 weeks. It aimed to ‘unmuddy’ the waters about labour induction, particularly at 39 weeks. The findings showed no significant difference in the primary perinatal outcomes of the mother or the baby, but it did find a significant difference in the caesarean rate with the women being induced at 39 weeks requiring fewer caesarean sections than the expectant management group. The results were ultimately in opposition to much of the previous research and so have perhaps not cleared the waters at all.

The 35/39 trial looked at induction of mothers who were aged 35 years and older at 39 weeks pregnant. The average age of women at childbirth in high-income nations has been increasing steadily for approximately 30 years. While the age of women bearing children is increasing, women over the age of 35 do have increased risks of perinatal death, hypertensive disease, gestational diabetes, placenta previa and placental abruption. Women in this age group also have a higher risk of preterm labour, antepartum stillbirth and of birthing babies with higher or lower birth weights. Predictably, women in this age group are experiencing higher rates of obstetric intervention when compared to younger women. The study concluded that induction of labour at 39 weeks has no statistically significant impact on the caesarean section rate. Furthermore, maternal and neonatal outcomes didn’t differ significantly between the two groups. However, the rate of assisted vaginal deliveries was higher in the induction group, although not statistically significant.

The Big Baby Trial investigated the induction of labour as a preventative measure against shoulder dystocia in babies suspected to be large. Shoulder dystocia is an obstetric emergency defined as a vaginal cephalic birth that requires additional obstetric manoeuvres to deliver the baby after the head has been delivered. Potential complications of shoulder dystocia include maternal haemorrhage and third-degree and fourth-degree perineal tears and psychological trauma. For the baby, complications include fractures, brachial plexus injury, hypoxic ischaemic encephalopathy, and neonatal death. Macrosomia (variably defined as fetal weight of more than 4.0 kg or more than 4.5 kg) and the fetus being large for gestational age (LGA; >90th percentile) is associated with an increased risk of shoulder dystocia. The Big Baby Trial found no significant difference in the incidence of shoulder dystocia between the two trial groups and no significant difference in neonatal morbidity. Interestingly, only 42% of the ‘suspected big babies’ were actually big.

A 2022 Australian meta-analysis of induction of labour at 39 weeks vs expectant management explored the labour-related complications, such as perineal trauma and postpartum haemorrhage, and neonatal outcomes of both options. The review of 1.6 million women across 14 studies found that induction of labour at 39 weeks of gestation compared with expectant management was associated with improved labour-related outcomes, including a 37% reduction in perineal injury risk. The findings suggest that elective induction of labour at 39 weeks of gestation is likely to be safe and beneficial for some women. However, this was not necessarily the case for nulliparous women who saw an increase in shoulder dystocia.

The above studies do present some valid results in favour of induction at 39 weeks, however, each of the studies have flaws in randomization, participant factors and several of them showed no significant difference between induction and expectant management groups across certain primary or secondary outcomes. Furthermore, we are still lacking any research exploring the long-term implications of these inductions on the mothers or the babies. Additionally, research conducted into women’s reflections upon their inductions found that birth trauma increased for women who were induced and that women overwhelmingly desired to avoid induction.

The obstetric management of women with a pregnancy exceeding 41 weeks varies considerably between and within countries. Although induction at 41 weeks has now become an accepted policy in many countries, in some others no consensus exists on the timing of induction in late-term pregnancy. Post-term pregnancy is a pregnancy extended to or beyond 42 weeks and is associated with increased perinatal morbidity. The World Health Organization and various guidelines throughout the world therefore recommend induction of labour after 42 weeks.

The INDEX Trial, which investigated the induction of labour at 41 weeks vs expectant management until 42 weeks, found no significant difference in combined secondary perinatal outcomes and no significant difference in caesarean rates. The SWEPIS study explored induction at 41 weeks with expectant management and induction at 42 weeks and it found no significant difference in primary composite adverse perinatal outcomes. However, the study was terminated early due to perinatal mortality and results could not be interpreted accurately. Many providers will cite the increased risk of stillbirth as gestational age increases. However, whilst this is factual information, it is important to consider how this information is presented. For example, many women are told that their chances of experiencing stillbirth doubles for each week of pregnancy past 37 weeks. While this is accurate, it does not truly inform the woman of the statistics and is worded as more of a scare tactic. A woman’s chance of stillbirth is 1 in 10,000 at 37 weeks, 2 in 10,000 at 38 weeks and so on and so forth. This presentation of the statistics may be much less confronting and deemed less risky to a woman than being told the chance doubles.