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Induction of labour in obese pregnancies


  • Induction of labour (IOL) involves artificially stimulating the onset of labour through chemical and/or mechanical methods, with the aim of achieving a vaginal delivery, prior to the onset of spontaneous labour.

  • Approximately 33.0% of deliveries in the United Kingdom (UK) in 2019–20 were induced, whereas data from the Centres for Disease Control and Prevention demonstrated that 29.4% of deliveries in the United States (US) in 2019 were induced. These figures have increased over the last decade where in the UK, only one in five women had IOL in 2009–10.

  • Induction of labour is offered when continuing with the pregnancy confers more risks to the mother and/or the foetus than delivery. There are various clinical indications which support IOL including maternal diabetes, preeclampsia and hypertension, as well as foetal growth restriction, to name a few.

  • One of the key indications for IOL is to prevent prolonged pregnancy which has been shown to be associated with increased perinatal morbidity and mortality.

  • Data from the Cochrane Database suggest IOL at or beyond 37 weeks’ gestation in ‘low-risk’ pregnancies associates with a reduction in perinatal deaths, stillbirths, and neonatal intensive care admissions.

  • Additionally, there is a modest reduction in caesarean section rates in the induction of labour group compared to expectant management, with no evidence of differences in the rate of instrumental deliveries.

  • The National Institute for Health and Care Excellence (NICE) in the UK as well as the Society of Obstetricians and Gynaecologists of Canada suggest that women with ‘uncomplicated pregnancies should usually be offered induction of labour between 41 +0 and 42 +0 weeks’.

  • Regular antenatal assessments with twice-a-week amniotic fluid volume measurements and ‘nonstress test’ with cardiotocography should be offered to women who choose to delay induction.

  • The American College of Obstetrics and Gynaecology (ACOG), on the other hand, have suggested IOL may be considered at 41 +0 to 42 +0 weeks’ gestation and should be recommended beyond 42 +0 weeks’ gestation.

  • Given the global increase in obese pregnant women, it is crucial to have clear guidance on IOL in this group of women. However, there remains a lack of consensus in optimum gestation for IOL and choice of induction agents. Nevertheless, this chapter aims to collate the available information to aid in decision-making with respect to induction of labour in obese women.

39.1

Indications of induction of labour

  • 1.

    Postdates pregnancy

    • Denison et al. have demonstrated that maternal obesity is associated with a reduced likelihood of spontaneous onset of labour and greater risk of postdates pregnancies.

    • Maternal obesity during pregnancy is also associated with an increased risk of complications including maternal diabetes and preeclampsia, which may in themselves warrant earlier delivery.

    • This is reflected in an increased risk of induction of labour among obese pregnancies (odds ratio 1.70, 99% confidence interval 1.64–1.76).

    • In general, IOL among obese pregnant women with prolonged pregnancy is considered safe with no difference in Apgar scores and cord blood pH between obese and lean pregnancies.

    • However, it has also been reported that the likelihood of vaginal delivery following IOL in obese pregnant women is reduced when compared to those with normal body weight (rate of unassisted vaginal delivery in obese vs lean pregnancies, 55.0% vs 57.9%).

    • Obese pregnancies are associated with an increased risk of delivery by caesarean section (rate of caesarean section delivery in obese vs lean pregnancies, 28.5% vs 18.9%, P <.001) and prolonged second stage of labour.

    • Interestingly, when compared to IOL, elective caesarean sections in obese pregnant women have not been shown to improve maternal and neonatal outcomes, further supporting IOL as a safe and reasonable intervention for obese pregnancies.

  • 2.

    Diabetes, including gestational diabetes and preexisting diabetes

    • Both gestational diabetes mellitus (GDM) and preexisting diabetes is more common among obese pregnant women, and associated with an increased risk of maternal and foetal morbidity and mortality.

    • Delivery between before 39 +0 weeks’ gestation is recommended in women with preexisting type 1 or 2 diabetes, whereas those with uncomplicated GDM should be offered delivery before 40 +0 weeks’ gestation.

    • Both NICE and ACOG have suggested that the mode of delivery should be determined by maternal diabetic control and foetal well-being.

  • 3.

    Hypertensive disorders of pregnancy, including preeclampsia

    • Maternal obesity is associated with a higher incidence of preexisting hypertensive disorders, pregnancy-induced hypertension and preeclampsia.

    • Early delivery is commonly indicated in cases where there is evidence of maternal and/or foetal deterioration.

    • Further, results from the HYPITAT trial indicated that induction of labour in women with pregnancy-induced hypertension and mild preeclampsia was associated with a lower composite risk for poor maternal outcome secondary to progression of the disease.

    • While this study did not perform a subgroup analysis for obese pregnant women, there is evidence suggesting that obese pregnant women with preeclampsia are less likely to progress to a vaginal delivery following IOL.

    • The decision with regards to mode of delivery in this cohort of patients therefore requires a personalised and multidisciplinary approach.

  • 4.

    Foetal macrosomia

    • While maternal obesity, with or without concurrent diabetes, associates with an increased risk of foetal macrosomia and shoulder dystocia.

    • However, prediction of large-for-gestational age or foetal macrosomia during the antenatal period remains challenging due to inaccuracies with symphyseal-fundal height measurements in obese pregnant women.

    • Ultrasound assessment of estimated foetal weight during the third trimester is also subject to a degree of variability and increased maternal adiposity can impact on the quality of the images – thus resulting in inaccurate measurements.

    • A Cochrane review on induction of labour in pregnancies with suspected foetal macrosomia did not demonstrate a clear role of IOL at or near term in reducing the risk of brachial plexus injuries.

    • Therefore, in the absence of other risk factors, IOL for suspected foetal macrosomia in obese pregnancies should be considered with caution.

  • 5.

    Elective induction of labour

    • The risk of stillbirth is greater in pregnancies affected by maternal obesity and there appears to be a linear relationship between risk of stillbirth and advancing gestation in obese pregnancies.

    • Crucially, there is evidence that elective IOL in obese pregnancies may improve neonatal outcomes without increasing maternal morbidity.

    • Indeed, the Royal College of Obstetricians and Gynaecologists (RCOG) has recommended that while maternal obesity in itself is not an indication for elective IOL, it should still be considered and discussed on an individual basis.

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