Introduction

The worldwide prevalence of obesity has doubled in the last 30 years, with approximately 300 million females above the age of 20 years categorised as overweight (body mass index (BMI) between 25.0 and 29.9 kg/m ² ) or heavier (BMI >30 kg/m ² ) . Obese pregnant women not only pose a challenge during their antenatal care but are also at considerable risk during their labour and delivery. A number of observational studies have shown a higher incidence of intrapartum and post-partum complications among obese women, compared to those with a normal BMI .

Preparation for labour is of vital importance and involves a multidisciplinary approach to the obese woman’s antenatal care. The place of delivery (for example, a tertiary institution) is a key factor to consider. Caring for the obese parturient and the associated challenges place increased demands on staff and resources across maternity and delivery wards, operating theatres and neonatal units . Awareness of risks and up-to-date evidence-based clinical practice are essential in ensuring safe outcomes and cost-effective utilisation of resources.

Preterm birth

Preterm birth is associated with significant neonatal mortality, morbidity and long-term disability . Obesity increases the risk of iatrogenic preterm delivery related to co-morbidities such as pre-eclampsia and gestational diabetes . The evidence is not so clear with regard to the risk of spontaneous preterm delivery in obese women. Whilst there is an increased risk of preterm delivery, mostly due to associated co-morbidities, they are iatrogenic, rather than due to the spontaneous onset of labour . Spontaneous onset of labour in obese women has been shown to be associated with an increased risk of premature pre-labour rupture of membranes (PPROM) . The mechanism behind this is hypothesised to be related to the up-regulation of inflammatory cytokines and the increased risks of genital and urinary tract infections predisposing to chorioamnionitis in obese women.

Preterm birth

Preterm birth is associated with significant neonatal mortality, morbidity and long-term disability . Obesity increases the risk of iatrogenic preterm delivery related to co-morbidities such as pre-eclampsia and gestational diabetes . The evidence is not so clear with regard to the risk of spontaneous preterm delivery in obese women. Whilst there is an increased risk of preterm delivery, mostly due to associated co-morbidities, they are iatrogenic, rather than due to the spontaneous onset of labour . Spontaneous onset of labour in obese women has been shown to be associated with an increased risk of premature pre-labour rupture of membranes (PPROM) . The mechanism behind this is hypothesised to be related to the up-regulation of inflammatory cytokines and the increased risks of genital and urinary tract infections predisposing to chorioamnionitis in obese women.

Post-term pregnancy

A progressive relationship between increasing BMI and prolonged gestation was demonstrated in a retrospective study of 9336 births. Higher pre-pregnancy BMI was associated with a higher risk of pregnancy progressing past 40 weeks of gestation, with 28.5% of obese women progressing beyond 41 weeks of gestation, compared with 21.9% of normal-weight women ( P < 0.001). Obese women also had an increased risk of reaching 42 weeks of gestation compared with women of normal pre-pregnancy BMI, with an adjusted odds ratio (OR) of 1.69 (95% confidence interval (CI), 1.23–2.31) ( Fig. 1 ) .

Survival curves for BMI categories, with delivery as the failure event, P < 0.001 for log-rank test. Reprinted from Am J Obstet Gynaecol, Vol 197 edition 378, Stotland, N. E., Washington, A. E., and Caughey, A. B. Prepregnancy body mass index and the length of gestation at term. e1–378.e5 with permission from Elsevier.

Similar results have been found in other large population-based observational studies . The results are significant even considering the vast number of obese women who are delivered electively, either by induction of labour (IOL) or by elective caesarean section, before they reach 40 weeks or beyond, leading to an increased need for IOL for post-dates pregnancies ( Table 1 ) .

The mechanism behind the prolongation of gestation in obese women is unclear. Some authors have postulated that endocrine factors, which may have a role in the initiation of labour, are altered in obese women due to an excess of hormonally active adipose tissue .

Preparation prior to labour

The antenatal care of an obese pregnant woman involves preparation of the woman, staff and family for the intrapartum and post-partum periods. Accurate documentation of weight at the booking visit is essential and a reweighing in the third trimester of morbidly obese women is important for planning for manual handling equipment. The guidelines for the management of obese women in pregnancy from the United Kingdom recommend that women with a booking BMI of ≥30 kg/m ² have an informed discussion about possible intrapartum complications and their management with a consultant obstetrician, which is documented in the antenatal notes. The multidisciplinary approach involves not only good obstetric and midwifery care but also careful screening of co-morbidities such as gestational diabetes and hypertensive complications, dietary advice and review by the specialist obstetric anaesthetist to identify potential difficulties during the intrapartum period. Manual handling assessment in the third trimester using validated scoring tools are helpful for planning prior to admission to hospital. These antenatal preparations, although resource intense, ensure effective communication between staff involved in her care as well as keeping the woman well informed, minimising the chances of adverse outcomes .

Induction of labour

There is little data on the outcomes of IOL in the obese woman in the preterm setting. Several large studies have shown a relationship between obesity and an increased incidence of IOL . IOL is required more often due to both the strong association of medical co-morbidities with obesity, such as diabetes mellitus and hypertension, and the increased rates of post-term pregnancies seen in obese women. Even when the presence of pre-eclampsia is adjusted for, compared with normal-weight women, morbidly obese women are more likely to be induced, with an adjusted OR of 2.38 (95% CI 2.17–2.60) .

Arrowsmith et al., in a retrospective cohort study of 29,224 women, found that higher maternal BMI at booking was associated with an increased risk of prolonged pregnancy and IOL, and 8497 women (29.1%) had their labours induced. As maternal BMI increased, so too did the increase in the number of women requiring IOL – 26.2% of normal-weight women, 30.5% of overweight women, and 34.4% of obese women. Of the women in the study, 3076 had a prolonged pregnancy (defined as ≥41 + 3 weeks of gestation). A significantly higher rate of IOL ending in caesarean section in obese women was observed ( Table 2 ) .

Similar experiences were noted in the UK, where less than half of the obese women (47%) were noted to have laboured spontaneously, one-third (33%) underwent an IOL and one-fifth (20%) underwent a caesarean section prior to labour. The spontaneous labour and induction rate in the general maternity population at the same time were 69% and 20%, respectively .

Obesity is associated with higher rates of failure of induction, with 5.7% of obese women with BMI of 30.0–39.9 kg/m ² and 3.9% of women with a BMI >40.0 kg/m ² requiring caesarean section for a failed IOL in one study of 1273 women induced with prostaglandin . In a population-based cohort study of 80,887 women by Wolfe et al., the rate of failed IOL (as determined by delivery by caesarean section) was 29% in women with BMI >40 kg/m ² , compared with 13% of women with a normal BMI. Factors associated with failure of induction included nulliparity, lack of a previous successful vaginal delivery and presence of macrosomia .

As in the non-obese parturient, IOL may be carried out by various methods, such as prostaglandin, cervical ripening balloon catheter, artificial rupture of the membranes, oxytocin infusion or a combination of these methods. IOL should only be undertaken for the usual obstetric and medical indications. Maternal obesity alone is not an indication for IOL .

The high rate of caesarean section and the morbidity associated with emergency caesarean section in obese women have led to the discussion regarding the consideration of elective caesarean section in morbidly obese women who do not labour spontaneously. Wolfe et al. (2014) demonstrated that the risk of caesarean delivery increased with elective labour induction at term in obese nulliparous women with an unfavourable cervix. This study supports the assertion that labour induction be medically indicated or, if performed for non-medical indications at term, the favourability of the cervix needs to be ensured .

The decision regarding the mode of delivery, however, should take each individual’s circumstances into consideration and include a discussion with the multidisciplinary team responsible for pregnancy care. Obesity class, cervical examination, prior obstetric history and estimated fetal weight also need to be taken into account . The recent Centre for Maternal and Child Enquiries (CMACE) report on maternal obesity in the UK states that “in the absence of obstetric or medical indications, labour and vaginal delivery should be encouraged for women with obesity” .

Location of intrapartum care

With the increased risks of intrapartum complications, along with the added surgical and anaesthetic complications in obese women, it is essential that delivery be conducted in a facility where senior obstetric staff and access to theatre are immediately available. A policy of planning delivery in a regional specialist or tertiary centre, rather than in small, rural maternity units, has been recommended , as access to appropriate care in labour and timely assessment by midwives, obstetricians and anaesthetists should lead to the prevention of delays in performing any necessary interventions and improving outcomes .

The CMACE/Royal College of Obstetricians and Gynaecologists (RCOG) Guidelines on the Management of Women with Obesity (2010) recommend that women with a BMI >35 kg/m ² give birth in a consultant-led obstetric unit as not all facilities have the necessary equipment to enable health professionals to care appropriately and safely for obese women in labour . This is supported by the National Institute for Health and Care Excellence (NICE) Clinical Guideline, which also recommends that women with a BMI between 30.0 and 34.9 kg/m ² undergo an individual risk assessment regarding the planned place of delivery . The CMACE report further recommended that obese women with a BMI >35 may not be suitable for entirely midwifery-based care and that these women give birth in a consultant-led setting . Analysis of the worldwide prevalence of obesity indicate that rural areas and resource-poor settings carry the greatest burden with low-income households and poor education status linked to rising trends in obesity . This creates a dilemma that, whilst recommendations for centralisation of care are based on the concentration of expertise and physical resources to cater to the morbidly obese women, the social and financial upheavals associated with this need to be considered. Although relocation for intrapartum care is a significant burden on the woman, safety in pregnancy is paramount and appropriate support should be put into place to minimise this disruption from home life. If a woman is to relocate for confinement, the timing of this relocation should be guided by local capacity and arrangements. Inter-facility transfer is best conducted prior to the onset of labour, in the antenatal period. Transfer can be problematic once labour has been established due to the increased need for, and the difficulties with, monitoring both the maternal and fetal status, as well as the technical difficulties in arranging appropriate transport for the morbidly obese woman.

Transfer of obese women for intrapartum care

The rise of obesity in rural and regional settings means that, increasingly, medical transport teams are involved in the transfer of obese patients to tertiary-level care. This is an important consideration for countries such as Australia where transfers may involve vast distances. Currently, studies of outcomes of inter-facility transfer of obese parturients are limited. Obese pregnant women provide especially challenging logistical and manual handling issues associated with transfers. Beebe et al. identified various difficulties ambulance crews face when transporting obese patients and illustrate methods used in the US to transport obese patients using modified equipment. In Australia where road transport may be especially prolonged in remote regions, air ambulance services such as the Royal Flying Doctors Service (RFDS) require referring centres to document an accurate weight for their patients. The maximum weight that an aircraft can carry depends on flying time and other necessary equipment. Above approximately 180 kg, the RFDS advises that alternate road transport may need to be organised . With road transport, difficulties can be experienced even with simple care procedures such as the use of bedpans, insertion of indwelling catheters, pressure care and respiratory care . The importance of early assessment and planning for early inter-facility transfer is stressed by many studies and guidelines .