Management of obesity in pregnancy

Abstract

The prevalence of obesity in women of reproductive age continues to increase globally. Almost 50% of women entering pregnancy in Australia now have overweight (body mass index (BMI) 25 to <30 kg/m2) or obesity (BMI ≥30 kg/m2).1 Obesity in pregnancy disproportionately impacts vulnerable maternal populations, including Aboriginal and Torres Strait Islander women.2 Maternal obesity increases the risk of obstetric complications including subfertility, early pregnancy loss and poor pregnancy outcomes (Table S1).3, 4 Furthermore, the transgenerational impact of obesity in pregnancy is a key driver of the global epidemic of obesity, diabetes, and cardiovascular disease for women and their offspring.3 Pre-pregnancy counselling underpins the management of obesity in pregnancy and includes calculation of BMI, weight optimisation, discussion on appropriate contraception, and screening for obesity-related comorbidities including concomitant eating disorders.5, 6 Addressing obesity in the preconception period allows informative discussion on risk associated with conception and pregnancy and the opportunity for weight loss to modify complications. Pre-pregnancy screening for comorbidities such as pre-existing diabetes mellitus and hypertension is also recommended.5 Optimising glycaemic control, assessment of associated microvascular and macrovascular complications such as retinopathy and renal disease and management of blood pressure with non-teratogenic anti-hypertensive medications are required to optimise pregnancy outcomes.7 While it is well established that improving maternal BMI and lifestyle prior to pregnancy improves fertility and pregnancy complications associated with maternal obesity, there are few randomised controlled trials (RCTs) evaluating specific interventions.8 Two recent RCTs evaluated the effectiveness of pre-pregnancy weight loss interventions in women with obesity.9, 10 The Pregnancy Outcomes after Preconception weight loss (POP) study (n = 164) demonstrated no impact on the primary outcome of fasting glucose at 26–28 weeks gestation, but a significant reduction in the (exploratory) composite obesity-related adverse maternal and perinatal outcomes following a 12 weeks modified very low energy diet (VLED) (800 calories per day) compared to a standard dietary intervention. Substantially greater weight loss was achieved in the VLED group (13.0 kg vs 3.2 kg; P < 0.01).9 The US Prepare trial (n = 326) showed that a behavioural weight loss intervention comprising regular telephone coaching sessions until completion of pregnancy was associated with greater pre-pregnancy weight loss compared with usual care (3.7 kg vs 0.6 kg; P < 0.001), but greater gestational weight gain (GWG) (13.2 kg vs 10.3 kg; P = 0.03). Secondary/exploratory analysis demonstrated no difference in pregnancy outcomes, except for spontaneous pregnancy loss (5% vs 12%) and lower rates of gestational diabetes (GDM) in early pregnancy (25% vs 35%).10 The PreBABE (ACTRN12620001238965) and Begin Better (ACTRN12621000128897) RCTs are currently recruiting in Australia, evaluating the impact of a 10-week partial VLED and multi-disciplinary counselling via an online app, respectively, on pregnancy outcomes. In the pre-pregnancy setting, adjunctive weight loss pharmacotherapies such as phentermine and liraglutide are effective, but are contraindicated in pregnancy due to their potential teratogenicity. It is imperative that women are counselled on effective contraception while on obesity pharmacotherapy, with an appropriate washout interval following therapy cessation. Bariatric surgery remains the most effective long-term treatment for obesity.3 In Australia, most bariatric surgery occurs in women of reproductive age, with the most common procedure now the vertical sleeve gastrectomy.11 Bariatric surgery can improve fertility through restoration of ovulation and can reduce the risk of pregnancy complications associated with maternal obesity, but is associated with increased risk of small-for-gestational-age (SGA) infants. This may relate to the increased risk of micro- and macronutrient deficiencies due to malabsorption, hypoglycaemia and greater glycaemic variability. Women should be advised to delay pregnancy until they have achieved weight maintenance (generally 1–2 years post-surgery) and all micronutrient deficiencies have been addressed.12 During pregnancy, the US Institute of Medicine (IOM) recommends an overall GWG of 5–9 kg for women with overweight pre-pregnancy and 7–11.5 kg for women with obesity, correlating with the lowest risk for complications including SGA and large for gestational age (LGA) infants, caesarean section, preterm birth, and postpartum weight retention.13 Evidence shows that GWG in excess of the IOM recommendations is associated with worse pregnancy outcomes.3 However, there is evidence to support lower GWG targets, stratified by Obesity Class (I–III). Nevertheless, the IOM recommendations are exceeded in around half of pregnancies, particularly in women with overweight and obesity.14 A recent systematic review and meta-analysis of 117 RCTs of interventions during pregnancy (34 546 pregnancies) found that structured antenatal diet and physical activity interventions reduced the incidence of preterm births, LGA infants, GDM, and neonatal intensive care unit admissions, despite being associated with only minimal GWG reduction (2.6 kg (95% CI 1.4–3.9 kg) and 1.0 kg (95% CI 0.74–1.3 kg), respectively).15 LIMIT, the largest RCT of antenatal diet and lifestyle in 2212 women with overweight or obesity in pregnancy, which showed no effect on GWG or pregnancy outcomes despite improvement in diet and physical activity behaviour, was not included in this analysis.16 Similarly, the 2021 US Preventive Services Task Force review of 68 behavioural intervention studies to limit GWG reported a modest reduction in GWG and decreased risk of GDM, emergency caesarean delivery, macrosomia, and LGA infants, with increased benefit observed for higher-intensity interventions. Notably, a significant association between SGA infants and intervention intensity was also found.17 In contrast, the International Weight Management in Pregnancy (i-WIP) Collaborative Group meta-analyses of individual participant data (IPD) from RCTs in women with overweight or obesity showed limited evidence for clinically relevant improvement in pregnancy outcomes or GWG (mean GWG difference −0.70 kg (95% CI −0.92 to −0.48 kg)). While a reduced risk of caesarean section was observed, as well as a reduced risk of GDM when IPD was supplemented with data from studies that did not provide IPD, there was no effect on other pregnancy outcomes or on the risk of early childhood obesity.18 A multi-disciplinary team is central to optimising the management of women with obesity in pregnancy, including midwifery, obstetric, anaesthetic and endocrinology/obstetric medicine physician involvement. The availability of bariatric equipment, appropriate additional resources including for intrapartum or operative delivery such as aids for patient transfers, ultrasound for vascular access and spinal placement also warrants consideration.5, 7 Centres should develop local policies to ensure the safety of women with obesity in pregnancy, including limitations of care in smaller centres. Screening and management of obesity-related comorbidities and complications such as hyperglycaemia in pregnancy, pre-eclampsia, obstructive sleep apnoea, fetal anomalies, excessive or inadequate fetal growth and fetal abnormalities is required as part of a systematic clinical approach.3, 14 Women with risk factors for pre-eclampsia or who are high-risk based on a screening algorithm may be considered for prophylactic low-dose aspirin to modify their risk for early-onset pre-eclampsia, ideally before 16 weeks gestation.14 Regular monitoring and discussion of GWG targets with practical interventions including diet and behavioural advice and access to metabolic specialist services where possible is also recommended.3, 5 Ideally, this would include specialist care early in the first trimester, appropriate location of care and increased maternal and fetal monitoring and review.5, 7 There is debate regarding increased frequency of fetal growth and wellbeing ultrasound monitoring. Women with obesity have a twofold increased risk of having LGA infants; however, prevalence of SGA is controversial, although there is likely higher risk in patients with comorbidities such as pre-eclampsia.14 There are limitations of ultrasound accuracy for both estimated fetal weight and detection of fetal anomalies due to increased maternal central adiposity.5 However, the LIMIT collaborative group showed that fetal ultrasound can accurately predict neonatal anthropometry.19 Royal Australian and New Zealand College of Obstetricians and Gynaecologists guidelines recommend third-trimester ultrasound and consideration for serial ultrasounds to monitor fetal growth and wellbeing,5 ideally in a tertiary centre (Fig. S1). The optimal timing of delivery for women with obesity in pregnancy is unknown; however, delivery prior to 40 weeks may reduce the risk of stillbirth, postpartum haemorrhage and birth trauma including shoulder dystocia.3 Earlier delivery may also be indicated for medical and fetal comorbidities. Rates of induction of labour are higher in women with overweight and obesity, as is the duration of the first stage of labour and for the induction to be unsuccessful.14 Notably, induction of labour prior to 40 weeks gestation reduces the rates of emergency caesarean section in women with obesity.7 Emergency caesarean section is associated with a higher risk of maternal morbidity due to anaesthetic, mechanical and operative difficulties with reported rates as high as 40%.5 Rates of intervention among women with Class III obesity (BMI ≥40 kg/m2) are particularly high. In a report from a specialised antenatal clinic in a tertiary referral centre, published in this issue of ANZJOG, 49% of women had an induced labour, 45% had a pre-labour caesarean delivery, only 5% experienced a spontaneous onset of labour, and the overall rate of caesarean delivery was 61%.20 Maternal obesity is also a risk factor for unsuccessful vaginal birth after caesarean section (VBAC) with a reported vaginal delivery rate of 55% compared with 71% among women with a normal BMI. The risk of uterine rupture with VBAC is also increased for women with Class III obesity.21 Discussion of these risks, including the risks associated with emergency caesarean section, should be raised with women when planning for delivery (Fig. S1). In summary, obesity in pregnancy is associated with a range of pregnancy complications and long-term health consequences for both mother and offspring. Sensitive counselling about the risks of overweight and obesity and the available management options are required. The evidence to support preconception and pregnancy intervention and management approaches to obesity in pregnancy continues to evolve. Nevertheless, caring for these women requires multi-disciplinary expertise as well as preconception (and postpartum) planning to mitigate risk and optimise maternal weight prior to pregnancy. Figure S1: Management of obesity in pregnancy.3, 5, 14 Table S1: Complications of obesity in pregnancy. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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