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Pregnancy Care Guidelines

32 Hyperglycaemia

Identifying the risk or presence of hyperglycaemia in pregnancy enables women to receive early testing if risk factors are present and lifestyle advice, education, blood glucose monitoring and appropriate treatment if diabetes is identified.

32.1 Background

Hyperglycaemia (raised blood glucose level) in pregnancy is defined here as pre-existing type 1 diabetes, pre-existing type 2 diabetes (either previously diagnosed or diagnosed during pregnancy) and gestational diabetes (developing during pregnancy). Gestational diabetes can recur in subsequent pregnancies, and women who develop gestational diabetes are at high risk of developing type 2 diabetes in later life.

This section does not address the care of women diagnosed with Type 1 or type 2 diabetes before pregnancy as the Guidelines cover the antenatal care of healthy pregnant women (ie those who do not have identified pre-existing conditions). For women with diagnosed type 1 or type 2 diabetes, preconception counselling is recommended.

32.1.1 Prevalence of hyperglycaemia in pregnancy

The prevalence of hyperglycaemia in pregnancy varies with the characteristics of the population being tested and the diagnostic criteria used. Population-based studies have estimated prevalence ranging from 1% to 50% (Hartling et al 2012). The prevalence of hyperglycaemia in pregnancy has increased over the past decades in parallel with the increase in rates of obesity (BMI > 30 kg/m2) and type 2 diabetes and this trend is expected to continue (Aljohani et al 2008; Hartling et al 2012).

Among women who gave birth in Australia in 2009–11, 0.7% had known pre-existing diabetes (type 1 or type 2 diabetes) and 5.8% developed gestational diabetes (AIHW 2014).

In 2013, rates of known pre-existing diabetes were (AIHW 2016):

  • lowest among women aged <20 years (0.4%) and highest among women aged ≥40 years
  • lower among nulliparous women (1.0%) than among women of higher parity (ie 1.9% for parity of four)
  • higher among Aboriginal and Torres Strait Islander women (4.4%) than among non-Indigenous women (1.1%) (age-standardised)
  • higher among women born overseas (1.2%) than among women born in Australia (0.9%).

32.1.2 Risks associated with diabetes in pregnancy

Cohort studies have found an independent relationship between hyperglycaemia during pregnancy and adverse outcomes for mother and baby (Sacks et al 1995; Sermer et al 1998; Schmidt et al 2001; HAPO Study Cooperative Research Group 2008). The most comprehensive of these studies, the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, showed a continuum of risk across maternal glucose levels for adverse pregnancy outcomes, including pre-eclampsia, caesarean section, birth trauma, high birth weight (>90th centile) and percentage of body fat as well as premature birth (HAPO Study Cooperative Research Group 2008). High birth weight babies are at risk of birth complications (eg shoulder dystocia) (Crowther et al 2005; Falavigna et al 2012), jaundice (Nold & Georgieff 2004) and of long-term effects including childhood overweight (Li et al 1987; Langer et al 1989) and metabolic factors that may increase risk of type 2 diabetes and cardiovascular disease (Garner et al 1997).

In Australia in 2005–07 (AIHW 2010):

  • women with pre-existing type 1 or type 2 diabetes were more likely to have preterm birth, induced labour, caesarean birth, hypertension and hospital stay longer than 7 days than women with gestational diabetes or without type 1 or type 2 diabetes identified in pregnancy and their babies had higher rates of stillbirth, high birth weight, low Apgar score and admission to special care nursery/neonatal intensive care unit
  • women with gestational diabetes had a higher risk of induced labour, preterm birth, caesarean section, hypertension and longer hospital stay than women without gestational diabetes, and their babies were more likely to be admitted to a special care nursery/neonatal intensive care unit
  • Aboriginal and Torres Strait Islander mothers with pre-existing diabetes or gestational diabetes were at the greatest risk of preterm birth, induced labour, caesarean section and hypertension and their babies had higher rates of stillbirth, low Apgar score and admission to neonatal intensive care unit than non-Indigenous babies of mothers with pre-existing diabetes or gestational diabetes.

While hyperglycaemia is the principal concern of diabetes in pregnancy, hypertension and dyslipidaemia associated with diabetes also contribute to the risk of adverse outcomes.

32.2 Assessing risk of diabetes

32.2.1 Identifying women at risk of diabetes during pregnancy

The risk factors for undiagnosed type 2 diabetes are similar to those for gestational diabetes. There is a considerable body of evidence supporting an independent association between increased risk of gestational diabetes and the following factors.

  • Age: Risk increases with maternal age (Scott et al 2002; Gonzalez-Clemente et al 2007; Iqbal et al 2007; Cypryk et al 2008; Karcaaltincaba et al 2009; Yang et al 2009; Ogonowski & Miazgowski 2010; Yogev et al 2010; Ismail et al 2011; Nanda et al 2011; Teede et al 2011; Teh et al 2011; Far et al 2012; Hartling et al 2012; Makgoba et al 2012; Ramos-Levi et al 2012).
  • Weight: Risk increases with increased BMI (Scott et al 2002; Gonzalez-Clemente et al 2007; Rudra et al 2007; Cypryk et al 2008; Kwak et al 2008; Radesky et al 2008; Torloni et al 2009; Yang et al 2009; Ogonowski & Miazgowski 2010; Waugh et al 2010; Nanda et al 2011; Schneider et al 2011; Teede et al 2011; Teh et al 2011; Far et al 2012; Hartling et al 2012; Hedderson et al 2012; Heude et al 2012; Lagerros et al 2012; Makgoba et al 2012; Ramos-Levi et al 2012; Singh et al 2012) or percentage of body fat (Iqbal et al 2007). BMI thresholds for increased risk vary by ethnic group (ie are lower among Asian women) (Hedderson et al 2012). Excessive weight gain early in pregnancy also contributes to risk (Hedderson et al 2010b; Ogonowski & Miazgowski 2010; Ismail et al 2011; Carreno et al 2012; Gibson et al 2012; Heude et al 2012).
  • Polycystic ovary syndrome: The glucose metabolism alterations associated with polycystic ovary syndrome lead to an increased risk of gestational diabetes (Boomsma et al 2006; Toulis et al 2009; Hartling et al 2012; Reyes-Munoz et al 2012).
  • Previous obstetric history: Risk is increased among women with previous gestational diabetes (Gonzalez-Clemente et al 2007; Radesky et al 2008; Getahun et al 2010; Ogonowski & Miazgowski 2010; Waugh et al 2010; Nanda et al 2011; Teede et al 2011; Teh et al 2011; Hartling et al 2012), a previous high birth weight baby (Cypryk et al 2008; Ogonowski & Miazgowski 2010; Waugh et al 2010; Nanda et al 2011; Hartling et al 2012) or previous pregnancy losses, including spontaneous miscarriage and unexplained stillbirth (Hartling et al 2012)
  • Family history: Family history of diabetes, especially maternal family history (Scott et al 2002; McLean et al 2006; Gonzalez-Clemente et al 2007; Cypryk et al 2008; Yang et al 2009; Waugh et al 2010; Ismail et al 2011; Teede et al 2011; Teh et al 2011; Mao et al 2012; Ramos-Levi et al 2012) or type 2 diabetes in a first-degree relative (Ogonowski & Miazgowski 2010; Nanda et al 2011; Hartling et al 2012), increases the risk of developing gestational diabetes.
  • Ethnic origin: Risk of gestational diabetes is increased among women who originate from an ethnic group with a high prevalence of type 2 diabetes (Waugh et al 2010). These include Aboriginal and Torres Strait Islander peoples (Porter et al 2012) and people who are of Hispanic, African, Native American, South or East Asian or Pacific Island origin (Scott et al 2002; Nanda et al 2011; Teede et al 2011; Teh et al 2011; Hartling et al 2012; Makgoba et al 2012; Singh et al 2012).
  • Migration: Being a migrant (including entering another country as a refugee) rather than being native to the country is associated with increased risk (Hedderson et al 2010a; Gagnon et al 2011; Schneider et al 2011).

A recent systematic review (NZ MoH 2014) had similar findings and noted that it is likely that interactions between risk factors, rather than any single risk factor, predispose a woman to gestational diabetes.

Recommendation

  • Evidence-based
  • 34

In the first trimester, assess a woman’s risk of hyperglycaemia including: her age, body mass index, previous gestational diabetes or high birth weight baby, family history of diabetes, presence of polycystic ovarian syndrome and whether she is from an ethnic group with high prevalence of diabetes, such as Aboriginal and Torres Strait Islander peoples

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

32.2.2 Lifestyle interventions for preventing gestational diabetes

  • Physical activity: A Cochrane review (Han et al 2012) concluded that exercise programs had no clear effect on preventing gestational diabetes among healthy pregnant women. An RCT found that a physical activity intervention did not reduce the risk of healthy pregnant women developing gestational diabetes but reduced maternal weight gain, risk of caesarean section and high birth weight (Barakat et al 2013).
  • Dietary interventions: A systematic review of RCTs found that a low glycaemic index diet reduced the risk of a high birth weight baby, that any dietary counselling was effective in reducing the incidence of gestational diabetes compared to standard care and that dietary counselling with probiotics was more effective in reducing incidence of gestational diabetes than dietary counselling alone (Oostdam et al 2011). An RCT found that a low glycaemic index diet during pregnancy did not reduce the risk of having a high birth weight baby among women at risk of gestational diabetes but had a beneficial effect on maternal weight gain and glucose intolerance (Walsh et al 2012).
  • Combined interventions: RCTs into the effect of advice on diet and physical activity in preventing gestational diabetes have inconsistent results. In some studies, intervention did not reduce the risk of gestational diabetes among women at high risk but resulted in lower weight gain among women at high risk and healthy pregnant women (Korpi-Hyovalti et al 2011; Phelan et al 2011; Vinter et al 2011; Hui et al 2012). Other studies found that combined interventions reduced the risk of gestational diabetes and weight gain among women who were overweight or obese (Petrella et al 2013) and the incidence of high birth weight newborns among women at high risk (Luoto et al 2011).
  • Management plans: An Australian study reported that a four-step management plan (including continuity of carer, weighing at each visit, brief food technologist intervention and clinical psychology management) aiming to reduce maternal weight gain among women who were obese reduced the incidence of gestational diabetes and maternal weight gain (Quinlivan et al 2011).

Recommendation

  • Qualified evidence-based
  • 35

Advise women that physical activity and healthy eating during pregnancy help to reduce excessive weight gain but do not appear to directly reduce the risk of diabetes in pregnancy.

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

Chapter 11 includes advice on nutrition and physical activity and Chapter 19 advice on weight management.

32.3 Testing for hyperglycaemia

There is no agreement among current guidelines on whether testing for hyperglycaemia should be offered to all women or only to women with risk factors. However, a number of major international guidelines recommend universal testing for gestational diabetes at 24–28 weeks gestation, including the Australasian Diabetes in Pregnancy Society (ADIPS) (Nankervis et al 2013), the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG 2014), the Endocrine Society (USA) (Blumer et al 2013), the International Association of Diabetes and Pregnancy Study Groups (IADPSG) (Metzger et al 2010), the United States Preventive Services Task Force (USPSTF 2014), the World Health Organization (WHO 2013), the International Federation of Gynecology and Obstetrics (Hod et al 2015) and the International Diabetes Federation (IDF 2015).

The decision to test all pregnant women or only those with risk factors depends on the background frequency of abnormal glucose metabolism in the population and on local circumstances (Metzger et al 2010). The WHO guidelines leave it to local health authorities to specify the testing coverage according to local burden, resources and priorities (WHO 2013). Whether testing is universal or risk factor based, it is important that organisational protocols are consistently followed and outcomes audited.

A technical report from the United Kingdom concluded that testing for hyperglycaemia in pregnancy is worthwhile due to the costs of managing pregnancies complicated by diabetes (Waugh et al 2010). An Australian study suggested that treating mild gestational diabetes involved additional costs to hospitals and women but resulted in reductions in perinatal mortality and serious perinatal complications (Moss et al 2007).

These Guidelines recommend a two-stage approach to testing, with women at risk of hyperglycaemia tested early in pregnancy and women who are not part of this group tested later at 24–28 weeks gestation.

32.3.1 Early testing for hyperglycaemia

Detection and treatment of undiagnosed type 1 or type 2 diabetes in early pregnancy has the potential to reduce immediate and long-term harm to the baby and have a positive effect on maternal health (Hughes & Moore 2013). For these reasons, it has been recommended that women with risk factors for type 2 diabetes be tested for hyperglycaemia at the first antenatal visit (Simmons & Campbell 2007; ADA 2013).

In New Zealand, it is recommended that all women are offered glycated haemoglobin (HbA1c) testing at the first antenatal visit (NZ MoH 2014). Prospective cohort studies in New Zealand since the introduction of the recommendation have found that:

  • HbA1c ≥41 mmol/mol (5.9%) had a sensitivity of 100% (95%CI 91.8 to 100) and specificity of 97.4% (95%CI 95.5 to 99.2) for detecting diabetes and that women with HbA1c of 41–46 mmol/mol (5.9–6.4%) (n=200) had poorer pregnancy outcomes than those with HbA1c <41 mmol/mol (n=7,897; very low quality evidence) (Hughes et al 2014)
  • earlier treatment (<24 weeks) for women with an HbA1c of 41–49 mmol/mol (5.9–6.6%) was associated with a reduced risk of pre-eclampsia (but not other pregnancy or neonatal outcomes) compared with treatment ≥24 weeks (1.5 vs 8.0%, adjusted P=0.03; very low quality evidence) (Rowan et al 2016).

However, the evidence on HbA1c as a test in early pregnancy is limited and it is not currently included in the Medicare Benefits Schedule as a diagnostic test in pregnancy. Further research is needed to evaluate the benefit of early treatment for hyperglycaemia in pregnancy.

Recommendation

  • Consensus-based
  • XXXIX

When a woman has risk factors for hyperglycaemia in the first trimester, suitable tests are glycated haemoglobin (HbA1c) or fasting blood glucose. 

Approved by NHMRC in October 2017; expires October 2022 UNDER REVIEW

Suggested thresholds for identifying hyperglycaemia in early pregnancy are given in Table F2.

Table F2: Suggested thresholds for glycated haemoglobin and fasting plasma glucose to identify hyperglycaemia in early pregnancy

A list of suggested thresholds for glycated haemoglobin and fasting plasma glucose to identify hyperglycaemia in early pregnancy.
Test Suggested threshold
HbA1c ≥41 mmol/mol (5.9%)
Fasting plasma glucose 6.1 to 6.9 mmol/L

Sources: (NZ MoH 2014; McIntyre et al 2016).

32.3.2 Testing for gestational diabetes

A lack of an agreed gold standard for diagnosing hyperglycaemia creates challenges for assessing the accuracy of tests, making comparisons between them and establishing clear thresholds (Hartling et al 2012). There is currently no universally accepted testing or diagnostic regimen. A Cochrane review concluded that, although gestational diabetes was more likely to be detected when all women were tested, the effects of subsequent management on health outcomes are unclear (Tieu et al 2014). A large retrospective cohort study concluded that selective testing would miss one third of women with gestational diabetes (Cosson et al 2013). As the condition is prevalent, asymptomatic and benefits from treatment, universal testing is generally recommended. However, at present, the benefits of treating early hyperglycaemia in pregnancy are uncertain.

International consensus guidelines recommend the use of fasting plasma glucose or plasma glucose 1 hour and 2 hours after 75 g glucose loading for testing for gestational diabetes (Metzger et al 2010; WHO 2013; Hod et al 2015; IDF 2015). HbA1c is not recommended as a test for gestational diabetes due to a lack of sensitivity (NZ MoH 2014).

Recommendation

  • Consensus-based
  • XL

Between 24 and 28 weeks gestation, advise testing for hyperglycaemia to all women who have not previously been tested in the current pregnancy. Advise repeat testing to women who were tested early in pregnancy due to risk factors and who had a normal result on an initial test.

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

32.3.3 Diagnostic thresholds

The optimal diagnostic threshold for diabetes in pregnancy is uncertain and difficult to determine based on the available evidence.

After review of the findings of the HAPO Study, the IADPSG defined diagnostic values on the basis of an odds ratio of 1.75 for adverse neonatal outcomes. These criteria use a one-step approach to testing for gestational diabetes and have been adopted by the WHO (WHO 2013) and the American Diabetes Association (ADA 2013). Recent ADIPS guidelines on diagnosis of gestational diabetes also include these criteria (Nankervis et al 2013). Other documents, including the RACGP/Diabetes Australia Diabetes Management in General Practice (RACGP/Diabetes Australia 2013) and a US National Institutes of Health consensus development conference statement (VanDorsten et al 2013) support the use of a two-step approach to testing and higher thresholds.

Table F3: WHO/IADPSG criteria for diagnosis of diabetes in pregnancy

A list of diabetes doses under the WHO/IADPSG criteria.
WHO/IADPSG criteria mmol/ml/dl dose (diabetes)
Fasting plasma glucose ≥ 7.0 mmol/l (126 mg/ dl)
2-hour plasma glucose ≥ 11.1 mmol/l (200 mg/dl) following a 75g oral glucose load
Random plasma glucose ≥ 11.1 mmol/l (200 mg/ dl) in the presence of diabetes symptoms
WHO/IADPSG criteria mmol/ml/dl dose (gestational diabetes)
Fasting plasma glucose 5.1–6.9 mmol/l (92 -125 mg/dl)
1-hour plasma glucose ≥ 10.0 mmol/l (180 mg/dl) following a 75g oral glucose load
2-hour plasma glucose 8.5–11.0 mmol/l (153 -199 mg/dl) following a 75g oral glucose load

Source: (WHO 2013).

Recommendation

  • Consensus-based
  • XLI

Use the World Health Organization/International Association of Diabetes and Pregnancy Study Groups tests and criteria to diagnose diabetes and gestational diabetes in pregnancy.

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

The WHO criteria for diagnosing pre-existing diabetes are based on the risk of developing microvascular complications, predominantly retinopathy. There are no data available to assess diagnostic accuracy of current diabetes diagnostic criteria if used in pregnancy in untreated women (WHO 2013). The WHO grade the quality of the evidence supporting the criteria for diagnosing gestational diabetes as very low (WHO 2013). The criteria are not based on diagnostic accuracy because there is no reference test to define disease status.

A systematic review found evidence to support a positive association between increasing plasma glucose on a 75 g or 100 g oral glucose tolerance test and high birth weight and primary caesarean section but clear thresholds for increased risk were not identified (Hartling et al 2012). Another systematic review found that the risk of these adverse events was similar between the WHO/IADPSG and former WHO criteria (Wendland et al 2012). Cohort studies have found that women classified as having gestational diabetes under the WHO/ IADPSG criteria but not under former criteria had a significantly increased risk of caesarean section (Lapolla et al 2011; O’Sullivan et al 2011), hypertensive complications (O’Sullivan et al 2011) and having a high birth weight baby (Morikawa et al 2010; O’Sullivan et al 2011). However, no RCTs have compared the outcomes of management following diagnosis under the two criteria.

While a full cost-effectiveness analysis has not been published, two studies that modelled the cost effectiveness of the WHO/IADPSG criteria concluded that they would only be cost effective if detection of gestational diabetes reduced the rate at which type 2 diabetes subsequently developed (Werner et al 2012) or if the rate of caesarean section was reduced (Mission et al 2012).

It is acknowledged that using the WHO/ IADPSG criteria has the potential to increase the diagnosis of gestational diabetes in Australia, with resource implications. However, calculations of the prevalence in populations may increase or decrease with changes to both testing criteria and uptake, as well as changes in population demographics. For example:

  • a prospective study in Wollongong comparing the use of the previous ADIPS criteria with the WHO/ IADPSG criteria found that prevalence varied between the public and private sectors: 8.6% vs 9.1% (public sector), 10.5% vs 16.2% (private sector) and 9.6% vs 13.0% (overall) (Moses et al 2011)
  • an analysis of the HAPO sites in Australia using the WHO/ IADPSG criteria found a prevalence of gestational diabetes of 13.2% in Brisbane and 13.6% in Newcastle (Sacks et al 2012)
  • an analysis of oral glucose tolerance test results from women in two Area Health Services in the Sydney area found that using the WHO/IADPSG criteria rather than the previous ADIPS criteria would increase rates of diagnosis and therefore affect the health service workload for management of gestational diabetes (Flack et al 2010)
  • in a cohort of Aboriginal and Torres Strait Islander women in Far North Queensland, gestational diabetes prevalence increased threefold over 2 years due to enhanced testing practices, but prevalence would have been lower if the WHO/ IADPSG criteria had been in place at the time (Davis et al 2013).

Increased diagnosis also has implications for women. Gestational diabetes occurs across a continuum with a variety of potential threshold points. The risk of labelling a woman with gestational diabetes needs to be weighed against any potential benefits to the woman and baby, particularly if lifestyle advice is likely to be the first treatment option. There is a need for evidence on the risks and benefits of testing at different thresholds.

32.4 Discussing diabetes in pregnancy (gestational diabetes, type 1 or type 2 diabetes)

Discussion to inform a woman’s decision-making about testing for diabetes should take place before testing and include that:

  • undetected and uncontrolled diabetes during pregnancy is associated with risks to the mother (eg high blood pressure, pre-eclampsia) and to the baby in the short term (eg stillbirth, preterm birth, high birth weight, congenital anomalies, birth complications) and the longer term (childhood overweight and development of diabetes)
  • a diagnosis of diabetes in pregnancy may lead to increased monitoring and interventions during pregnancy and labour (eg induced labour, caesarean section).

If diabetes is diagnosed during pregnancy, points for discussion include:

  • the role of diet, physical activity and body weight in managing diabetes
  • the role of insulin or oral hypoglycaemic agents in the management of diabetes (ie if diet and physical activity do not adequately control blood glucose levels)
  • the importance of monitoring and controlling blood glucose levels during pregnancy, labour, birth and early feeding of the baby to reduce the likelihood of the baby having low blood glucose levels after the birth and the associated risks
  • the possibility of the baby having low blood glucose levels in the period after the birth, which may require admission to a special care nursery/neonatal intensive care unit
  • the risk of the baby developing obesity, heart disease and/or diabetes in the future
  • the woman’s increased risk of developing type 2 diabetes and the importance of regular assessment for glucose tolerance and maintaining a healthy weight
  • the benefits of registering with the National Gestational Diabetes Register (eg annual reminders for glucose tolerance assessment)
  • the benefits of breastfeeding in reducing the risk of the woman developing type 2 diabetes in the future
  • whether the woman understands the information she has been given.

32.5 Practice summary: diabetes in pregnancy

When

Assess risk of undiagnosed diabetes or prediabetes at the first antenatal visit and offer testing to women with risk factors.

At 24–28 weeks offer testing to women not already tested and repeat testing to women with risk factors with a previous normal blood glucose level.

Who

  • Midwife
  • GP
  • obstetrician
  • Aboriginal and Torres Strait Islander Health Practitioner
  • Aboriginal and Torres Strait Islander Health Worker
  • multicultural health worker; accredited practising dietitian
  • diabetes educator
  • endocrinologist
  • accredited exercise physiologist.

What

  • Discuss the reasons for testing blood glucose levels
    Explain that diabetes in pregnancy can have effects on the pregnancy and the baby and that early identification and taking steps to manage raised blood glucose as soon as possible can reduce the risk of these effects.
  • Take a holistic approach
    Provide women with practical advice on healthy eating and physical activity (see Chapter 11), taking into consideration the availability of foods and ways of being physically active that are appropriate to the woman’s cultural practices and preferences. Consider a health promotion program to improve community understanding of the effects of diabetes in pregnancy and the importance of healthy lifestyle patterns.
  • Consider referral
    Where possible, women diagnosed with pre-existing diabetes should be referred for specialist assessment (by an endocrinologist or obstetric physician) and education on nutrition, monitoring and management (eg to a multidisciplinary team involving an accredited practising dietitian, diabetes educator, endocrinologist, obstetric physician). Where specialist allied health professionals are not available, other sources of information (eg written information, video or audio resources, telehealth services) may be useful.
  • Document and follow-up
    When a woman’s blood glucose is tested, tell her the results and note them in her antenatal record. Have a system in place so that women diagnosed with diabetes receive ongoing follow-up, including further testing of blood glucose levels after pregnancy. Postnatal education and support are important in preventing or delaying the onset of diabetes in the future and women should be encouraged to attend postnatal testing.

32.6 Resources

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Last updated: 
4 December 2018