General practice management of type 2 diabetes

Gestational diabetes mellitus
☰ Table of contents

Clinical context

Gestational diabetes, or GDM, is defined as glucose intolerance that begins or is first diagnosed during pregnancy. It may appear earlier, particularly in women with a high level of risk for GDM.

GDM generally develops and is diagnosed in the late second or early third trimester of the pregnancy. GDM affects about 9.6–13.6% of pregnancies in Australia.245,246

The reported prevalence of GDM varies for a number of reasons. One reason is the use of different screening and diagnostic criteria. The prevalence is also affected by maternal factors such as history of previous gestational diabetes, ethnicity, advanced maternal age, family history of diabetes, pre-pregnancy weight and high gestational weight gain. Mothers of different ethnicity born in areas with high diabetes prevalence such as Polynesia, Asia and the Middle East, are three times as likely to have GDM as mothers born in Australia. Among Aboriginal and Torres Strait Islander mothers, GDM is twice as common, and pre-gestational diabetes affecting pregnancy is three to four times as common as in non-Indigenous mothers.245

In pregnancy, there is a natural increase in levels of hormones including cortisol, growth hormone, human placental lactogen, and progesterone and prolactin levels, causing two to three fold increases in insulin resistance. The action of these hormones is usually compensated by increased insulin release. In pregnant women with abnormal glucose tolerance or impaired β-cell reserve, the pancreas is unable to sufficiently increase insulin secretion in order to control BGLs.

Potential maternal complications during pregnancy and delivery include pre-eclampsia and higher rates of caesarean delivery, maternal birth injury, postpartum haemorrhage.

For the neonate, complications can include macrosomia (large for gestational age) growth restriction, birth injuries, respiratory distress, hypoglycaemia and jaundice.

The precise level of glucose intolerance characterising GDM has been controversial due to differences in screening, diagnostic criteria and outcomes to which criteria are applied. The NHMRC criteria25 were determined from glucose levels on antenatal glucose tolerance tests that were associated with subsequent development of diabetes in the mother. A recent Cochrane review247 determined that increased levels of screening and management have not been clearly linked to improved health outcomes.

The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study was published in 2008. This study reported a correlation between increasing maternal glucose levels at 24–32 weeks’ gestation and a range of adverse maternal and fetal outcomes. The study suggested that the relationship between increasing BGLs and adverse effects was continuous, with no threshold or inflection point at which lower BGLs confer protection.

In response to the HAPO study, the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) developed new consensus guidelines for the testing and diagnosis of GDM. Although The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) and the Australasian Diabetes in Pregnancy Society (ADIPS)248 have recommended that these consensus guidelines should be implemented, there has been controversy nationally and internationally.249 Independent analysis of the HAPO data by the National Institute for Health and Care Excellence (NICE) guideline groups has suggested alternative diagnostic and management criteria that are not as low as IADPSG criteria,240 and the UK has now developed its own diagnostic criteria.240

Ultimately, there is at present little evidence that clinical intervention is beneficial for the additional women identified by the new screening criteria.250–253 As with any screening intervention, the evidence must be clear that the benefits outweigh potential harms.

Until this evidence is forthcoming, the original NHMRC recommendations for screening of GDM remain the preferred diagnostic criteria preferred by the RACGP.

There is still a need for further studies to clearly outline the evidence of the benefits and risks of altering diagnostic criteria, including the health economic costs of any such consensus for change.

Acknowledging that in Australian general practice there are alternative diagnostic criteria for GDM, the RACGP (preferred) and ADIPS (alternative) diagnostic criteria are presented in Box 9 and in Chapter 16. Issues under debate. Furthermore, it is important that each GP be aware of their obstetric service diagnostic criteria, and support and manage patients in a manner confluent with their specialist team guidelines to avoid conflict and patient confusion.

In practice

Screening for gestational diabetes mellitus

GDM is diagnosed by screening during pregnancy:

  • All pregnant women should be screened between 26 and 28 weeks’ gestation with a non-fasting glucose challenge.
  • Women at high risk (refer to Box 3) should be screened at the first opportunity early in pregnancy and repeat if negative screening at 24–28 weeks.
  • Women whose levels are ≥7.8 mmol/L should have a formal (fasting) 75 g OGTT.
  • The diagnosis of GDM is made on the basis of a 75 g OGTT (Box 9).

Box 9. Screening and diagnosis of gestational diabetes mellitus

Australian Diabetes in Pregnancy Society (ADIPS; alternative criteria)

Fasting plasma glucose 5.1–6.9 mmol/L,
one-hour post ≥10.0 mmol/L, or two-hour 8.5–11.0 mmol/L

The Royal Australian College of General Practitioners (RACGP;preferred criteria)

Fasting plasma glucose ≥5.5 mmol/L,
two-hour plasma glucose or random glucose ≥8.0 mmol/L

ADIPS suggests a universal single step 75 g OGTT at 24–28 weeks.

GPs should be aware of the differences in the diagnostic and management algorithms of the RACGP (preferred) versus ADIPS (alternative) that are relevant to their local referral pathways for patients with gestational diabetes services and pragmatically manage patients within the context of these services.





Pregnant women with gestational diabetes mellitus should be offered dietary advice and blood glucose monitoring, and be treated with glucose-lowering therapy depending on target values for fasting and postprandial targets

SIGN, 2014


*Refer to Summary, explanation and source of recommendations for an explanation of the level of evidence and grade of evidence

The basis for management for women with GDM includes nutritional therapy, weight optimisation, physical activity, blood glucose monitoring and insulin therapy.

All women with GDM should be offered education, blood glucose monitoring and dietary advice. Most GDM responds positively to lifestyle management.254 Referrals to an APD and AEP are advised unless already provided by the obstetric services.

Limiting weight gain in pregnancy for obese or overweight women with GDM is desirable. It is recognised that glycaemic targets in the treatment of GDM vary between centres and clinicians around Australia. Targets suggested by ADIPS criteria have been described within Australia as being aggressive. Care should be taken in approaching these targets as most blood glucose monitors have a 5–10% margin of error and risks of maternal hypoglycaemia need to be considered.

Given the lack of agreement for treatment targets and the accuracy of blood glucose monitors, the RACGP suggests that readings between 4–6 mmol/L preprandially are reasonable.

Metformin has been used internationally65 as initial glucose-lowering treatment in women with GDM. However, it has not been approved for this use in Australia for this indication. Lifestyle and insulin therapy remain the mainstay of therapy.

Close cooperation with the obstetric team is advised to monitor maternal and fetal welfare.

Hypoglycaemia may have serious effects on placental function and the fetus in patients with GDM. Thorough investigation is required in such patients.

Aim to achieve blood glucose levels:

  • between 4 and 6 mmol/L preprandially
  • <7 mmol/L two hours postprandially.

Follow-up of patients with a history of gestational diabetes mellitus




Women with a history of gestational diabetes mellitus should receive a postpartum oral glucose tolerance test at 6–12 weeks

19 American Diabetes Association, 2015


*Refer to Summary, explanation and source of recommendations for an explanation of the level of evidence and grade of evidence

Box 10 provides the RACGP (preferred criteria) and ADIPS (alternative criteria) for follow up of patients with GDM history.

Box 10. Follow up of patients with gestational diabetes mellitus history

The Royal Australian College of General Practitioners (RACGP; preferred criteria)

75 g two-hour oral glucose tolerance test at 6–12 weeks postpartum

Thereafter, a fasting blood glucose or glycated haemoglobin (HbA1c) test every three years


Australian Diabetes in Pregnancy Society (ADIPS; alternative criteria)

 75 g two-hour oral glucose tolerance test, at 6–12 weeks postpartum

The frequency and nature of this surveillance will depend on future pregnancy plans and the perceived risk of converting to type 2 diabetes. Women contemplating another pregnancy should have an oral glucose tolerance test annually


Although GDM usually resolves following birth, it is associated with increased risk for developing maternal type 2 diabetes in later life. The lifetime risk of developing type 2 diabetes following a diagnosis of GDM is 60%.255

After delivery, it is recommended that advice be given on healthy diet and exercise, which may include referral to a dietitian and physical activity program. Encourage increasing physical activity (eg 30 minutes brisk walking five times a week) and/or weight loss, which reduces risk of developing diabetes by 40–60% in those at high risk.256 Breastfeeding is encouraged for its many health advantages.

Women with normal glucose tolerance should be counselled regarding their risk of developing GDM in subsequent pregnancies.

Diabetes Australian and RACGP logo's
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