Table of contents
Current issue
Search journal
Archived issues
NZMJ Obituaries
Hotline (free ads)
How to subscribe
How to contribute
How to advertise
Contact Us
Other journals
The New Zealand Medical Journal

 Journal of the New Zealand Medical Association, 14-March-2008, Vol 121 No 1270

Screening, diagnosis and services for women with gestational diabetes mellitus (GDM) in New Zealand: a technical report from the National GDM Technical Working Party
David Simmons, Janet Rowan, Rosemary Reid, Norma Campbell; on behalf of the National GDM Working Party*
Rates of gestational diabetes mellitus (GDM) and Type 2 diabetes in pregnancy are increasing with the epidemic of obesity. GDM is associated with significant perinatal morbidity and future risk of permanent diabetes in the mother and obesity and diabetes in the offspring. The recent Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS) has shown maternal and perinatal benefits of managing GDM once diagnosed. The criteria for GDM are under review following the recent completion of the Hyperglycaemia and Adverse Perinatal Outcomes study (HAPO).
In New Zealand, the approach to identifying women with GDM or undiagnosed Type 2 diabetes has varied. The National GDM Technical Working Party reviewed the available data in the New Zealand context and recommend that (1) All pregnant women are offered screening for GDM backed up with relevant educational, systems and materials for health professionals and the women; (2) Criteria for GDM should remain unchanged pending further information (which should be actively sought); (3) Women at high risk of undiagnosed Type 2 diabetes in pregnancy should be screened at booking: the HbA1c was recommended as a practical initial screening test, but further research is needed; and (4) A structured, audited, population-based approach to managing women with GDM should be introduced in each district.


Gestational diabetes (GDM) is associated with maternal (pre-eclampsia, caesarean section, and perineal trauma) and perinatal (macrosomia, stillbirth, shoulder dystocia, birth injuries, hypoglycaemia, respiratory distress, stillbirth, and jaundice) complications.1 GDM is also associated with an increased risk of later Type 2 diabetes in both the mother and the offspring.2,3 Pregnancy is the only time to identify women with GDM, and provides the opportunity to implement strategies to improve both pregnancy and long-term outcomes.
The diagnosis of GDM in New Zealand (NZ) is generally made using a two-step approach. An initial screening test involves a non-fasting 50 glucose challenge test (GCT) at 24–28 weeks’ gestation.1 Women are subsequently referred for a diagnostic 75g oral glucose tolerance test (OGTT) if the 1-hour glucose concentration is ≥7.8 mmol/L.
Currently, GDM is diagnosed if the fasting glucose is ≥5.5 mmol/L and/or the 2-hour glucose concentration is ≥9.0 mmol/L. These diagnostic criteria have been used since 1992 and are unique to NZ.1,4 Many other countries use lower glucose levels to diagnose GDM.5
The current criteria for diagnosing GDM are used throughout NZ,6 but the extent of screening for GDM varies markedly. Figure 1 shows the uptake of the 50g GCT by District Health Boards (DHBs) in 2005, ranging from approximately 20% to 89% of pregnancies. This is not surprising as, until the end of 2006, some organisations promoted screening for all pregnant women,4,7 while others recommended screening women with one or more of seven clinical risk factors.8 Similar discordance is also seen between different global screening recommendations.6
There are several reasons for reviewing the current approach to screening for GDM. Firstly, since the most potent nihilistic view of GDM was published in 1993,9 a great deal has changed from both global and knowledge perspectives. The world now faces a pandemic of diabetes and obesity,10,11 which has resulted in growing numbers of young women with risk factors for GDM or undiagnosed Type 2 diabetes.12–14 Type 2 diabetes in pregnancy is associated with high rates of fetal loss, congenital malformations, and other adverse perinatal outcomes.14
Figure 1. Proportion of births where the mother had a glucose challenge test for each District Health Board (DHB). Proportions are shown for women aged below and above 25 years.
Polycose (Glucose Challenge) Testing as a % of Live Births by DHB
Secondly, there is good evidence that the development of Type 2 diabetes in high risk populations can be prevented or delayed,15–17 thus providing women with GDM the chance to actively try to delay/reduce their chance of permanent diabetes. Interventions are potentially useful for their children, as the intrauterine and postnatal environment influence later health risks (including obesity) for the child.18–20
Thirdly, two recent studies have made important contributions with respect to the value of treating women with GDM during pregnancy. These are the prospective, randomised Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS)21 and a case control study by Langer.22 Both studies showed significant benefit from the treatment of GDM and support other studies showing the benefits of tight glucose control during GDM.23,24 In addition, ACHOIS laid to rest concerns that a diagnosis of GDM could be associated with increased caesarean section rates or maternal psychological trauma. The caesarean section rates were not increased in women treated for GDM and maternal well-being scores were better in women treated for GDM.
With the combination of all these reasons it was timely to review the approach to screening, diagnosis and models of care for women with GDM in NZ. The Australasian Diabetes in Pregnancy Society (ADIPS) and the New Zealand College of Midwives (NZCOM) worked with representatives from other relevant organisations (Appendix 1) to develop a Technical Report to contribute to this debate. This paper describes the process undertaken and summarises the recommendations made.

The National GDM Technical Working Party process

An open national workshop hosted by ADIPS and NZCOM was held on 10 March 2006 to discuss screening for, and management of, GDM. Presentations included reviews of the current epidemic of obesity and diabetes in NZ.
Presentations focussed on:
  • Recent evidence confirming benefits of treating women with GDM;
  • The inter-generational effect of exposure of the fetus to maternal diabetes;
  • Interventions that reduce progression to Type 2 diabetes in high-risk populations;
  • Potential long-term health benefits for women and their children by identifying and treating GDM; and
  • The rationale for promoting a general, rather than selective, screening approach for GDM, and the controversies around the criteria for diagnosis of GDM and how these may be solved.
A smaller Technical Working Party was established with representatives from stakeholder organisations to develop a Technical Report. The first meeting was on 1 June 2006 to consider GDM within the unique circumstances of the NZ demography and health services. Four groups were formed to address the main issues that had been identified with respect to screening and diagnosis of GDM (described below). Each group provided a written summary of the evidence and made a number of recommendations. These contributed to the body of the Technical Report, which is available for use to ensure that appropriate care is available for women during pregnancy.
The draft report was circulated to the member organisations, which led to minor amendments being made. The final report is available on
The four main issues are outlined below.

(1) Should all pregnant women without known diabetes be offered screening for GDM? If so, how?

There is consensus that screening for GDM should be offered in NZ,6 but a debate exists about whether to offer screening to all women or only those with risk factors. GDM fulfils the criteria for a condition warranting screening in NZ,25 as part of routine clinical care, not as a national screening programme (as occurs with cancers of the cervix and breast).
The benefits from screening for GDM are to:
  • Reduce adverse pregnancy outcomes in women subsequently diagnosed and treated for GDM;
  • Reduce risks in subsequent pregnancies by increasing the likelihood of preconceptual identification and management of undiagnosed diabetes; and to
  • Provide education to women with GDM about their predisposition to Type 2 diabetes in association with advice about how to reduce this risk for themselves and (potentially) their children.
Risk factor-based approaches miss a sizable proportion of women with GDM.26 In NZ, even women with risk factors are not being screened27—possibly due to the complexity of this approach. A routine offer of screening would reduce these issues. When offering any screening test it is important that accurate information is provided so that women can decide whether to be screened or not. This includes information about the performance of the test itself, consistent with the Code of Health and Disability Services Consumers' Rights.28
All women should receive an offer of routine screening for GDM
For this to occur, it is crucial that:
  • Relevant health professionals understand the rationale behind the screening and diagnostic process, and are provided with resources to maintain currency so they are able to advise women and implement screening in a woman-focussed manner;
  • There is written information available about the implications of screening and diagnosis of GDM that is nationally consistent and easily understood by women;
  • Women are informed about their management options should they be diagnosed with GDM and remain the central focus of the model of care provided;
  • Women are informed about screening in a timely and appropriate way;
  • There is documentation that screening for GDM has been discussed, relevant information provided to the woman and the woman has consented to screening; and
  • There is a system to ensure that screening for and management of GDM are continuously assessed, to allow development of further improvements.

(2) What should the diagnostic criteria be for GDM in New Zealand?

Currently, there is no global consensus on criteria for diagnosing GDM.6 Glucose concentrations are a continuum with intra-individual variability, so there is no clear separation between a normal and an abnormal glucose level.
When deciding diagnostic criteria, a balance is needed so that women who would benefit from treatment are not missed but other women are not needlessly labelled/treated. While ACHOIS21 used a 2-hour cutoff of 7.8 mmol/L to diagnose GDM (also now recommended by the International Diabetes Federation29), the study was not large enough to show a “cut point” for benefit. However, in NZ, dropping from 9.0 mmol/L to 7.8 mmol/L (or 8.0 mmol/L as endorsed by the Australian branch of ADIPS) would increase the number of women diagnosed with GDM by an estimated 52%: numbers unable to be managed by existing diabetes in pregnancy services. Any change would need to consider resources and cost-effectiveness.
Moreover, a large study of 25,000 women across 15 countries (the Hyperglycemia and Adverse Pregnancy Outcomes study—HAPO) will report on the relationship between pregnancy outcomes and maternal glycaemia in 2007.30 The study is powered to relate the fasting, 1-hour, and 2-hour glucose levels to outcomes by 0.5 mmol/L increments, providing relevant data regarding diagnostic criteria for GDM.
  • Whilst there is evidence that a lower 2-hour glucose level during the 75 g OGTT is associated with a reduction in adverse pregnancy outcomes, there are no clear data demonstrating an optimal level. The Technical Working Party recommend that the status quo be retained and data reviewed again when the results of HAPO are published.
  • Further NZ information should be collated:
    • To see if potentially different recommendations from HAPO are relevant to our population
    • To see what the impact of any change would be on the number of women diagnosed with GDM and resource implications.
    • To ensure that there are robust models of care that could be expanded to deal with the increase in numbers if any change to criteria was decided.
    • Currently, where NZ criteria for a diagnosis of GDM are not reached, but the 2-hour glucose is 8.0–8.9 mmol/L (the ADIPS-Australia criterion), and the clinician and woman have concerns, it would be reasonable to manage the pregnancy as for GDM.

(3) Should any pregnant women be offered earlier screening for GDM, and if so, who and when?

The issue of early screening (prior to 24–28 weeks’) is complex. Women with Type 2 diabetes have similar pregnancy risks to women with Type 1 diabetes,14 so it is logical to try and identify these women as early as possible during pregnancy. The aim of early screening would be to identify women with hitherto undiagnosed Type 2 diabetes, impaired fasting glucose (IFG), or impaired glucose tolerance (IGT). However, within the pregnancy population, the prevalence of abnormal glucose tolerance is low, so offering early screening to all women is not advocated. Also, the lack of a simple and accurate screening test in early pregnancy remains a difficulty.
The HbA1c may be the most practical test, as it can be performed with booking bloods. One difficulty is that a proportion of women with abnormal glucose tolerance will have an HbA1c within the reference range. The optimal way of identifying these women needs to be determined. The OGTT is currently the diagnostic test for Type 2 diabetes/GDM in early pregnancy.
While women with past GDM or glycosuria should be offered early pregnancy screening, other groups are harder to define but include:
  • Polycystic ovarian syndrome (PCOS).
  • Morbid obesity: (Ethnic-specific31: European=BMI≥35 kg/m2, Polynesian=BMI≥37 kg/m2, Indian and Asian=BMI≥32 kg/m2).
  • Two first-degree relatives with diabetes.
  • Previous unexplained stillbirth.
  • Previous shoulder dystocia.
  • Previous macrosomic baby (≥97th percentile based on customised birthweight chart.32 If there is no access to customised birth weight, ≥4700 g Polynesian, ≥4400 g European, ≥4000 g Asians (including South Asians).
Women with several weaker risk factors may also require early screening.
  • Women with known IGT/IFG or thought to have undiagnosed Type 2 diabetes should have an HbA1c requested at booking and be directly referred to the Diabetes in Pregnancy team for management.
  • Women with a past history of GDM should have an HbA1c requested at booking (even if the postnatal OGTT for this woman was normal). If the result is above the reference range (≥ 6.0%), the woman should be referred immediately to the Diabetes in Pregnancy team. If <6.0%, an OGTT should be undertaken at the earliest opportunity, typically 14-16 weeks. If the OGTT is normal, it should be repeated at 24-28 weeks (or earlier if clinical suspicion occurs).
  • Women who have other high risks of GDM: The current practice of offering a diagnostic OGTT to women considered at sufficient risk of undiagnosed Type 2 diabetes should still continue. Measuring HbA1c as an initial screening test should be formally piloted and assessed to determine its role in this population.

(4) How should care be delivered for women with GDM?

The move to a universal offer of screening for GDM and the possible lowering of diagnostic thresholds for GDM are likely to increase demand for services for women with diabetes in pregnancy. Closer working relationships between the various health professionals involved with the women concerned could mitigate such an increase in demand. An approach to facilitate this is shown in Figure 2.
Figure 2. Proposed framework for care pathway for women with GDM in New Zealand
Recommendations for the provision of care for women with GDM:
  • Care needs to maintain the focus on women becoming mothers, and on the birth of healthy babies, only part of which is the management of their GDM.
  • All DHBs require a defined Diabetes in Pregnancy team.
  • The process for screening for GDM should include:
    • The development and establishment of a programme to increase awareness of GDM in the population.
    • A comment on screening for GDM in general pregnancy information sheets.
    • All Lead Maternity Carers (LMCs) should have access to a Diabetes in Pregnancy team, with an agreed process for referral.
    • The development of a specific information sheet, written with extensive consumer consultation, containing balanced information, in the appropriate languages and at the appropriate educational level. This should be given to, and discussed with, each woman. Information relating to healthy eating and physical activity must be included. Ideally this should be available for women during early pregnancy, as it may guide their diet and activity and reduce later risk of GDM. It can be formally discussed at the time of the offer for a glucose challenge test. The sheet could include a graph of the optimal gestation to screen.
    • Screening being offered at the 24 weeks visit [unless earlier—see issue (3) above], and if agreed, to be completed between 26 and 28 weeks but before the 28-week visit. Offers of screening should incorporate use of the information sheet and it should be documented that informed consent to screen was given by the woman.
    • If the screening result is positive, the woman should be contacted by the person ordering the test to explain the result and refer for an OGTT. This test should be undertaken within one week and include the fasting and 2-hour glucose as a minimum.
    • If the test results indicate GDM, the results will be explained by the person ordering the test, initial action should be initiated and the woman should be referred to the Diabetes in Pregnancy team.
    • An ongoing continuing professional education programme should be provided to support primary care services and facilitate primary care and specialist service integration. Lab staff could be included in this in relation to screening
  • A national ongoing monitoring system that monitors, at the DHB level, the proportion of women being screened, gestation at screening, gestation at OGTT, gestation at referral and gestation at first visit, linking with outcome data, should be in place. A system to ensure that women that have a homebirth are also included in the audit will need to be developed
  • All DHBs should facilitate the local development and definition of a model of care that best suits their region that address the issues/ principles raised in this report particularly:
    • All diabetes in pregnancy, including GDM, is high risk and needs careful monitoring (ultrasound, glucose, clinical).
    • All LMCs should have access to a Diabetes in Pregnancy Team and ultrasound scanning facilities.
    • A close relationship, particularly good communication, is needed between the woman’s primary healthcare team, the diabetes educator and LMC.
    • LMCs, primary healthcare, and the Diabetes in Pregnancy Team in each District should develop agreed standards of care and referral pathways based upon Australasian Guidelines.
    • The ability of midwives to provide dietary advice, glucose monitoring teaching, and management advice about diabetes in pregnancy is not a core competency for midwifery. This does not preclude that women need midwifery care and that some midwives have an interest in this area and will have additional education to provide care for women with GDM in conjunction with the diabetes in pregnancy service in that region.
    • The management of diabetes in pregnancy should be integrated with the woman’s primary healthcare team. This is essential to provide follow-up—e.g. annual/biannual OGTTs for women with past GDM and they may be involved in initiation and community-based aspects of management of GDM.
    • Those caring for women with diabetes in pregnancy need to be alert as the woman’s clinical condition can change rapidly.
    • Those in primary care will need updating and ongoing education about GDM management including pregnancy-specific dietary, glucose monitoring, and overall information advice.
  • Each district should consider participating in the ADIPS audit and benchmarking programme.33 All pregnancies complicated by GDM would be part of the audit programme as a result.


It is important for the Technical Report (including its recommendations) to be seen in the context of a constructive and collaborative response to the current need to address the diabetes epidemic as it impacts on pregnant women. Each participating organisation is reviewing the current situation, and each has its own priorities, whether this be clinical standards, informed consent, cost or other systems issues. We hope that this report places NZ in a position to improve the health of those women and their children affected by GDM.
Competing interests: None known.
Author information: David Simmons, Australasian Diabetes in Pregnancy Society, Hamilton; Janet Rowan, Australasian Diabetes in Pregnancy Society, Auckland; Rosemary Reid, Royal Australian and New Zealand College of Obstetricians and Gynaecologists, Christchurch; Norma Campbell, New Zealand College of Midwives, Christchurch; On behalf of the National GDM Working Party (see Appendix 1)
Acknowledgements: We are grateful to all study participants as well as the Ministry of Health, New Zealand College of Midwives, and Australasian Diabetes in Pregnancy Society for their support. Special thanks to Duanna Fowler for her assistance.
Correspondence: Professor David Simmons, Institute of Metabolic Science, PO Box 281, Cambridge University Hospitals NHS Foundation Trust, Cambridge CB2 0QQ, England. Email:
  1. Hoffman L, Nolan C, Wilson JD, et al. Gestational diabetes mellitus-management guidelines. The Australasian Diabetes in Pregnancy Society. Med J Aust. 1998;169:93–7.
  2. Cheung NW, Byth K. The population health significance of gestational diabetes. Diabetes Care. 2003;26:2005–9.
  3. Simmons D, Gatland BA, Leakehe L, Fleming C. Frequency of diabetes in family members of probands with non-insulin-dependent diabetes mellitus. J Intern Med. 1995;237:315–21.
  4. Simmons D, Wolmarans L, Cutchie W, et al. Gestational Diabetes Mellitus: Time for consensus on screening and diagnosis. N Z Med J. 2006:19:U1807
  5. Agarwal MM, Dhatt GS, Punnose J, Koster G. Gestational diabetes: dilemma caused by multiple international diagnostic criteria. Diabetic Med. 2005;22:1731–6.
  6. Cutchie W, Simmons D, Cheung NW. Comparison of international and New Zealand guidelines for the care of pregnant women with diabetes. Diabet Med. 2006;23:460–8.
  7. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). Statements of the RANZCOG.
  8. New Zealand College of Midwives. Gestational diabetes: NZCoM Consensus statement. NZCOM, Christchurch, New Zealand; 1996.
  9. Jarrett RJ. Gestational diabetes: a non-entity. BMJ. 1993;306:37–8.
  10. Zimmet P, Alberti KGMM, Shaw J. Global and societal implications of the diabetes epidemic. Nature. 2001;414:782–7.
  11. Reilly JJ, Dorosty AR. Epidemic of obesity in UK children. Lancet. 1999;354:1874–5.
  12. Ferrara A, Kahn HS, Quesenberry CP, et al. An increase in the incidence of gestational diabetes mellitus: Northern California, 1991-2000. Obstet Gynecol. 2004;103:526–33.
  13. National Women's Annual Clinical Report 2005. National Women's Health, Auckland District Health Board.
  14. Feig SF, Palda VA. Type 2 diabetes in pregnancy: a growing concern. Lancet. 2002;359:1690–2.
  15. Tuomilehto J, Lindstrom J, Eriksson JG, et al. Prevention of Type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med. 2001;344:1343–50.
  16. Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of Type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002;346:393–403.
  17. Ramachandran A, Snehalatha C, Mary S, et al. The Diabetes Prevention Project shows that lifestyle modification and metformin prevent Type 2 diabetes in Asian Indian subjects with impaired glucose tolerance (IDPP-1). Diabetologia. 2006;49:289–97.
  18. Freinkel N. Banting Lecture 1980. Of pregnancy and progeny. Diabetes. 1980;29:1023–35.
  19. Pettitt DJ, Aleck KA, Baird HR, et al. Congenital susceptibility to NIDDM. Role of intrauterine environment. Diabetes. 1988;37:622–8.
  20. Simmons D, Robertson S. Influence of maternal insulin treatment on the infants of women with gestational diabetes. Diab Med. 1997;14:762–5.
  21. Crowther CA, Hiller JE, Moss JR, et al. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. N Engl J Med. 2005;352:2477–86.
  22. Langer O, Yogev Y, Most O, Xenakis E. Gestational diabetes: the consequences of not treating. Am J Obstet Gynecol. 2005;192:989–97.
  23. Nachum Z, Ben-shlomo I, Weiner E, Shalev E. Twice daily versus four times daily insulin dose regimens for diabetes in pregnancy: randomised controlled trial. BMJ. 1999;319:1223–7.
  24. De Veciana M, Major CA, Morgan MA, et al. Postprandial versus preprandial blood glucose monitoring in women with gestational diabetes mellitus requiring insulin therapy versus preprandial blood glucose monitoring in women with gestational diabetes mellitus requiring insulin therapy. New Engl J Med. 1995;333:1237–41.
  25. National Health Committee. Screening to improve health in New Zealand. Wellington: Ministry of Health; 2003.
  26. Alberico S, Strazzanti C, De Santo D, et al. Gestational diabetes: universal of selective screening. J Met-fetal Neonatal Med. 2004;16:331–7.
  27. Yapa M, Simmons D. Screening for gestational diabetes mellitus in a multiethnic population in New Zealand. Diabetes Res Clin Pract. 2000;48:217–23.
  28. The HDC Code of Health and Disability Services Consumers' Rights Regulation. Wellington: Health and Disability Commission; 1996.
  29. IDF Clinical Guidelines Taskforce. Global guideline for Type 2 diabetes. Brussels; International Diabetes Federation.
  30. HAPO Study Cooperative Research Group. The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study. Int J Gynaecol Obstet. 2002;78:69–77.
  31. World Health Organization. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363:157–63.
  32. McCowan L, Stewart A. Term birthweight centiles for babies from New Zealand’s main ethnic groups. Aust N Z J Obstet Gynecol. 2004;44:432–5.
  33. Simmons D, Cheung NW, Lagstrom J, et al. The ADIPS Pilot National Diabetes in Pregnancy Audit Project. Aust N Z J Obs Gynae. 2007;47:198–206.
Appendix 1. Members of the National GDM Working Party
David Simmons
Norma Campbell
Janet Rowan
Margret Norris
Pat Bent
Barbara Beckford
Lynda Williams
Sandy Dawson
Peter Moore
Cat Wilson
Carol Perwick
Estelle Mulligan
Nimisha Waller
Isabelle White
Jenny Valgrae
Rose Elder
Rosemary Reid
Don Simmers
Kristen Berger
Australasian Diabetes in Pregnancy Society
DHB Maternity Managers Network
Diabetes New Zealand
Federation of Womens’ Health Councils
Maternity Services Consumer Council
Ministry of Health
New Zealand Society for the Study of Diabetes/Physician
New Zealand Society for the Study of Diabetes/Diabetes Nurse Specialist
New Zealand Society for the Study of Diabetes/New Zealand Dietetic Association
Ngā Maia o Aotearoa me Te Waipounamu
NZ College of Midwives
Pacifica Inc.
Parents Centre New Zealand Ltd.
Perinatal Society
Royal Australian and New Zealand College of Obstetricians and Gynaecologists
Royal New Zealand College of General Practitioners
Women’s Health Action
Current issue | Search journal | Archived issues | Classifieds | Hotline (free ads)
Subscribe | Contribute | Advertise | Contact Us | Copyright | Other Journals