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
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
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
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:
evidence confirming benefits of treating women with GDM;
inter-generational effect of exposure of the fetus to maternal diabetes;
that reduce progression to Type 2 diabetes in high-risk populations;
long-term health benefits for women and their children by identifying and
treating GDM; and
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 www.midwife.org.nz
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
The benefits from screening for GDM are to:
adverse pregnancy outcomes in women subsequently diagnosed and treated for GDM;
risks in subsequent pregnancies by increasing the likelihood of preconceptual
identification and management of undiagnosed diabetes; and to
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.
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'
All women should receive an offer of routine screening
For this to occur, it is crucial that:
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
is written information available about the implications of screening and
diagnosis of GDM that is nationally consistent and easily understood by
are informed about their management options should they be diagnosed with GDM
and remain the central focus of the model of care provided;
are informed about screening in a timely and appropriate way;
is documentation that screening for GDM has been discussed, relevant information
provided to the woman and the woman has consented to screening; and
is a system to ensure that screening for and management of GDM are continuously
assessed, to allow development of further
(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
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.
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
NZ information should be collated:
see if potentially different recommendations from HAPO are relevant to our
see what the impact of any change would be on the number of women diagnosed with
GDM and resource implications.
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.
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
(3) Should any pregnant women be offered earlier screening for GDM, and if so,
who and when?
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
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:
ovarian syndrome (PCOS).
Polynesian=BMI≥37 kg/m2, Indian and
first-degree relatives with diabetes.
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
Women with several weaker risk factors may
also require early screening.
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.
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).
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
Recommendations for the provision of care for women
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.
DHBs require a defined Diabetes in Pregnancy team.
process for screening for GDM should
development and establishment of a programme to increase awareness of GDM in the
comment on screening for GDM in general pregnancy information sheets.
Lead Maternity Carers (LMCs) should have access to a Diabetes in Pregnancy team,
with an agreed process for referral.
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.
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
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
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.
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
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
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
diabetes in pregnancy, including GDM, is high risk and needs careful monitoring
(ultrasound, glucose, clinical).
LMCs should have access to a Diabetes in Pregnancy Team and ultrasound scanning
close relationship, particularly good communication, is needed between the
woman’s primary healthcare team, the diabetes educator and LMC.
primary healthcare, and the Diabetes in Pregnancy Team in each District should
develop agreed standards of care and referral pathways based upon Australasian
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.
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.
caring for women with diabetes in pregnancy need to be alert as the
woman’s clinical condition can change rapidly.
in primary care will need updating and ongoing education about GDM management
including pregnancy-specific dietary, glucose monitoring, and overall
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
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.
Professor David Simmons,
Institute of Metabolic Science, PO Box 281, Cambridge University Hospitals NHS
Foundation Trust, Cambridge CB2 0QQ, England. Email: email@example.com
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