Can J Diabetes 43 (2019) 547–548
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Canadian Journal of Diabetes
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Note From the Editors
Diagnosis of Gestational Diabetes: More Questions Than Answers
The entity of gestational diabetes (GDM) has been acknowledged 75-g glucose tolerance test. After 2015, the criteria were changed,
since the 1950s, but the role of screening and the criteria for diag- and clinicians used the 1-step IADPSG criteria (fasting, 5.1 mmol/L;
nosis of GDM continue to be controversial to the present day. Several 1 hour, 10.0 mmol/L; 2 hours, 8.5 mmol/L). Pouliot et al found
very basic questions remain regarding the screening and diagnosis of that changing to the new criteria led to a significant rise in GDM
GDM that have yet to be fully resolved. What criteria should we use incidence, from 10.8% to 17.6%. Although women diagnosed using
to diagnose GDM? Do we need a screening test? When in pregnancy the IADPSG criteria had a higher early pregnancy body mass index
should we diagnose and treat GDM? How do we differentiate GDM (26.3 vs 25.5, p¼0.01), and higher rates of chronic hypertension
from newly discovered pre-existing type 2 diabetes (T2D) in preg- (3.7% vs 1.2%, p<0.0001), they had lower rates of pre-eclampsia,
nancy and how important is it to do so? labour induction and offspring admission to the neonatal intensive
What criteria should we use to diagnose GDM? The diagnosis of care unit. Does this mean the new criteria are better? One may
GDM has evolved from the initial use of criteria developed to pre- wonder whether these improved outcomes were due to the inclu-
dict the development of T2D within 8 years postpartum (1) to the sion of women with milder disease, who may or may not need to
use of criteria based on adverse neonatal outcomes, as defined by be treated. This point was illustrated in a study by Sacks et al (8).
the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study In their work, the authors compared pregnancy outcomes in women
(2). The HAPO study demonstrated that there is no definite glucose who were untreated but met the criteria for GDM only by the
inflection point above which the incidence of adverse outcomes IADPSG criteria, but not the Diabetes Canada criteria, to those who
increases, but rather it is a continuum of risk. More recent data were untreated but met the Diabetes Canada preferred criteria.
have suggested differential outcomes in offspring exposed Women with more severe GDM were treated and excluded. When
throughout gestation to pre-existing T2D compared to GDM with compared to women without GDM, the authors found that women
respect to child-onset obesity and dysglycemia (3). Therefore, there who met the criteria for GDM according to Diabetes Canada had a
continues to be great controversy regarding how to diagnose GDM significantly higher risk of pre-eclampsia, preterm birth, shoulder
and where to place that diagnostic cutpoint. Should we diagnose dystocia and infants who were large for gestational age or had tran-
GDM using the criteria of the International Association of Diabetes sient tachypnea or neonatal hypoglycemia. Women who met the
in Pregnancy Study Group (IADPSG) (4,5)? These criteria define IADPSG criteria had an increased risk of large-for-gestational-age
GDM as one or more: fasting and 1- and 2-hour glucose values dur- infants, but had none of the other more serious adverse outcomes.
ing a standard 75-g oral glucose tolerance test at which the odds for Given these results, one must decide whether it is worth treating
adverse outcomes in offspring (including birthweight, percent the many additional women who would be diagnosed using the
body fat and cord blood C peptide) were 1.75-fold higher than those IADPSG criteria, given their milder disease. A large randomized trial
whose blood sugars were at or below the mean for those time- comparing treatment of women meeting both of these criteria
points. Alternatively, should the cutpoints that reflect 2.0 times would help to answer this question, preferably with an accompa-
the risk be adopted, as the Diabetes Canada recommendations pre- nying cost-effectiveness analysis.
fer (Diabetes Canada Clinical Practice Guidelines)? Given that both One of the other reasons given for choosing the IADPSG criteria is
were derived by consensus, either seems justified. Several coun- based on the finding from the HAPO follow-up study (9) showing
tries were early adopters of the criteria established by the IADPSG. that GDM, as diagnosed by the IADPSG criteria and left untreated,
However, evidence for use of these criteria is still insufficient. leads to an increase in childhood obesity in offspring compared
First, although adverse outcomes were associated with the with offspring of women with normal glucose levels, even after con-
IADPSG criteria, there was no demonstration that their application trolling for many confounders, including maternal body mass index.
would lead to improved outcomes compared with other criteria. Although this shows that untreated hyperglycemia is harmful to
Second, one should be fairly certain of the evidence for their use offspring, questions persist. It remains unknown whether a differ-
since adoption of these criteria leads to a significant increase in ence in childhood outcomes would be apparent at different cut-
the incidence of GDM. In the HAPO trial, utilizing these criteria points and if treatment would reduce these outcomes. It is known,
resulted in an incidence of GDM of 18% compared with the current however, that identification and treatment of women with mild
incidence of 5.6% in Ontario (6). In this issue, Pouliot and col- GDM during pregnancy has no discernible impact on subsequent
leagues report a retrospective cohort study comparing the inci- maternal diabetes, metabolic syndrome or obesity at 7 years after
dence of GDM and pregnancy outcomes using 2 different delivery (10). These are important issues for future research.
diagnostic criteria (7). Before 2015, they used the current Using a completely different approach to diagnosis, in this issue
preferred diagnostic cutpoints (at least 1 of the following: fasting, of the Journal, Ardilouze et al (11) compare use of the Canadian
5.3 mmol/L; 1 hour, 10.6 mmol/L; 2 hours, 9.0 mmol/L) after a “preferred” approach to simply doing self blood glucose monitoring
1499-2671/Ó 2019 Canadian Diabetes Association.
The Canadian Diabetes Association is the registered owner of the name Diabetes Canada.
https://doi.org/10.1016/j.jcjd.2019.09.006
