CHIEF EDITOR’S NOTE: This article is part of a series of continuing education activities in this Journal through which a total
of 36 AMA/PRA Category 1 CreditsTMcan be earned in 2007. Instructions for how CME credits can be earned appear on the
last page of the Table of Contents.
Gestational Diabetes: A Review of the
Current Literature and Guidelines
Martine H. Hollander, MD,* K. Marieke Paarlberg, MD, PhD,†
and Anjoke J. M. Huisjes, MD†
*Resident, Department of Obstetrics and Gynecology, AZ Middelheim, Antwerpen, Belgium; and †Gynecologist,
Department of Obstetrics and Gynecology, Gelre Ziekenhuizen (Hospitals), Apeldoorn, The Netherlands
Despite large numbers of original research studies spanning 4 decades there is still no consen-
sus on the subject of gestational diabetes. Should all pregnant women be screened or only those
with risk factors? Or is it safe not to screen at all? Which screening test and which diagnostic test
are the most reliable? Which cutoff values should we use? What are the risks involved for mother
and baby and can treatment improve outcome? What is the connection between gestational
diabetes and diabetes mellitus type II? Are there disadvantages to screening? A review of relevant
articles shows that definitive answers to these questions are not yet available. There is no gold
standard screening test and no threshold glucose value above which complications are markedly
increased. On the contrary, there appears to be a continuum of slowly increasing risks with rising
blood glucose values, where it seems difficult to draw a clear line between pathology and physi-
ology. Moreover, treatment has thus far not been shown to significantly improve outcome. There
seems to be an indistinct area between the diagnosis of gestational diabetes and diabetes mellitus
type II, where women with risk factors for one are also predisposed to develop the other, thereby
confusing the diagnosis. Finally, the disadvantages to diagnosing and treating women without a
clearly proven benefit seem to be significant. Therefore it seems defensible to suspend all screen-
ing and treatment for gestational diabetes, or at least significantly raise the threshold for making
a positive diagnosis and initiating treatment, until further research has proven a clear benefit.
Target Audience: Obstetricians & Gynecologists, Family Physicians
Learning Objectives: After completion of this article, the reader should be able to summarize that there is
still no worldwide consensus on the diagnosis, management, and adverse effects of Gestational Diabetes
Mellitus (GDM); explain that all methods of screening vary in sensitivity and depend on very strict preparations
for screening; state that there is no agreement on ideal levels of blood glucose to prevent untoward effects;
Gestational Diabetes Mellitus (GDM) is a contro-
versial subject in obstetrics (1–9).GDM is defined as
glucose intolerance that appears or is first recognized
during pregnancy (1) and disappears after delivery.
Disappearance after delivery is especially important,
since previously undiscovered diabetes mellitus Type
II (DMII) is not infrequently mistaken for GDM.
As a recent Cochrane Database meta-analysis
shows, despite large amounts of research in the last
40 years, there is still no consensus on important
issues such as the incidence of GDM, how to diag-
nose it, what, if any, therapy to employ, and the
effect of GDM on maternal and fetal health. One
The authors have disclosed that they have no financial relation-
ships with or interests in any commercial companies pertaining to
this educational activity.
Lippincott Continuing Medical Education Institute, Inc. has
identified and resolved all faculty conflicts of interest regarding
this educational activity.
Reprint requests to: Martine Hollander, Middelweg 19, 2312 KG
Leiden, The Netherlands. E-mail: email@example.com.
Volume 62, Number 2
OBSTETRICAL AND GYNECOLOGICAL SURVEY
Copyright © 2007
by Lippincott Williams & Wilkins
possible explanation for this controversy is the fact
that certain outcome parameters, such as fetal mor-
tality, have become increasingly rare requiring clin-
ical trials of very large size for definitive evaluation.
Furthermore, screening for, and treatment of GDM
have become so routine, that screening and treatment
trials with an unscreened or treated control group
may not be feasible. In daily practice it is difficult to
find “the gold standard” in diagnosis and treatment.
How do you prevent over treatment, or under treat-
ment? What is supported by good evidence and what
In this review we aim to discuss consecutively
GDM diagnosis, incidence, risks, treatment, and per-
tinent international guidelines. We will also make an
effort to recommend a practical approach to diagno-
sis, treatment, and follow up.
We performed a MEDLINE database search with
the words “gestational” and “diabetes” for articles
published in English between 1993 and 2005.
Screening and Diagnosis
Many tests for GDM have been described over the
past decades. A distinction is generally made be-
tween screening tests and diagnostic tests. A screen-
ing test can be performed on either a selective or a
universal basis. Women with a positive screening test
result continue with a diagnostic test, which is more
extensive and demanding. In this way the prevalence
of GDM in women undergoing the diagnostic test is
higher, resulting in a higher positive predictive value.
In general, screening and diagnosis are performed
between 24 and 28 weeks because at this point in
gestation the diabetogenic effect of pregnancy is
manifest and there is sufficient time remaining in the
pregnancy for therapy to exert its effects (10).
Several different screening tests are in use. The
most widely used is screening for risk factors. If,
during the first interview at booking, risk factors are
found to be present, the woman will undergo a diag-
nostic test later in pregnancy. Screening for risk
factors does not appear to be very reliable. The
positive likelihood ratio is only 1.75, meaning that
women with risk factors are only 1.75 times as likely
to have GDM than those without (8). A good screen-
ing test has a positive likelihood ratio of at least 6.
Screening on the basis of risk factors seems to be
inefficient (11). In other words, a diagnostic test only
in women with risk factors will miss many women
with GDM and will unnecessarily subject many
women without GDM to a diagnostic test.
Another screening test which is very widely used,
is the 50 gram Glucose Challenge Test (GCT)
(1,4,5,7,8) wherein the patient drinks a 50 gram
glucose solution at a random time. Then a blood
glucose measurement is taken after 1 or 2 hours, for
which there are different cutoff values. The Ameri-
can Diabetes association recommends a cutoff value
after 1 hour of either 140 mg/dL (7.8 mmol/L), which
is said to identify 80% of women with GDM, or 130
mg/dL (7.2 mmol/L) which should identify 90%
(12). Weiner et al (13) compared the specificity of a
one-hour test using a threshold of either 140 or 150
mg/dL (7.8 or 8.3 mmol/L) to a 2-hour test with a
threshold of 118 mg/dL (6.6 mmol/L) and found that
a 34% reduction in need for a diagnostic test would
be achieved by using the 2-hour cutoff value, lower-
ing the cost per patient identified by $200. Patients
with a positive GCT are eligible for a diagnostic
test. As with screening for risk factors, problems
have also been reported for the GCT: there are
many false-positives (4) and sensitivity is only
86% at best (14).
Other screening tests are fasting blood glucose and
random blood glucose. These tests are popular be-
cause they are easy to perform and not very demand-
ing for the patient, but unfortunately there is lack of
conclusive data documenting the reproducibility,
sensitivity, and specificity of these tests (5). On the
other hand, some studies find that fasting glucose is
reasonably reliable (15), but it appears that some
patients who are later found to have GDM exhibit
elevated blood glucose levels only after a meal, with
normal fasting levels. Furthermore, fasting glucose
is known to be unreliable for predicting macroso-
mia in patients with diabetes mellitus type I (DMI)
or II (16).
Generally used cutoff values (derived from the
screening for DMII) are 126 mg/dL (7.0 mmol/L) for
fasting blood glucose and 200 mg/dL (11.1 mmol/L)
for random blood glucose (5). These are high enough
that a diagnosis of GDM can be made without having
to continue with a diagnostic test. Much lower cutoff
values, starting from as low as 65 mg/dL (3.9
mmol/L) for fasting glucose have been recommended
when screening for GDM (7). Perruchini et al found
that, when using a cutoff value of 85 mg/dL (4.8
mmol/L), an optimum in specificity and sensitivity
was achieved of 76% and 81% respectively (15). It
has to be noted that fasting and random blood glu-
126Obstetrical and Gynecological Survey
cose values in the first half of pregnancy are on
average a little lower than values for nonpregnant
women (17), while in the second half of pregnancy
they are somewhat higher (7).
Other but not very commonly used screening tests
are the glycosylated hemoglobin, capillary blood glu-
cose measurement with a hemocue, breakfast tests,
lunch tests, glycosuria, blood fructosamine, and the
fetal Abdominal Circumference (fetal AC). Glycosy-
lated hemoglobin appears to have a low sensitivity in
pregnancy and is not to be recommended (18). Capil-
lary blood glucose measurements depend very much on
the meter that is used and are generally not very
reliable (19). The breakfast and lunch tests have the
advantage of using a standard test meal instead of an
artificial glucose solution. The results seem to be
reasonably reliable when performed with a standard
(prescribed) meal (7), but have not been extensively
researched and are not widely used worldwide. Gly-
cosuria is notoriously unreliable since 73% of pa-
tients with glycosuria turn out not to have GDM (7),
and blood fructosamine seems to have little value as
a screening test on account of a very low sensitivity
(20). When using the fetal AC as a screening test,
43% of GDM patients will be left undiagnosed (21).
Moreover, the amount of benefit to be achieved from
therapy when macrosomia has already occurred
The “gold standard” for diagnosing GDM has al-
ways been the 100 gram 3 hour Oral Glucose Tol-
erance Test (OGTT). This test was originally used to
diagnose only “ordinary” diabetes (mainly type II)
and has therefore been validated only for that clinical
entity. When the test was first introduced for preg-
nant women it was hoped that it would distinguish
those who were susceptible to contract DMII later in
life, in order to be able to initiate early treatment. It
was not meant to be used to prevent complications
during the pregnancy itself (22). The conditions for
this test are very strict, and they do not represent a
normal situation in day to day life: during the 3 days
preceding the test the patient must have an intake of
at least 150 grams of carbohydrates per day, and
between 8 and 14 hours before the test is performed
she is not allowed to eat or drink, except for water.
No smoking is allowed during the 12 hours preceding
the test. Before the first (fasting) glucose measure-
ment the patient must rest for 30 minutes. After the
first measurement, the patient drinks a 100 gram
glucose solution. She has to finish this within the
time limit of 5 minutes. One, 2 and 3 hours after
finishing the drink, blood glucose measurements are
taken. During these hours the patient is not allowed
to smoke or walk. After the last measurement is
taken, the patient has to eat something to prevent
The original diagnostic cutoff values according to
O’Sullivan and Mahan (23) were based on measure-
ments in venous blood. Today blood glucose mea-
surements are predominantly performed on plasma.
The O’Sullivan criteria have therefore been con-
verted to measurement in plasma; however, there are
2 separate conversions currently in use: the “Carpen-
ter and Coustan (C&C) conversion” (24) and the
“National Diabetes Data Group (NDDG) conver-
sion” (22) (Table 1).
Various threshold values for the diagnosis of GDM
Fasting 1 Hour2 Hours 3 Hours
100 gm OGTT
100 gm OGTT
75 gm OGTT
75 gm OGTT
75 gm OGTT
95 mg/dL or
105 mg/dL or
126 mg/dL or
95 mg/dL or
95 mg/dL or
180 mg/dL or
190 mg/dL or
155 mg/dL or
165 mg/dL or
140 mg/dL or
155 mg/dL or
160 mg/dL or
140 mg/dL or
145 mg/dL or
180 mg/dL or
190 mg/dL or
Cutoff values for the different diagnostic tests.
Reference numbers appear in parentheses.
C&C indicates Carpenter and Coustan; NDDG, National Diabetes Data Group; WHO, World Health Organisation; ADA, American
Diabetes Organisation; CDA: Canadian Diabetes Association.
Gestational Diabetes Y CME Review Article127
Two abnormal values are needed for the diagnosis
of GDM (23). In the study by Magee et al (25), there
was a significant difference (up to 50%) in reported
incidence of GDM, depending on which of the 2
conversions was used, while there was no discern-
able difference in perinatal outcome.
The biggest problem with this gold standard is that
it is, in fact, not a gold standard at all. Reproducibil-
ity has been reported to be at best 78% (26). One
cause for this could be limited compliance by the
patient, because the test conditions are so strict.
There has been movement to a lower glucose load.
At present, the most commonly used OGTT interna-
tionally is the 75 gram glucose solution. This is the
test recommended by the WHO (17) and it is used
mainly outside the United States (Europe, Japan). In
the United States the 100 gram OGTT is still pre-
dominantly used (Table 2).
Guidelines and recommendations of some major European and North American professional organisations concerning testing
Cochrane Database (9)2002—— Not enough data to
prove benefit of
— 75 gm OGTT at 24–28 weeks
If ?130 mg/dL (7.2 mmol/L)
or ?140 mg/dL (7.8mmol/L):
100 gm OGTT
50 gm GCT Test everyone or only
in case of risk fac-
tors, but 90% have
— ADA (12)2002 In case of risk factors 50 gm
Same as ACOG
USPST (4) 2003— Test everyone or only
in case of risk fac-
tors, no recommen-
dation on which is
— Fourth International Workshop-
Conference on Gestational
Diabetes Mellitus (86)
Canadian Taskforce on the
Periodic Health Examination (87)
1998 In case of risk factors: 50 gm
GCT or 75 gm OGTT for all
Same as ACOG
for or against uni-
versal screening, no
CDA (85) 1998 In case of risk factors 50 gm
In case of risk factors 50 gm
100 gm OGTT
SOGC (5)2002100 gm OGTT if ?110 mg/dL
(6.1 mmol/L): 75 gm OGTT
The option not to
screen or treat is
Urine for glucose at
every visit to check
Diabetes UK (7)?Random glucose at booking
and at 28 weeks
SIGN (7)?Urine for glucose and random
glucose at every visit
Assessment UK (7)
200250 gm GCT at 24–28 weeks,
if ?140 mg/dL (7.8 mmol/L)
screening based on
age, obesity and
European Association for the
Study of Diabetes (88)
199150 gm GCT (?148 mg/dL or
8.2 mmol/L) and fasting
glucose (?85 mmol/dl or
75 gm OGTT, cut-off fasting
100 mg/dL (5.5 mmol/L)
and 2-hours 162 mmol/dL
Reference numbers appear in parentheses.
WHO indicates World Health Organisation; ACOG, American College of Obstetricians and Gynecologists; ADA, American Diabetes
Organisation; USPST, United States Preventive Services Taskforce; CDA, Canadian Diabetes Association; SOGC, Society of Obste-
tricians and Gynecologists of Canada; SIGN, Scottish Intercollegiate Guidance Network.
128 Obstetrical and Gynecological Survey
As for the original 100 gram OGTT, different
cutoff values are in use for the 75 gram OGTT
(Table 1). Unfortunately, this test is also said to be
not very reproducible (7). The same holds true for
the 50 gram OGTT which is used in some Austra-
lian hospitals (27).
Another commonly used test is the glucose day curve
(GDC), in which several measurements are taken at
fixed intervals during the day (after meals), without
prescribing any specific meal or glucose load. The most
widely used cutoff values with this test are 100 mg/dL
(5.5 mmol/L) for fasting and 126 mg/dL (7.0 mmol/L)
for random blood glucose. The GDC is predominantly
used for evaluating the effects of therapy for GDM, but
can also be used as a diagnostic test.
Lately, abnormal test results on any diagnostic test
have been more and more divided into 2 groups:
impaired glucose tolerance (IGT) and “true” GDM.
The theory is that most differences in maternal and
perinatal outcome can be attributed to the rela-
tively small number of women with significantly
elevated blood glucose levels, whereas the large
majority of women with marginally or moderately
elevated levels have little or no increased risk of bad
outcome at all (17). Cutoff values for the 75 gram
OGTT to distinguish between the 2 groups are a 2
hour value of between 140 and 200 mg/dL (7.8–11.0
mmol/L) for IGT, and 200 mg/dL (11.1 mmol/L) or
more for GDM.
The exact incidence of GDM is unknown. The
percentages reported in the literature are variable,
and depend very much on the characteristics of the
population studied and the criteria used for the diag-
nosis. Ethnic origin and age seem to be especially
important factors. One prospective observational
study (28) divided the population into 2 groups based
on the presence or absence of risk factors. The in-
vestigators arrived at an incidence of 2.4% in the
low risk group and 3.2% in the high risk group,
which was not a significant difference. When the
population was divided into groups based on eth-
nic origin the incidence of GDM was 0.4% for
Caucasian women, 1.5% for Black women, 3.5%–
7.3% for Asian women, 4.4% for women from the
Indian subcontinent, and as much as 16% for Native
The reported incidence of GDM increases with
maternal age: most studies have used 25 years as
cutoff point. The incidences found were 0.4%–0.8%
in women younger than 25 years and 4.3%–5.5% in
women older than 25 years (11,29,30).
When incidence is studied by country of origin, the
United States report 3%–8% (31), with a trend of
rising percentages in more recent publications. The
United Kingdom reports an incidence of 2% (7) and
Canada describes 3.8% (32). The rising percentages
in reported GDM may well be correlated with an
epidemic of obesity in developed countries (2), es-
pecially in the United States. Another explanation for
the increase in incidence in the United States could
be the trend to lower cutoff values for diagnostic
tests, or greater uptake of the screening tests.
Many risk factors for GDM have been suggested.
Therefore, most screening strategies for GDM make
use of the presence or absence of risk factors. The
risk factors most widely used are:
• Age over 25 (2,4–7) or 30 (33) years old. This
risk factor is used throughout the world and
most countries use 25 years as a threshold.
• Body mass index (BMI) over 25 (34) or 27 (35).
• Ethnic origin, generally interpreted to mean any
non-Caucasian women (2,4–7).
• DMI or II or GDM in a first degree relative
• Previous history of GDM (36).
Less commonly mentioned risk factors are a wom-
an’s own birth weight being lower than 2500 grams
(37) or below the 10th percentile (38), a previous
macrosomic baby (2,5), a previous bad outcome of
pregnancy, for instance stillbirth (2,5), and polyhy-
dramnios and/or a suspected LGA fetus in the current
Depending on which risk factors are used to select
women to be tested for GDM, a maximum of 90% of
women are deemed to be high risk (4). If screening
were based on the following risk factors: age over 25
years old, and/or BMI over 27, and/or non-Caucasian
origin and/or positive family history for GDM or
DM, Davey et al (40) found that only 0.6% of women
with GDM would go undiagnosed. On the other
hand, depending on the risk factors used, several
other studies reported that when screening only
women with risk factors for GDM, up to 43% of
women with GDM would not have been diagnosed
Therefore, it seems that predisposing factors for
developing GDM are not helpful in developing a
screening policy, especially considering the fact that
Gestational Diabetes Y CME Review Article 129
the average age of pregnant women has risen quite
significantly since the time most of the cited studies
were carried out.
Risks of GDM for Mother and Fetus
The purpose of screening for GDM is to diagnose
and treat patients as early in pregnancy as possible,
thereby preventing complications possibly caused by
elevated blood glucose levels in pregnancy. A num-
ber of pregnancy complications are thought to be
caused by GDM.
Macrosomia is one of the most commonly men-
tioned problems associated with GDM (1,4–9).
However, not every study uses the same criteria for
macrosomia. Many authors use a cutoff value for
birth weight above the 90th percentile (9) or a birth
weight of more than 4000 grams for macrosomia, but
some use 4500 grams (42).
The reported incidence of macrosomia (?4000
grams) in women with GDM is 16%–29% (43,44), as
opposed to a 10% rate in women without GDM. On
the other hand, GDM can not be the only factor
responsible for macrosomic babies, since Spellacy et
al (42) found that, of all the babies with a birth
weight higher than 4500 grams, only 5% had a
mother diagnosed with GDM. Another study reports
that only 10% of all babies with a birth weight over
4000 grams had a mother with GDM (45).
Casey et al (46) also concluded that a maximum of
12% of macrosomia could be explained by maternal
GDM. The rest was due to maternal age, weight, and
Macrosomia is an intermediate outcome, which in
itself is not damaging to mother or baby. However,
with macrosomia there might be an increase in ce-
sarean deliveries, instrumental deliveries (forceps
and ventouse deliveries), birth trauma such as bra-
chial plexus injury or clavicular fracture, or neonatal
Therefore, most authors mention an increase in
cesarean deliveries as one of the most important
complications of GDM. However, this may simply
be a labeling effect: because a patient has been di-
agnosed with GDM the threshold for cesarean deliv-
ery may be lowered. Naylor et al (43) reported a
cesarean rate of 30% in women with GDM, com-
pared to 20% in controls in spite of the fact that
treatment of the GDM had normalized birth weights.
Shoulder Dystocia and Birth Trauma
The increase in birth trauma in the offspring of
women with GDM is thought to be caused by a
higher rate of macrosomia, which predisposes to
shoulder dystocia. Since shoulder dystocia is not in
itself harmful to mother or baby, the discussion
mainly revolves around its consequences, namely
clavicular fractures and brachial plexus injuries.
The incidence of brachial plexus injury has been
shown to be increased with increasing birth weight,
operative vaginal delivery and the presence of glu-
cose intolerance (47). However, Perlow et al (48)
found in a retrospective chart review that GDM was
present in the mother in only 6% of the brachial
plexus injuries. Furthermore, they report that in 84%
of clavicular fractures no mention of shoulder dys-
tocia was made in the medical records.
A brachial plexus injury is a very serious compli-
cation and can have permanent sequelae in 5%–22%
of cases (49). At the moment, this is one of the
leading causes of malpractice allegations. However,
the concept of prophylactic caesarean delivery as a
means to prevent shoulder dystocia and therefore
avoid brachial plexus injury has not been supported
by either clinical or theoretic data (50). Rouse et al
calculated in 1996 that, in diabetic women, 443 ba-
bies with an estimated birth weight over 4500 grams
or 489 babies with an estimated birth weight over
4000 grams would have to be delivered by elective
cesarean delivery to prevent one permanent brachial
plexus injury. This would have then cost $930,000 or
$880,000, respectively, for each case prevented (51).
Therefore, although for an individual patient with a
permanent brachial plexus injury a planned caesarean
could have made a large difference in quality of life,
for the population in general the benefits likely do
not outweigh the disadvantages.
Neonatal Metabolic Problems
In GDM an increased rate of neonatal hypoglyce-
mia, hyperbilirubinemia, hypocalcemia, and polycy-
themia is reported (52). This is then said to cause an
increase in admission to the Neonatal Intensive Care
Unit (NICU). In a study by Jensen et al (53) an
increased rate of hypoglycemia is reported of 24% in
babies of mothers with GDM compared to 0% in
negative controls. However, this was a retrospec-
tive study and could be suffering from bias, as
130Obstetrical and Gynecological Survey
children of mothers with known GDM are much
more likely to be tested for hypoglycemia than
asymptomatic children of mothers without GDM.
Furthermore, there is evidence that neonatal hypo-
glycemia is much more related to macrosomia per se
than to maternal GDM (54).
The most important question is: do these metabolic
problems really have any permanent negative conse-
quences for the babies’ long-term health? It appears
that adequately treated hyperbilirubinemia probably
has no lasting effects on the infant (55). In addition,
long-term damage due to neonatal hypoglycemia
seems limited to those few cases with hypoglycemic
seizures or recurrent hypoglycemia (56). On the
other hand, there are definite drawbacks to screening
all asymptomatic babies of GDM mothers for meta-
bolic disease: the inconvenience for staff and baby of
repeated blood tests, the costs of these tests and the
separation between mother and child due to an un-
necessary admission to the NICU.
Perinatal mortality was originally considered to be
the most important complication of GDM. Evidence
to support this is mainly found in older literature
(57). However, these studies described relatively
small numbers of patients and the difference was
found only in patients over 25 years of age. Further-
more the increase in mortality was not affected by
treatment of GDM. More recent and larger trials have
not been able to confirm this increase (46). To be
able to find or rule out a significant difference in
perinatal mortality between babies of mothers with
GDM and negative controls, larger numbers of pa-
tients would need to be included in randomized trials.
GDM has been associated with an increase in hy-
pertensive disorders but there is some inconsistency
in this association and questions about whether it is
causal in nature. One study found a 20% incidence of
hypertensive disorders in GDM women compared to
11% in controls (53). In contrast, Naylor et al, in the
Toronto Tri-Hospital Gestational Diabetes Project,
found only a 9% incidence of preeclampsia in un-
treated GDM (43), which is comparable to the inci-
dence reported in treated women with GDM and in
women treated for DMII or type I Diabetes Mellitus
(DMI) (58). Therefore, treatment of GDM apparently
does not reduce the incidence of hypertensive disor-
ders in pregnancy. None of the trials mentioned above
had corrected for age or maternal BMI, which are well
established risk factors for hypertensive disorders in
pregnancy. It seems more likely, then, that any in-
crease in hypertension in GDM patients could be
accounted for by the fact that their age and BMI
predispose them to GDM as well as hypertension.
Other Complications Associated with GDM
It is unclear whether premature delivery is more
common among women with GDM (4). The same
holds true for third- and fourth degree perineal tears
(59). These complications are reported only rarely in
articles dealing with GDM and the influence of GDM
on their incidence is difficult to ascertain.
The strongest associations between GDM and ad-
verse outcomes for mother and baby, i.e. perinatal
mortality, macrosomia, hypertensive disorders, and
cesarean sections, are found in a subgroup of women
with extremely high blood glucose values (75-gram
2-hour glucose ?200 mg/dL or 11.1 mmol/L) (60).
In a group of women with lower blood glucose
values (75-gram 2-hour values of 145–200 mg/dL or
8.0–11.1 mmol/L), classified as IGT, Nasrat et al
(61) did not find any differences in adverse outcomes
between GDM women and negative controls, espe-
cially no difference in the incidence of macrosomia,
neonatal hypoglycemia, and polycythemia.
Late Effects of GDM on Mother and Baby
The prevalence of DMII in women previously di-
agnosed with GDM is higher compared to those
without GDM in their earlier pregnancies (23). Cata-
lano et al (62) found that 22% of women who had
GDM still had elevated blood glucose levels at 6
weeks post delivery. The reported prevalence of
DMII later in life for GDM women varies from 9% in
Caucasian women to 25% in Asian women, 47% in
Hispanics, and as much as 70% in Canadian aborigi-
In a follow up study in a population of Hungarian
women Tamas et al (3) found a prevalence of DMII
of 42% eight years post delivery. An additional 7%
had glucose intolerance. The risk was found to be
higher in women for whom it had been deemed
necessary to prescribe insulin during their pregnancy.
However, women who have been previously diag-
nosed with GDM are much more likely to be tested
for DMII in later life, so that screening bias could be
There is no evidence that treating GDM in preg-
nancy decreases the risk of later developing DMII.
Gestational Diabetes Y CME Review Article131
However, the children of mothers with GDM are also
at risk for DMII and obesity later in life (66). Occa-
sionally an increased risk for neuropsychological
problems has been reported in these children (67).
As mentioned before, there is substantial contro-
versy surrounding the criteria for diagnosing GDM.
There is somewhat more consensus about the appro-
priate treatment once diagnosis is made.
The first step is usually a diet prescribed by a
dietician. The goal is to limit intake of carbohydrates
to 35%–40% of daily caloric intake. In patients with
a BMI over 30 the target is to lower caloric intake by
30%–33% to about 25 kilocalories per kilogram of
body weight (1). The danger of limiting caloric in-
take too much is ketosis in the mother, which for her
child has been associated with psychomotor retarda-
tion and low IQ (67). Furthermore, the patient is
advised to exercise more (68).
If diet and exercise have not resulted in acceptable
blood glucose levels, insulin is commonly pre-
scribed. There is some consensus about the glucose
levels above which insulin therapy is initiated. It is
generally accepted to use the cutoff values recom-
mended by the American Diabetic Association
(ADA) (12): fasting 105 mg/dL (5.8 mmol/L), 1 hour
after a meal 155 mg/dL (8.6 mmol/L) and 2 hours
after a meal 130 mg/dL (7.2 mmol/L). Some studies
recommend starting insulin therapy when the fetal
AC measured by ultrasound is higher than the 75th
percentile for gestational age (69).
However, the target range for blood glucose values
with insulin therapy is very narrow. In a study by
Langer et al (70), the incidence of macrosomic ba-
bies rose with random blood glucose values above
104 mg/dL (5.7 mmol/L), whereas the chance of
Small for Gestational Age (SGA) babies increased
with levels lower than 87 mg/dL (4.9 mmol/L), leav-
ing a very small therapeutic margin.
The use of oral glucose lowering agents is cur-
rently being studied. Most of these can pass through
the placenta and are therefore not deemed safe for
use in pregnancy (12). However, glyburide, an oral
glucose lowering agent often used in the treatment of
DMII, has been shown not to pass through the pla-
centa and has been tested on pregnant women. So far,
it appears safe for use in pregnancy (71), but consid-
ering the limited amount of evidence accumulated to
date its use is not yet being recommended (6). In one
study it had a similar effect as insulin on blood
glucose concentrations (72).
Obviously, the ultimate therapy for GDM is deliv-
ery. Some authors advise induction of labor around
38 to 39 weeks in GDM patients using insulin, which
in one study lowered the risk of shoulder dystocia
from 10% to 1.4% (73). A recent Cochrane Database
meta-analysis, however, found a similar percentage
of shoulder dystocia in the induction groups and the
expectant management groups (74).
Some studies recommend a cesarean delivery for
women with GDM with an estimated fetal weight of
more than 4000 or 4500 grams (51), or more than 5000
grams(42).However,a recent cost-effectiveness anal-
ysis showed that in general, expectant management is
the preferable approach, irrespective of estimated
fetal weight (75).
Does Treatment Improve Outcome?
The effect of treatment of GDM is the subject of a
recent meta-analysis in the Cochrane Database (9).
However, only 3 studies were included, due to very
strict methodological criteria for inclusion. Of
these 3 studies, 2 compared diet alone to diet and
insulin and only 1 compared any treatment to no
treatment at all.
In the meta-analysis, no difference in outcome was
found regarding the percentage of cesarean sections,
NICU admissions or the incidence of macrosomia
(fetal weight greater than the 90th percentile). In
treated patients, a relative risk (RR) of 0.55 (95%
confidence interval (CI) 0.19–1.61) for macrosomia
was observed, but this difference was not significant.
The only statistically significant difference between
the treatment groups and the control groups was a
lower incidence of neonatal hypoglycemia in the
treatment group, RR 0.25 (95% CI 0.07–0.86).
However, when only taking into consideration the
study by Langer et al (76) which compared diet
and/or insulin with no treatment at all, the treatment
group did show a significant reduction in macro-
somic babies (RR 0.27, 95% CI 0.09–0.76) in addi-
tion to the aforementioned reduction in neonatal
hypoglycemia (RR 0.13, 95% CI 0.02–0.97). There
was no observed difference in the number of ce-
sarean sections (RR 0.82, 95% CI 0.36–1.84) or in
the number of admissions to the NICU (RR 0.57,
95% CI 0.18–1.86).
Although these parameters were not included in the
Cochrane meta-analysis, treatment of GDM has not
been shown to reduce perinatal mortality (9) or the
incidence of preeclampsia (5).
An eagerly awaited study was the Australian Car-
bohydrate Intolerance Study in Pregnant Women
132Obstetrical and Gynecological Survey
(ACHOIS) trial (77), which would finally answer the
question whether there is a clear benefit to treatment
of GDM over expectant management. Unfortunately,
there is some concern about how women participat-
ing in this trial were selected. Results were collected
over 10 years in 18 different hospitals, resulting in
only 5 patients per hospital per year. Therefore, some
selection bias may be present. Also, screening was
not evaluated as part of the trial. This means that all
women were screened and only those who met the
criteria for GDM were randomized, so no women
were left unscreened and therefore undiagnosed and
there was no healthy control group.
Regrettably, the authors have yet again counted the
occurrence of shoulder dystocia as a serious compli-
cation in itself, making the difference between the
intervention group (7/506 serious complications) and
the control group (23/524 serious complications)
only just significant (P-value 0.04). Shoulder dysto-
cia by itself should not be considered as an outcome
parameter per se. There are no strict criteria for the
definition of shoulder dystocia, and it is only the
potential sequelae of shoulder dystocia, such as birth
trauma, which matter. When we neglect shoulder
dystocia as an outcome parameter in this study and
look separately at outcome parameters such as the
occurrence of birth trauma like bone fracture (0/506
versus 1/524, P-value 0.38) or nerve palsy (0/506
versus 3/524, P-value 0.11), two of which were in the
same child, and perinatal death (0/506 versus 5/524,
P-value 0.07), the difference between the two groups
is no longer significant (0/506 versus 6/524 serious
complications, P-value ?0.06). Moreover, a substan-
tially greater number of children in the treatment
group were admitted to the NICU (357/506, 71%)
compared to the control group (321/524, 61%), and a
significantly larger number of women in the treat-
ment group underwent an induction of labor (189/
490, 39% versus 150/510, 29%), illustrating that the
diagnosis and treatment of GDM may increase inter-
vention without demonstrable benefit.
In conclusion, no randomized controlled clinical
trial of sufficient sample size has been able to dem-
onstrate conclusively that treatment of GDM (with
diet and/or insulin) improves the outcome of preg-
nancy for mother or fetus. Most studies have method-
ological flaws or are too small to prove a significant
difference. The only confirmed effect of treatment is a
decrease in the incidence of neonatal hypoglycemia,
with unclear importance for the baby’s long-term
Disadvantages of Diagnosis and Treatment
As stated previously, it is unclear whether screen-
ing for and treating GDM is beneficial. Nonetheless,
this is considered standard practice all over the
world. In the United States, at least 94% of gynecol-
ogists test all pregnant women for GDM (78), with-
out first screening for risk factors first. In Canada
testing is also commonly performed, with 84% test-
ing all pregnant women (5). The other 16% (mainly
in the Hamilton area), have suspended all screening
practices and treatment, while awaiting definitive
research. Percentages are significantly lower in the
United Kingdom, where only 17% of the obstetrical
caregivers screen all pregnant women, while 72%
only test those with risk factors. Eleven percent have
suspended all screening practices for the time being.
A telephone enquiry among all Dutch obstetric
units (n ? 93), performed by the authors, shows that
66 units only test women with risk factors (with
different tests). Eight units screen all patients at
booking and those with risk factors are tested again
later in pregnancy. Seventeen units screen all preg-
nant women at 24–28 weeks. In addition, 2 units are
divided about screening practices and each gynecol-
ogist practices by his or her own protocol.
Considering the fact that no clear benefit of screen-
ing for and treating GDM has been proven to date,
the question must be: are we doing more harm than
good? There are several studies reporting a more
negative perception of their own health by women
diagnosed with GDM (79), or even by those who
only had a false-positive screening test (80), although
other studies were unable to confirm this difference
(81) or found a positive effect on mental wellbeing
by a positive test for GDM (77). The diagnostic tests
(OGTTs) themselves are very demanding for the
patients: up to 1.4% of women report vomiting dur-
ing the 75 gram OGTT (82), which rises to 4% for
the 100 gram OGTT (83). Other negative conse-
quences of the diagnosis of GDM and subsequent
treatment are: more medical interventions, for in-
stance more cesarean deliveries (43), ketosis after
dieting (too strictly), which can cause more psy-
chomotor development problems in the children (67),
more SGA babies by too strict use of insulin (70) and
of course higher public health costs.
Brody et al (4) calculated that, with an estimated
incidence of GDM of 4% and treatment with insulin
for 30% of these women, 8900 women have to be
screened to prevent one brachial plexus injury, which
in the majority of cases has no permanent sequelae.
Gestational Diabetes Y CME Review Article133
Gestational diabetes was recognized and treated as a
clinical entity, long before the principles of evidence-
based medicine were developed (84). In light of the
recent scientific developments concerning trial pro-
tocols and interpreting their results it might be time
to re-evaluate the approach to GDM and to adjust our
protocols to current insights. Most of the recent re-
view articles agree that 1) there is no consensus on
whom to test, 2) there is no diagnostic gold standard
and most tests are only moderately reproducible, 3)
the risks of GDM for mother and baby are fairly
minimal, and 4) the benefit of treatment for mother
and baby is uncertain at best. There appears to be a
continuum of slowly increasing risks with rising
blood glucose values. The issue is likely to be further
clouded by the fact that most trials concerning GDM
do not screen for DMII at booking. Therefore, it is
well possible that those women who have the worst
outcome (and very often the most abnormal diagnos-
tic tests) have in fact type II diabetes, predating their
It is difficult to make a clear recommendation
regarding GDM without definitive data from well
done randomized studies indicating benefit. Cur-
rently underway is the Hyperglycemia and Adverse
Pregnancy Outcome (HAPO) trial, financed by the
National Institutes of Health, USA, which will com-
pare treatment to expectant management.
At this time it seems justified to follow the advice
of the Cochrane Database and suspend all screening
and treatment except as part of a clinical study, while
awaiting definitive data from large randomized con-
trolled clinical trials.
Alternatively, it seems safe to adopt much higher
cutoff values for treatment than used to date, as
recommended by Health Technology Assessment
UK (7), thereby treating only real diabetes and not
IGT, considering the evidence for an association of
unfavorable maternal and fetal outcomes with espe-
cially high blood glucose levels.
Also, there seems to be a clear benefit to using
pregnancy as an early metabolic marker for the pre-
disposition to develop DMII. Women who have been
diagnosed with abnormal glucose levels during preg-
nancy should be offered screening for DMII on a
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