True criteria were applied (3). Mission et. al

prevalence of GDM worldwide is unknown. DeSisto et. al (5) carried out a
prospective study between 2005 and 2010 to establish prevalence of GDM across
the United States. They found that GDM prevalence was as high as 9.2%, but
varied depending on local population and diagnostic criteria. Similarly, in
Europe the Atlantic Diabetes in Pregnancy collaborators examined prevalence
using the new IADPSG criteria. They found a prevalence rate of 12.4% compared
to 9.4% when the older WHO criteria were applied
(3). Mission et. al found the IADPSG criteria increased prevalence and
was more expensive but cost effective in improving maternal and neonatal outcomes



Risk Factors for GDM

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are already a number of well-established risk factors for gestational diabetes;
maternal BMI greater than 30, history of macrosomia
(>4.5 kg), previous history of gestational diabetes, family history of
diabetes and ethnicity, including Asian and Filipina women (7). According to current
NICE guidelines women with one or more of these risk factors should be tested
for GDM prior to or at 24-28 weeks of pregnancy. (8)


However, as obesity and diabetes mellitus prevalence increases in the global
community it is becoming more and more difficult to identify high risk women
based on these risk factors alone. With only 6% of pregnancies in CUMH currently
diagnosed with GDM and an estimated national prevalence of 12.4%, it is
reasonable to hypothesise that a number of women are going undiagnosed (1,2).



1.4 Diagnosis of GDM


Gestational diabetes
mellitus is diagnosed by an oral glucose tolerance test, usually taking place
between 24 and 28 weeks’ gestation. There are a number of glucose tests,
ranging from a 50g glucose challenge test (GCT) to a 3-hour 100g oral glucose
tolerance test. Diagnostic criteria vary depending on location with the
diagnostic criteria currently in use in Ireland being the IADPSG criteria (3). The
literature showed a variety of diagnostic criteria in use, with the IADPSG
criteria and ADA criteria being the most common, used in 70% of studies
reviewed. The implementation of a globalised
standard diagnostic criteria, if only within research studies, would be useful
in establishing the true prevalence of GDM and the efficacy of early screening
factors across varying populations.



Prediction of GDM


There has been extensive research into possible markers and
predictive factors for gestational diabetes in recent years. Many studies have
focused on the second trimester but few have produced convincing data on
effective markers in the first trimester of pregnancy.


A number of studies have proven the efficacy of measuring maternal
characteristics in early pregnancy and associated risk of GDM. Mothers who go
on to develop GDM during pregnancy tend to be older, have a higher BMI, higher
blood pressure and a family history of diabetes or GDM (10). These findings
correlate with long established risk factors for GDM (8) and it is with the
addition of biochemical markers to early screening that an increase in
predictive power of GDM can be seen, such as in Theriault et. Al (11). They
described a prediction model for GDM based on HbA1c levels, SHBG level, BMI and
family history of diabetes (type I and type II) and GDM.


In terms of biochemical
markers alone, there has been a lot of research into the association between
early pregnancy vitamin D levels and later development of GDM. Lacroix et. al
(12) measured vitamin D levels in the first trimester and found that women with
GDM had markedly lower vitamin D levels than non-GDM women. 83% of the women
who went on to develop GDM were in the insufficiency/deficiency range in early
pregnancy versus just 74.2% of non-GDM women. The DALI study (Vitamin D
and lifestyle intervention for gestational diabetes mellitus prevention) is a
European multicentre, randomised trial taking place across 9 countries. Women
at increased risk of GDM will be recruited and placed into a variety of
intervention groups with the hope of gaining insight into preventive measures
against GDM in overweight and obese women (13).


relationship between GDM and thyroid hormone levels is also a much researched
area. A number of studies have reported an association between low levels of
fT4 and GDM during the 2nd and 3rd trimesters however
Yang et. al (14) reported first trimester TSH and fT4 levels were significantly
lower in GDM women than in non-GDM women. Similarly, Haddow et. al (15) speculated that increased peripheral
deiodinase activity as a result of increased caloric intake results in weight-related
low levels of fT4, and increased conversion to fT3, which is the hormone
responsible for glucose-related metabolic activity.