The occurrence of fetal CHD in pregnant women with gestational
diabetes mellitus (GDM) is less well documented, but has generally
been thought to be lower than those with pre-existing DM. Gestational
diabetes is defined as ’any degree of glucose intolerance with onset or
first recognition during the present pregnancy’ and can in some cases,
inadvertently include women with pre-existing, undiagnosed DM [6].
International consensus dictates that the diagnosis of GDM is based
on the oral glucose tolerance test, but the threshold for diagnosis and
screening methods vary between professional bodies [7-9]. It is known
to occur in at least 1-5% of all pregnancies and is associated with an increase in perinatal and maternal morbidity [10,11]. The combination
of physiological, lifestyle, ethnic and genetic factors predisposes some
women to develop gestational diabetes mellitus (GDM) [12]. Risk
factors include a previous infant with a birth weight >4kg, maternal
BMI >30, age > 25 years, previous GDM, family history of DM, certain
ethnic groups, essential or pregnancy related hypertension, unexplained
stillbirth/miscarriages and glycosuria. However, there is an absence of
risk factors in approximately 50% of women.