Diabetes in pregnancy develops when the pancreas do not produce sufficient insulin in the setting of hyperglycemia induced by this physiological event. Despite its incompletely understood etiology, early recognition is mandatory in order to reduce the risk of many maternal and fetal complications. Repeated measurements of serum glucose levels are needed to make the diagnosis.
Under physiological circumstances, placental hormones, increased maternal adiposity, increased pancreatic secretion of insulin, as well as several other factors, together induce a state of insulin resistance in the mother midway through pregnancy  . Due to still unknown reasons, some women progress to a state of permanent insulin resistance and develop diabetes in pregnancy.This is described as glucose intolerance that was either unrecognized or absent before pregnancy (the terms pre-gestational diabetes, or overt diabetes are used as well)   . Diabetes in pregnancy affects between 2-5% of all pregnant women, and various risk factors have been established: African American, Hispanic and Asian ethnicity (all predispose to a higher rate of diabetes mellitus type 2), preexisting hypertension, history of unexplained miscarriages and stillbirths, a positive family history for diabetes mellitus, obesity, older maternal age, polycystic ovarian syndrome (POS), macrosomia (birth weight of more than 4000 g) of babies born from previous pregnancies, and of course, prior history of diabetes in pregnancy  . Although not always, the clinical presentation of increased glucose intolerance is practically absent, as the majority of women are asymptomatic . However, numerous maternal and fetal complications are described in the absence of an early diagnosis and adequate therapy. Women who develop diabetes in pregnancy suffer from recurrent urinary tract infections (UTIs) and may develop hypertension, preeclampsia or eclampsia, a life-threatening disorder    . Moreover, the risk of preterm labor is increased as a result of polyhydramnios that frequently develops  . On the other hand, excessive fetal growth resulting in macrosomia is virtually always a complication of GDM, which predisposes fetuses to metabolic abnormalities and injuries during delivery (eg. shoulder dystocia and the frequent need for cesarean delivery), while neonatal metabolic changes (hyperbilirubinemia, hypoglycemia, and respiratory distress) are also common  . In addition to short-term adverse events, diabetes mellitus can persist even after pregnancy, and a high incidence of cardiovascular diseases in mothers has been reported    .
Signs and symptoms of diabetes in pregnancy may not be apparent until delivery or until severe complications occur. For this reason, a thorough patient history is a vital step in assessing risk factors, after which screening methods should be implemented. The debate regarding screening protocols for diabetes in pregnancy is ongoing, with many authors suggesting that apart from low-risk individuals (Caucasian women under 25 years of age, a low body mass index - BMI, and no previous signs of glucose intolerance), serum glucose levels must be evaluated in all pregnant women      . Numerous screening guidelines exist for diabetes in pregnancy, including those created by the National Diabetes Data Group (NDDG), American Diabetes Association (ADA), International Association of Diabetes and Pregnancy Study Groups (IADPSG), American College of Obstetricians and Gynecologists and several other   . However, the criteria formulated by the World Health Organization (WHO), updated in 2013, are most widely accepted. They recommend screening of all pregnant women by conducting an oral glucose tolerance test (OGTT) with 75g of glucose and subsequent serum measurements . If fasting glucose levels are > 5.1 mmol/L or if levels after 1 hour are > 10 mmol/L, or if levels after 2 hours are > 8.5 mmol/L, a diagnosis of diabetes in pregnancy can be made . Serum evaluation of hemoglobin A1c (HbA1C) is also proposed as a diagnostic tool for confirming diabetes in pregnancy, and the cut-off value of ≥48 mmol/mol (6.5%) was accepted as a supportive criterion for this condition .