Gestational Diabetes
المؤلف:
Marcello Ciaccio
المصدر:
Clinical and Laboratory Medicine Textbook 2021
الجزء والصفحة:
p430-432
2025-11-29
109
Gestational diabetes mellitus (GDM) is classically defined as a condition of impaired glucose tolerance of variable degree and severity that occurs during pregnancy (usually in the second or third trimester) and generally regresses after delivery. However, it can recur at a distance, preferentially with the characteristics of type 2 diabetes.
GDM is the most common metabolic alteration in pregnancy that, if not correctly recognized and adequately treated, is associated with high maternal–fetal morbidity, mainly related to excessive fetal growth (macrosomia). Numerous studies have shown that early treatment of GDM reduces the incidence of adverse pregnancy outcomes.
GDM is, from a biochemical point of view, characterized by reduced insulin secretion accompanied by increased peripheral insulin resistance, two conditions typical of type 2 diabetes mellitus. In GDM, reduced insulin secretion cannot compensate for the insulin resistance characteristic of pregnancy. Indeed, as already mentioned, during pregnancy, the organism undergoes a physiological adaptation characterized by endocrine-metabolic alterations necessary to guaran tee the supply of nutrients to the fetus and adequately prepare the maternal organism for childbirth and lactation (Table 1). These alterations are due to the action of hormones produced during pregnancy, such as estrogen, progesterone, cortisol, and placental lactogenic hormone.
Table1. Metabolic changes in pregnancy
The condition of insulin resistance that sets in with the progress of pregnancy, more evident in muscle and adipose tissue, is a physiological condition aimed at fetal growth. The reduced insulin-mediated utilization of glucose by the maternal organism determines, indeed, greater utilization of lipid substrates for energy purposes and, at the same time, guarantees the fetus a greater intake of carbohydrates. In addition, moderate but more prolonged postprandial hyperglycemia, which develops due to lower insulin sensitivity, favors the flow of nutrients from the mother to the fetus.
In GDM, the reduced action of insulin leads to an excess of nutrients in the circulation, such as glucose, lipids, and amino acids, which, crossing the placenta, cause hyperinsulinism in the fetus that, in turn, leads to organomegaly and macrosomia.
It is important to distinguish between overt diabetes in pregnancy and gestational diabetes. Manifest diabetes means the presence of diabetes that existed before pregnancy and was not recognized up to that moment; gestational diabetes means, instead, a form of diabetes that arose during pregnancy. The laboratory tests for diagnosing diabetes in pregnancy, both manifest diabetes and GDM, are fasting blood glucose, glycated hemoglobin, and the OGTT (oral glucose tolerance test). In particular, after pregnancy assessment, all women should be screened for overt diabetes by evaluating glycemia (fasting and random) and glycated hemoglobin within the first trimester of pregnancy. For the diagnosis of overt diabetes, the same criteria used in the general population are used:
• Fasting blood glucose ≥126 mg/dL (to be confirmed by a second blood test)
• Random blood glucose ≥200 mg/dL (to be confirmed by fasting blood glucose ≥126 mg/dL)
• HbA1c ≥ 48 mmol/mol (≥ 6.5%) (to be confirmed in a second sample)
Women diagnosed with overt diabetes should undergo intensive metabolic monitoring, as recommended for gestational diabetes.
Screening for GDM is based, first of all, on the assessment of specific risk factors (Table 2); women who present at least one risk factor for GDM should perform an OGTT with 75 g of glucose between the 24th and 28th weeks of pregnancy because GDM usually occurs in the second half of pregnancy. However, women with high risk factors should be screened early by performing a 75-g glucose OGTT between 16 and 18 weeks of pregnancy, to be repeated between 24 and 28 weeks if negative. Figure 1 shows the diagnostic procedure for screening and diagnosing diabetes in pregnancy.
Table2. Risk factors for gestational diabetes mellitus
Fig1. Gestational diabetes diagnostic algorithm. (Copyright EDISES 2021. Reproduced with permission)
Women with previous GDM should be screened for diabetes mellitus 2 by performing an OGTT with 75 g of glucose 6 weeks after delivery and within 6 months. If the test is negative, the OGTT should be repeated every 3 years; if impaired glucose tolerance (IFG or IGT) is found, the test should be repeated yearly.
The OGTT should be performed on an empty stomach in the morning by administering a solution consisting of 75 g of glucose dissolved in 300 mL of water. There are no particular indications to follow in the days preceding the test, but con suming at least 150 g of carbohydrates per day is recommended. During the test, assuming the sitting position and refrain from eating, drinking, and smoking is necessary. Blood sampling to obtain the plasma on which the glycemia will be performed by the enzymatic method will be done before the administration of the glucose solution (basal glycemia) and after 1 and 2 h from the administration of the solution. Table 3 shows the glycemia values that allow the diagnosis of gestational diabetes.
Table3. Diagnostic criteria for gestational diabetes mellitus
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