Circulating microRNAs as modifiable diagnostic biomarkers of gestational and transgenerational metabolic risk: can exercise play a role?
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance at first recognition during pregnancy (1). It is usually diagnosed at 24–28 gestational weeks, according to the recommendations of international associations and committees (2). Diagnosis is made using a sequential model of universal screening with a 50-g one-hour glucose challenge test (GCT), followed by a diagnostic 100-g three-hour oral glucose tolerance test (OGTT) for women with a positive screening test (3). The overall incidence of GDM is increasing worldwide, affecting approximately 7–15% of all pregnancies (4). It is considered the most frequent metabolic problem during pregnancy, representing about 90% of risky pregnancies (5), although the prevalence of pregnancies complicated by diabetes (gestational or pre-gestational) varies geographically and among different ethnic groups (6). During healthy pregnancy insulin resistance increases due to the secretion of a series of placental hormones antagonists to insulin (cortisol, prolactin, progesterone and lactogen), ultimately causing blood glucose to rise (6). Furthermore, in GDM women insulin production is insufficient to counteract this increasing insulin resistance, due to an increase in β-pancreatic cells apoptotic rate which leads to an abnormal production and secretion of insulin (7). Given that blood glucose easily goes through placenta by facilitated diffusion, it reaches the fetus producing fetal hyperglycemia (8).