Genetic and Epigenetic Mechanisms of Developing Gestational Diabetes Mellitus and Its Effects on the Fetus

The study aims to clarify the effect of hyperglycemia and its correction, the level of physical activity and consumption of major macro- and micronutrients by women during pregnancy on DNA methylation and expression of genes involved in neuroendocrine regulation and development of metabolic diseases in offspring, as well as functional characteristics of human umbilical vein endothelial cells (HUVECs). For the purpose of the study women with GDM are randomised to 2 treatment groups per glycemic targets ( very tight and tight-moderate glycemic targets). Data on glycenmic levels during the study and consumption of major macro- and micronutrients will be collected using a mobile application with electronic dairies report forms. This clinical trial record primarily describes the overarching observational cohort study "Genetic and Epigenetic Mechanisms of Developing Gestational Diabetes Mellitus and Its Effects on the Fetus" including women with GDM and healthy pregnant women. Substudy Protocol: A key predefined component of this larger study is an interventional, randomized controlled substudy entitled "Tight versus less tight glycaemic targets for women with gestational diabetes mellitus: a randomised controlled trial" (also known as the GEM GDM Trial). The GEM GDM Trial is an open-label, randomized controlled trial (RCT) that compares the effects of tight (very tight) versus less tight (tight-moderate) glycemic control on maternal and neonatal outcomes in women diagnosed with Gestational Diabetes Mellitus (GDM). Participants from the main GEM cohort who are diagnosed with GDM according to International Association of the Diabetes and Pregnancy Study Groups (IADPSG) criteria are eligible for screening and subsequent randomization into this substudy. The substudy aims to enroll 650 pregnant women with a singleton pregnancy and GDM, randomly assigning them in a 1:1 ratio to one of two glycemic target groups. * Tight Target Group: Fasting capillary glucose \<5.1 mmol/L (\<92 mg/dL); 1-hour postprandial glucose \<7.0 mmol/L (\<126 mg/dL). * Less Tight Target Group: Fasting capillary glucose \<5.3 mmol/L (\<95 mg/dL); 1-hour postprandial glucose \<7.8 mmol/L (\<140 mg/dL).