[Clinical practice recommendations for diabetes in pregnancy (Update 2023)]

In 1989 the St. Vincent Declaration aimed to achieve comparable pregnancy outcomes in women with diabetes and those with normal glucose tolerance. However, currently women with pre-gestational diabetes still feature a higher risk of perinatal morbidity and even increased mortality. This fact is mostly ascribed to a persistently low rate of pregnancy planning and pre-pregnancy care with optimization of metabolic control prior to conception. All women should be experienced in the management of their therapy and on stable glycemic control prior to conception. In addition, thyroid dysfunction, hypertension as well as the presence of diabetic complications should be excluded or treated adequately before pregnancy in order to decrease the risk for a progression of complications during pregnancy as well as maternal and fetal morbidity. Near normoglycaemia and HbA_1c in the normal range are targets for treatment, preferably without the induction of frequent resp. severe hypoglycaemic reactions. Especially in women with type 1 diabetes mellitus the risk of hypoglycemia is high in early pregnancy, but it decreases with the progression of pregnancy due to hormonal changes causing an increase of insulin resistance. In addition, obesity increases worldwide and contributes to higher numbers of women at childbearing age with type 2 diabetes mellitus and adverse pregnancy outcomes. Intensified insulin therapy with multiple daily insulin injections and pump treatment are equally effective in reaching good metabolic control during pregnancy. Insulin is the primary treatment option. Continuous glucose monitoring often adds to achieve targets. Oral glucose lowering drugs (Metformin) may be considered in obese women with type 2 diabetes mellitus to increase insulin sensitivity but need to be prescribed cautiously due to crossing the placenta and lack of long-time follow up data of the offspring (shared decision making). Due to increased risk for preeclampsia in women with diabetes screening needs to be performed. Regular obstetric care as well as an interdisciplinary treatment approach are necessary to improve metabolic control and ensure the healthy development of the offspring.

Mechanisms of Congenital Malformations in Pregnancies with Pre-existing Diabetes

PURPOSE OF REVIEW

Fetuses of diabetic mothers are at increased risk for congenital malformations. Research in recent decades using animal and embryonic stem cell models has revealed many embryonic developmental processes that are disturbed by maternal diabetes. The aim of this review is to give clinicians a better understanding of the reasons for rigorous glycemic control in early pregnancy, and to provide background to guide future research.

RECENT FINDINGS

Mouse models of diabetic pregnancy have revealed mechanisms for altered expression of tissue-specific genes that lead to malformations that are more common in diabetic pregnancies, such as neural tube defects (NTDs) and congenital heart defects (CHDs), and how altered gene expression causes apoptosis that leads to malformations. Embryos express the glucose transporter, GLUT2, which confers susceptibility to malformation, due to high rates of glucose uptake during maternal hyperglycemia and subsequent oxidative stress; however, the teleological function of GLUT2 for mammalian embryos may be to transport the amino sugar glucosamine (GlcN) from maternal circulation to be used as substrate for glycosylation reactions and to promote embryo cell growth. Malformations in diabetic pregnancy may be not only due to excess glucose uptake but also due to insufficient GlcN uptake. Avoiding maternal hyperglycemia during early pregnancy should prevent excess glucose uptake via GLUT2 into embryo cells, and also permit sufficient GLUT2-mediated GlcN uptake.

Disturbed intracellular calcium homeostasis in neural tube defects in diabetic embryopathy

Pregnancies complicated by preexisting maternal diabetes mellitus are associated with a higher risk of birth defects in infants, known as diabetic embryopathy. The common defects seen in the central nervous system result from failure of neural tube closure. The formation of neural tube defects (NTDs) is associated with excessive programmed cell death (apoptosis) in the neuroepithelium under hyperglycemia-induced intracellular stress conditions. The early cellular response to hyperglycemia remains to be identified. We hypothesize that hyperglycemia may disturb intracellular calcium (Ca²⁺) homeostasis, which perturbs organelle function and apoptotic regulation, resulting in increased apoptosis and embryonic NTDs. In an animal model of diabetic embryopathy, we performed Ca²⁺ imaging and observed significant increases in intracellular Ca²⁺ ([Ca²⁺]_i) in the embryonic neural epithelium. Blocking T-type Ca²⁺ channels with mibefradil, but not L-type with verapamil, significantly blunted the increases in [Ca²⁺]_i, implicating an involvement of channel type-dependent Ca²⁺ influx in hyperglycemia-perturbed Ca²⁺ homeostasis. Treatment of diabetic pregnant mice with mibefradil during neurulation significantly reduced NTD rates in the embryos. This effect was associated with decreases in apoptosis, alleviation of endoplasmic reticulum stress, and increases of anti-apoptotic factors. Taken together, our data suggest an important role of Ca²⁺ influx in hyperglycemia-induced NTDs and of T-type Ca²⁺ channels as a potential target to prevent birth defects in diabetic pregnancies.

Maternal diabetes and high glucose in vitro trigger Sca1+ cardiac progenitor cell apoptosis through FoxO3a

Recent controversies surrounding the authenticity of c-kit⁺ cardiac progenitor cells significantly push back the advance in regenerative therapies for cardiovascular diseases. There is an urgent need for research in characterizing alternative types of cardiac progenitor cells. Towards this goal, in the present study, we determined the effect of maternal diabetes on Sca1⁺ cardiac progenitor cells. Maternal diabetes induced caspase 3-dependent apoptosis in Sca1⁺ cardiac progenitor cells derived from embryonic day 17.5 (E17.5). Similarly, high glucose in vitro but not the glucose osmotic control mannitol triggered Sca1⁺ cardiac progenitor cell apoptosis in a dose- and time-dependent manner. Both maternal diabetes and high glucose in vitro activated the pro-apoptotic transcription factor, Forkhead O 3a (FoxO3a) via dephosphorylation at threonine 32 (Thr-32) residue. foxo3a gene deletion abolished maternal diabetes-induced Sca1⁺ cardiac progenitor cell apoptosis. The dominant negative FoxO3a mutant without the transactivation domain from the C terminus blocked high glucose-induced Sca1⁺ cardiac progenitor cell apoptosis, whereas the constitutively active FoxO3a mutant with the three phosphorylation sites, Thr-32, Ser-253, and Ser-315, being replaced by alanine residues mimicked the pro-apoptotic effect of high glucose. Thus, maternal diabetes and high glucose in vitro may limit the regenerative potential of Sca1⁺ cardiac progenitor cells by inducing apoptosis through FoxO3a activation. These findings will serve as the guide in optimizing the autologous therapy using Sca1⁺ cardiac progenitor cells in cardiac defect babies born exposed to maternal diabetes.

microRNA expression profiling and functional annotation analysis of their targets modulated by oxidative stress during embryonic heart development in diabetic mice

Maternal pregestational diabetes mellitus (PGDM) induces congenital heart defects (CHDs). The molecular mechanism underlying PGDM-induced CHDs is unknown. microRNAs (miRNAs), small non-coding RNAs, repress gene expression at the posttranscriptional level and play important roles in heart development. We performed a global miRNA profiling study to assist in revealing potential miRNAs modulated by PGDM and possible developmental pathways regulated by miRNAs during heart development. A total of 149 mapped miRNAs in the developing heart were significantly altered by PGDM. Bioinformatics analysis showed that the majority of the 2111 potential miRNA target genes were associated with cardiac development-related pathways including STAT3 and IGF-1 and transcription factors (Cited2, Zeb2, Mef2c, Smad4 and Ets1). Overexpression of the antioxidant enzyme, superoxide dismutase 1, reversed PGDM-altered miRNAs, suggesting that oxidative stress is responsible for dysregulation of miRNAs. Thus, our study provides the foundation for further investigation of a miRNA-dependent mechanism underlying PGDM-induced CHDs.

Reevaluation of Antioxidative Strategies for Birth Defect Prevention in Diabetic Pregnancies

Diabetes mellitus in early pregnancy is the most severe maternal disease that is counted for 10% of newborn infants with structural defects. With the rapid increases in the number of diabetic women in childbearing age, the birth defect rate is projected to elevate dramatically. Thus, prevention of embryonic malformations becomes an urgent task. Animal studies have revealed an involvement of oxidative stress in diabetic embryopathy and treatment with antioxidants can reduce embryonic abnormalities. However, the failure of clinical trials using free radical-scavenging antioxidants to alleviate oxidative stress-related diseases prompts researchers to reevaluate the strategy in birth defect prevention. Hyperglycemia also disturbs other intracellular homeostasis, generating aberrant conditions. Perturbed folding of newly synthesized proteins causes accumulation of unfolded and misfolded proteins in the lumen of the endoplasmic reticulum (ER). The ER under the stress activates signaling cascades, known as unfolded protein response, to suppress cell mitosis and/or trigger apoptosis. ER stress can be ameliorated by chemical chaperones, which promote protein folding. Hyperglycemia also stimulates the expression of nitric oxide (NO) synthase 2 (NOS2) to produce high levels of NO and reactive nitrogen species and augment protein nitrosylation and nitration, resulting in nitrosative stress. Inhibition of NOS2 using inhibitors has been demonstrated to reduce embryonic malformations in diabetic animals. Therefore, targeting ER and nitrosative stress conditions using specific agents to prevent birth defects in diabetic pregnancies warrant further investigations. Simultaneously targeting multiple stress conditions using combined agents is a potentially effective and feasible approach.

[Clinical practice recommendations for diabetes in pregnancy (Diabetes and Pregnancy Study Group of the Austrian Diabetes Association)]

Twenty-six years ago the St. Vincent Declaration aimed for an achievement of a comparable pregnancy outcome in diabetic and non-diabetic women. However, current surveys clearly show that women with pre-gestational diabetes still feature a much higher risk of perinatal morbidity and even increased mortality. This fact is mostly ascribed to a persistently low rate of pregnancy planning and pre-pregnancy care with optimization of metabolic control prior to conception. In addition, obesity increases worldwide, contributing to a growing number of women with type 2 diabetes at a childbearing age, and a further deterioration in outcome in diabetic women. Development of diabetic embryopathy and fetopathy are known to be related to maternal glycemic control (target: normoglycemia and normal HbA1c, if possible without hypoglycemia). The risk for hypoglycemia is at its greatest in early pregnancy and decreases with the progression of pregnancy due to the hormonal changes leading to a marked increase of insulin resistance. Intensified insulin therapy with multiple daily insulin injections and pump treatment are equally effective in reaching good metabolic control during pregnancy. All women should be experienced in the management of their therapy and on stable glycemic control prior to the conception. In addition, thyroid dysfunction, hypertension as well as the presence of diabetic complications should be excluded before pregnancy or treated adequately in order to decrease the risk for a progression of complications during pregnancy as well as for maternal and fetal morbidity.

Identification of novel cell survival regulation in diabetic embryopathy via phospholipidomic profiling

Diabetes mellitus in early pregnancy causes birth defects by disturbing metabolic homeostasis and increasing programmed cell death in the embryo. Over-activation of phospholipase Cβ3 and γ1 suggests disturbed phospholipid metabolism, which is an important in regulation of cell signaling and activity. Metabolomic examinations reveal significant changes in the profile of phospholipid metabolism. Among the metabolites, levels of phosphatidylinositol bisphosphate (PIP2) are increased. PIP2 effector PTEN (phosphatase and tensin homolog deleted on chromosome 10) is activated. Activation of protein kinase Bα (PKBα, or AKT1) and mTOR (mechanistic target of rapamycin) is decreased. Inhibition of PLCs and PTEN suppresses over-generation of reactive oxygen species and inhibition of PLCs prevents fragmentation of mitochondria in neural stem cells cultured in high glucose. These observations suggest that maternal hyperglycemia disrupts phospholipid metabolism, leading to perturbation of mitochondrial dynamics and redox homeostasis and suppression of the PKB-mTOR cell survival signaling in the embryos.

Maternal diabetes triggers DNA damage and DNA damage response in neurulation stage embryos through oxidative stress

DNA damage and DNA damage response (DDR) in neurulation stage embryos under maternal diabetes conditions are not well understood. The purpose of this study was to investigate whether maternal diabetes and high glucose in vitro induce DNA damage and DDR in the developing embryo through oxidative stress. In vivo experiments were conducted by mating superoxide dismutase 1 (SOD1) transgenic male mice with wild-type (WT) female mice with or without diabetes. Embryonic day 8.75 (E8.75) embryos were tested for the DNA damage markers, phosphorylated histone H2A.X (p-H2A.X) and DDR signaling intermediates, including phosphorylated checkpoint 1 (p-Chk1), phosphorylated checkpoint 2 (p-Chk2), and p53. Levels of the same DNA damage markers and DDR signaling intermediates were also determined in the mouse C17.2 neural stem cell line. Maternal diabetes and high glucose in vitro significantly increased the levels of p-H2A.X. Levels of p-Chk1, p-Chk2, and p53, were elevated under both maternal diabetic and high glucose conditions. SOD1 overexpression blocked maternal diabetes-induced DNA damage and DDR in vivo. Tempol, a SOD1 mimetic, diminished high glucose-induced DNA damage and DDR in vitro. In conclusion, maternal diabetes and high glucose in vitro induce DNA damage and activates DDR through oxidative stress, which may contribute to the pathogenesis of diabetes-associated embryopathy.

Birth defects in pregestational diabetes: Defect range, glycemic threshold and pathogenesis

Currently, 60 million women of reproductive age (18-44 years old) worldwide, and approximately 3 million American women have diabetes mellitus, and it has been estimated that this number will double by 2030. Pregestational diabetes mellitus (PGD) is a significant public health problem that increases the risk for structural birth defects affecting both maternal and neonatal pregnancy outcome. The most common types of human structural birth defects associated with PGD are congenital heart defects and central nervous system defects. However, diabetes can induce birth defects in any other fetal organ. In general, the rate of birth defects increases linearly with the degree of maternal hyperglycemia, which is the major factor that mediates teratogenicity of PGD. Stringent prenatal care and glycemic control are effective means to reduce birth defects in PGD pregnancies, but cannot reduce the incidence of birth defects to the rate of that is seen in the nondiabetic population. Studies in animal models have revealed that PGD induces oxidative stress, which activates cellular stress signalling leading to dysregulation of gene expression and excess apoptosis in the target organs, including the neural tube and embryonic heart. Activation of the apoptosis signal-regulating kinase 1 (ASK1)-forkhead transcription factor 3a (FoxO3a)-caspase 8 pathway causes apoptosis in the developing neural tube leading to neural tube defects (NTDs). ASK1 activates the c-Jun-N-Terminal kinase 1/2 (JNK1/2), which leads to activation of the unfolded protein response and endoplasmic reticulum (ER) stress. Deletion of the ASK1 gene, the JNK1 gene, or the JNK2 gene, or inhibition of ER stress by 4-Phenylbutyric acid abrogates diabetes-induced apoptosis and reduces the formation of NTDs. Antioxidants, such as thioredoxin, which inhibits the ASK1-FoxO3a-caspase 8 pathway or ER stress inhibitors, may prevent PGD-induced birth defects.