Diabetic Embryopathy

Etiology

The etiology of gestational diabetes mellitus is complex with environmental-genetic interaction. A major teratogen is hyperglycemia, followed by other by-products, including ketones, triglycerides, and branched-chain amino acids.[3] Lactate, pyruvate, and glycerol also have a minor role in teratogenicity. Hyperglycemia-induced oxidative stress and altered signaling mechanisms of arachidonic acids, prostaglandins, inositol, and other metabolic alterations result in placental abnormalities and hypoxia, which play a vital role in dysmorphogenesis. Of note, it has been found that despite hyperglycemia, glucose transporter 1 (GLUT1) is not downregulated in fetuses during neurulation, which is responsible for increased intracellular glucose. The embryo neural tissue at day 11-12 takes up glucose in equal concentration as the mother's serum potentially resulting in critical neural birth defects seen in infants born to poorly controlled diabetic mothers.

Epidemiology

Some ethnic or racial groups such as Hispanic, African, Southeast Asian, Native Americans have a higher prevalence of diabetes.[4] The prevalence of diabetes is rising in developed countries in the context of the global obesity epidemic. The frequency of pregnancies with type 2 diabetes is rising. The prevalence rate of pregestational type 1 and type 2 diabetes is 1.8%, and gestational diabetes is 7.5%. The rate of fetal anomalies is around 5 to 6% of gestational diabetes. This translates to a high burden risk of diabetic embryopathy in this particular population, and clinician suspicion is paramount.

Pathophysiology

The increased glucose level in the fetus is teratogenic and is the major cause of diabetic embryopathy. Further deterioration of normal physiology and organogenesis starts with hyperglycemia through multiple factors that are involved in this pathogenesis.[2]

Hyperglycemia and Ketone Bodies

Several experimental studies in mouse models show a direct correlation of hyperglycemia with congenital malformations. Increased glucose uptake by embryogenic tissue is teratogenic. Increased glucose flux enhances many other pathways, likely glycolytic flux, mitochondrial oxidative phosphorylation, and citric acid cycle. Sorbital accumulation from high glucose reduction by aldose reductase damages the cells through osmotic effect (however, it is not the key mechanism of diabetic embryopathy because the use of aldose reductase inhibitors does not show improvement in dysmorphogenesis in the presence of high glucose). Hyperglycemic stimulated AMP-kinase has found to induce the increased formation of Neural tube defects in in-vitro experiments of mice. Ketone bodies such as beta-hydroxybutyrate and acetoacetate are formed in increased amounts in the liver in the hyperglycemic state of the mother that crosses the placenta and also exerts teratogenic effects in the fetus. Synergistic evidence between hyperglycemia and other metabolites like ketones has been established. Hexosamine pathway activation in the hyperglycemic state deteriorates the antioxidant defense system and causes birth defects. Uridine-diphosphate N-acetyl glucosamine formation in this pathway is attached to the serine or threonine residues of proteins causing beta-o-linked glycosylation leading to hexosamine stress that is responsible for teratogenic effects.[5] Decreased Bcl-2 expression and increased Bax and caspase-3 expression in the hyperglycemic state enhance apoptosis. A new apoptotic pathway has been suggested to be activated by hyperglycemia.

Oxidative Stress

Diabetes-induced alterations of signaling systems lead to an imbalance between reactive oxygen species (ROS) production and stress defense system. Glucose autooxidation and mitochondrial production of superoxides, as well as unpaired electrons transfer from the mitochondrial electron chain transport system, are responsible for increased reactive oxygen species. Embryonic neural tissue has increased uptake of glucose for the proliferation of tissues. In a hyperglycemic environment, there is a further increase in the uptake of glucose by neural tissue. NADPH utilized in the polyol pathway further decreases GSH (glutathione reductase). GSH is required for DNA and protein synthesis. Gammaglutamilcysteine enzyme involved in GSH production is inhibited by excess glucose. So, the ability to reduce and neutralize the reactive species is decreased that further exacerbates the oxidative stress. Cell membrane integrity is weakened due to oxidative stress. ROS can damage all the components, including cell membranes, DNA, RNA, lipids peroxidation, and proteins. Increased intracellular ROS inhibits the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a rate-limiting enzyme, which then increases the sensitivity to ROS.[1] Ultimately, oxidative stress leads to apoptosis of fetal tissue. Oxidative stress-induced iNOS expression leads to nitrosative stress and apoptosis. Defects in autophagy of unfolded proteins and damaged cellular organelles have been demonstrated in the diabetic environment and are responsible for Endoplasmic reticulum stress (ER stress) in the neuroepithelium resulting in NTDs.[6] Autophagy is needed for neurulation and neural fold closure. One study endorsed that increased activity of transcription factor called Forkhead box O3 (foxO3) in diabetic patients is responsible for inhibition of autophagy. The deletion of the FOXO3a gene has demonstrated the restoration of autophagy that ameliorates neural tube defects.[7] ER stress also inhibits endocardial cell migration leading to heart defects, including atrioventricular septal defects.[8]

Hypoxic Stress

Before the development of blood vessels, increased O2 consumption by excess glucose metabolism exacerbates the hypoxic state by favoring the mitochondrial superoxide formation. In many studies, a decrease in oxygen level has shown an increased NTD rate.[1]

Inositol

Inositol uptake is decreased by fetal tissue in a hyperglycemic environment. Supplementation of inositol has shown a reduction in dysmorphogenesis and thus, possibly is an important mechanism of diabetic embryopathy. Additionally, a decreased level of phosphoinositol 2 (PIP2), PIP3, and diacylglycerol (DAG) are noted. PIP2 is a precursor of phospholipids, including phospholipase A2 in the embryo. Decreased phospholipase A2 causes the reduced formation of Arachidonic acid.

Arachidonic Acid and Prostaglandins

High glucose level inhibits cyclooxygenase (COX) enzymes. This enzyme is required for the production of prostaglandins in the fetus. Prostaglandins are vital for cellular life. Arachidonic acid is engaged in signaling as a second messenger. Prostaglandin E2 producing pathway plays a crucial role in neurulation. Isoprostane formation by peroxidation of arachidonic acid further decreases the arachidonic acid. This, in turn, results in an increased incidence of NTDs. 

Placental Alterations

Normal placental functioning and structure are imperative for fetal growth and development. Gestational diabetes changes the placental structures and vascular patterns. Higher placental growth factors in the diabetic environment result in neovascularization and thickening of the basal trophoblast membrane. Vascular disorganization, endothelial proliferation, decreased villous space causes fetal vasculitis and hypoxia. Additionally, modification of fibronectin and b laminin expression prevents cellular adhesion.[2]

Genetic Alterations

There are polymorphic genes that are responsible for susceptibility to fetal malformations in diabetic mothers, but the exact genetic cause remains unidentified. Advanced glycosylation products damage the DNA, which then exerts teratogenic effects. Oxidative stress alters the expression of genes encoding the free radical inhibiting enzymes such as superoxide dismutase and catalases. PAX3 is expressed in the neuroepithelium and is essential for the closure of the neural tube and inhibits P53-mediated apoptosis. High glucose concentration leads to inhibition of the PAX3 gene that, in turn, is involved in the incidence of neural tube defects (NTDs).[2] Glycosylation of histone proteins causes DNA instability. In addition, crosslinking of histone amino acid by glucose-6-phosphate and ADP ribose also contributes to DNA instability. The defect in TGF-beta has been involved in cardiac malformations. Hyperglycemia induces epigenetic changes such as aberrant DNA methylation and promoter of NF-kB that also has a teratogenic contribution.[7][9]

Histopathology

Diabetes causes histopathological changes in the uterus. Villous and placental vascular malformations are characteristics of the diabetic placenta. Distal villous maldevelopment is the pathological change in the placenta of diabetic women that can be appreciated on histopathological analysis. Dysmorphic villi, villous hypoplasia, and immaturity, abnormal abundant blood vessels in villi are common placental microscopic findings. Fetal vasculitis is another common finding that may be a marker of inflammatory response.[10] Sclerosis of glomerular mesangium and formation of Kimmelstiel-Wilson nodules, as well as hyaline arteriosclerosis in kidney biopsy, support the diabetic pathology in these pregnancies.

History and Physical

A thorough history of the patient and his/her mother is paramount. Maternal history of past medical conditions, medications, history of abnormal glucose tolerance, or previous adverse pregnancy complications, as well as family history, including that of first-degree relatives with diabetes, is important. Poorly controlled gestational diabetes can also manifest with fetal malformations and complications. It is important to note that there may be other confounders resulting in congenital anomalies, including advanced maternal age, a specific race, or ethnic group, as previously mentioned, and body mass index of more than 25 are high-risk cases for the development of gestational diabetes.[4]

Physical examination of the child at birth is important to assess for birth defects. These infants are also at risk for hypoglycemia and complicated delivery course. Common birth defects identified include neural tube defects, craniofacial defects such as cleft palate, hydrocephaly, microcephaly, micrognathia, anencephaly. Ear and ocular abnormalities include microphthalmia and lens opacity, among other findings. Heart defects are also fairly common in this population, which includes the tetralogy of Fallot or a ventricular septal defect. Spina bifida is a distinct and common finding in these infants.

Evaluation

Clinicians must have a high index of suspicion for diabetes during pregnancy and screen offsprings of women in high-risk populations.[4]

Monitoring of Glucose Level

1-hr glucose challenge test with 50 gm of glucose at 24-28wks of gestation. More than 130-140 gm/dl serum glucose level one hour after oral intake is abnormal. Those women who fail to respond to 1-hr screening should be provided with a 3-hr glucose tolerance test. More aggressive testing is vigilant in high-risk groups. Testing of hemoglobin A1c before conception helps to identify high-risk populations.

Ultrasound and Growth Monitoring

Ultrasound is the principal imaging modality for fetal monitoring and the status of pregnancy. Viability is checked in the first trimester, whereas structural integrity is monitored in the second trimester. The gestational sac can be visualized as early as 4-5 weeks of gestation and the yolk sac at about five weeks to check the viability of early pregnancy. Embryos can be measured at 5-6 weeks of gestation. Fetal growth and wellbeing are monitored during the third trimester. The biophysical profile provides information regarding the wellbeing and risk for potential asphyxia. Diagnosis of fetal abnormality with ultrasound is best around or before 20 weeks of gestation. Detection rates vary according to the type of fetal anomaly.[11]

Doppler Ultrasound and Cardiotocograph

Fetal and placental vascularity can be assessed by doppler ultrasound. Fetal vasculitis and villous abnormalities can be detected by doppler.[10] A fetal echocardiogram can detect fetal heart sounds and abnormalities. 

Fetal MRI

This can be considered in the case of an ultrasound suspect of multiple congenital anomalies or technical limitations due to issues such as obesity and/or excess or reduced amniotic fluid.

Fetal Alpha-fetoprotein

This should be tested during 16-18 weeks. A high level of alpha-fetoprotein in maternal serum indicates risk for neural tube defects, among other causes.

Fetal Lung Maturity

Fetal lung maturity is assessed after 32 weeks of gestation. Phosphatidylglycerol levels can be evaluated through amniotic fluid analysis. The lecithin/sphingomyelin ratio is also crucial.

Additional monitoring includes non-stress tests twice a week after 32 weeks, and contraction stress tests if there is a failed nonstress test.

Treatment / Management

Preconceptional surveillance of high-risk populations can reduce the incidence of fetal malformations. Tight glycemic control and the use of supplementary diets before conception is the best way of prevention and management.[12][13] Reducing and maintaining HBA1c below 6.1% and having a goal of body mass index of less than 25 during the preconception period should be advised to all women. Several studies have demonstrated the benefits of folic acid supplementation(5mg/day) starting even prior to conception reduces the incidence of neural tube defects.[14](B3)

High-risk populations with high hemoglobin A1c levels should be counseled before conception with the goal to achieve normal glucose homeostasis before pregnancy. This could potentially prevent structural birth defects because organogenesis starts early in pregnancy, often even prior to women knowing that she is pregnant.

Nutritional interventions and monitoring of normal blood glucose levels should be the primary therapeutic goal. Change of lifestyle, dietary interventions, and daily light exercise is recommended. Exercise can have an overall positive impact on health by reducing both fasting and postprandial hyperglycemia and overcoming insulin resistance by reducing the number of adipocytes. Reducing carbohydrate use and maintaining normal sugar levels are helpful in the prevention of ketosis and hyperglycemia. Quantity of calorie intake is a challenging part. Many studies recommended that 30 kilocalories (kcal) per kilogram (kg) body weight for women of normal body mass index, 24 kcal/kg body weight for overweight women, and only 12-15 kcal/kg for obese women should be considered. Food distributions should be done according to carbohydrate content. Some carbohydrate-containing foods based upon the ability to increase the blood sugar level should be monitored because some foods with the same carbohydrate content have disparate effects on blood sugar levels. Diets having a low glycemic index also reduces the chance of macrosomia. Low-glycemic and high fiber diets decrease the need for insulin.[15] Multiple human and animal studies have also demonstrated the positive role of vitamin D in insulin sensitivity and insulin secretion.

Inositols: It has been clear that hyperglycemia has negative effects on inositol regulation and functioning. Dietary supplementation of inositol-rich nutrients such as cereals, maize, legumes, and meat has shown some improvement in fetal organogenesis and growth.[16] Administration of inositol isomers (myoinositol or D-chiro-inositol) formulation has been known to be beneficial for gestational diabetes.[17](A1)

Fish oil: Fish oil is rich in omega-3, which is a source of eicosapentaenoic acid and docosahexaenoic acid that upregulates the peroxisome-proliferator activated receptor-gamma gene expression and enhances the adiponectin gene expression.[18][19] Omega-3 supplementation reduces the inflammatory cytokine release by inhibiting the activation of NF-kB.[20](B3)

Drug therapy: Insulin is administered to gestational diabetic women only after failure of primary nutritional intervention because drugs should be avoided as much as possible to preclude adverse effects on fetuses. Some studies have revealed that a mother treated with insulin has fewer chances of anomalies than those without insulin therapy even after having the same glucose level. The use of oral metformin is acceptable given oral formulation and is considered safe for the treatment of gestational diabetes.[15] Administration of antioxidants such as ascorbic acid, Vitamin E, and beta carotene are theoretically said to help prevent malformations by counteracting oxidative stress.[2](B3)

Surveillance of the fetus during the first trimester can be done with ultrasound, and further imaging, including MRI and fetal echocardiogram, can be done to better delineate anomalies if present. Specific knowledge of the plan for delivery, expected complications, and psychological support for the mother should be considered during follow-up visits. 

Differential Diagnosis

The various structural anomalies of diabetic embryopathy resemble other various types of syndromes having similar defects.

Neural Tube Defects (NTDs)

NTDs are birth defects due to failure neural tube formation caused by several factors besides gestational or pre-existing diabetes in the mother. Folic acid deficiency is the major cause of NTDs. Other causes of NTDs include Vit B 12 deficiency and many other genetic syndromes.

DiGeorge Syndrome

The clinical presentation and structural defects can resemble that of diabetic embryopathy. Cardiac anomalies, facial dysmorphism, and impaired learning abilities mimic that of diabetic embryopathy complications.[21]

VACTERL

It consists of vertebral anomalies, anal atresia, cardiac defect, tracheoesophageal fistula, renal abnormalities, and/or limb abnormalities. Maternal prenatal history of diabetes can help differentiate this condition from diabetic embryopathy.[22]

CHARGE Syndrome

This disorder affects many organ systems of the body. It consists of coloboma, heart defects, atresia choanae (also known as choanal atresia), growth retardation, genital abnormalities, and ear abnormalities.[23]

Prognosis

Pregnancy outcomes are affected by maternal diet during pregnancy. Preconceptional evaluation of maternal risk factors and blood glucose levels helps in prognostication. Strict glycemic control is the best way to prevent and/or reduce the incidence of congenital anomalies.[12]

The perinatal mortality rate of a diabetic pregnancy is 2.5-9 times higher than the general population. Several studies have demonstrated that type 2 diabetes is associated with a higher rate of perinatal deaths than type 1 diabetes due to more associated risk factors such as hypertension, older age, obesity, multiparity, etc however French studies revealed that stillbirths are more common in type 1 diabetes.

Complications

Diabetic women with higher than normal HBA1c levels have around 22% chance of fetal complications. High glucose levels after 32 weeks of gestation have been associated with macrosomia, polycythemia, and hypoglycemia. Major complications of diabetic embryopathy are congenital malformations. The central nervous system and cardiovascular systems are mainly affected, but any organ can be affected. Around 8-12% of all diabetic pregnancies have been associated with malformations.

Central Nervous System

These are comprised of neural tube defects, hydrocephalus, anencephaly with or without herniated neural elements, holoprosencephaly, microcephaly, caudal dysgenesis, hydranencephaly, and many others.[2] Mental retardation and cognitive impairment are possible long-term sequelae. 

Cardiovascular System

Transposition of large vessels with or without ventricular septum defects is the most common defect found in infants of diabetic mothers. Hypoplasia of the left heart, atrial and ventricular septum defects, hypertrophy cardiomyopathy, coarctation of the aorta, tetralogy of Fallot are some of the other heart defects.

Perinatal Mortality of the Child

Perinatal deaths in gestational diabetes are higher than in the background population. Stillbirths that are increased in diabetic mothers consist of 44 to 84% of all the perinatal mortality rates.[24] Many women may opt for the abortion of a child with multiple malformations. Modern methods of early diagnosis and management have reduced perinatal mortality.[25] Prematurity and preterm delivery are also reported in these cases, which increases the risk of complications in the neonatal period. 

Other Malformations

This includes birth defects involving many other organ systems. The oculoauriculovertebral spectrum is one of the rare disorders due to defective organogenesis. It is a craniofacial disorder with associated vertebral column abnormality. Ear structure abnormality, along with hearing loss is the most common manifestation followed by hemifacial microsomia, ocular anomalies, and vertebral column anomalies. Other findings include femoral hypoplasia, renal agenesis, growth delays, and macrosomia at birth. 

Long-term Complications in Offspring

Children born from diabetic mothers have chances of increased incidence of metabolic syndrome, diabetes, and insulin resistance later on in life. Shoulder dystocia is common in a macrosomic child during delivery. Later in life, polycythemia due to fetal hypoxia stimulated erythropoietin production, and subsequent hyperbilirubinemia is evident. Other electrolyte deficiencies such as hypocalcemia, hypomagnesia are less common. Respiratory distress due to decreased surfactant levels in premature child and hypoglycemia due to maternal hyperinsulinemia has also been reported in some cases.[4][26]