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Gestational DiabetesAuthor: Daniela Contage Siccardi, MD |
Gestational diabetes(GDM) is defined as glucose intolerance of variable degree with onset or first recognition during the present pregnancy. It can be screened by drawing a 1-hour glucose level following a 50-g glucose load, but is definitively diagnosed only by an abnormal 3-hour OGTT following a 100-g glucose load.
The growth and maturation of the fetus are closely associated with the delivery of maternal nutrients, particularly glucose. This is most crucial in the third trimester and is directly related to the duration and degree of maternal glucose elevation. Thus, the negative impact is as highly diverse as the variety of carbohydrate intolerance that women bring to pregnancy.
For the mother with GDM there is a higher risk of hypertension, preeclampsia, urinary tract infections, cesarean section, and future diabetes. Many of the problems associated with overt diabetic pregnancies can be seen in infants of gestational diabetic pregnancies, such as macrosomia, neural tube defects, neonatal hypoglycemia, hypocalcemia, hypomagnsemia, hyperbilirubinemia,birth trauma, prematurity syndromes, and subsequent childhood and adolescent obesity.
The prevalence of GDM varies worldwide and among different racial and ethnic groups within a country. The variability is partly because of the different criteria and screening regimens(i.e., not all pregnant women are screened). Studies using a 100-g 3-hour OGTT and either the criteria of the National Diabetes Data Group(NDDG) or of Carpenter and Coustan have found prevalence rates of 1.4% to 12.3% in the United States, respectively.
Gestational diabetes is pathophysiologically similar to type II diabetes. Approximately 90% of the persons identified have a deficiency of insulin receptors(prior to pregnancy) or a marked increase in weight that has been placed on the abdominal region. The other 10% have deficient insulin production and will proceed to develop mature-onset insulin-dependent diabetes.
HPL blocks insulin receptors and increases in direct linear relation to the length of pregnancy. Insulin release is enhanced in an attempt to maintain glucose homeostasis. The patient experiences increased hunger due to the excess insulin release as a result of elevated glucose levels. This insulin release further decreases insulin receptors due to elevated hormonal levels.
The traditional method of screening for GDM is to assess risk factors: age, prepregnancy weight, family history of diabetes in a first-degree relative, previous large baby, and previous perinatal loss. Unfortunately, screening based solely on risk factors will only identify approximately 50% of women with GDM.
The ADA(American Diabetes Association) recommend that all pregnant women, who have not been identified with glucose intolerance earlier in pregnancy, be screened with a 50-g 1-hour GCT between 24 and 28 weeks of pregnancy. Such test can be performed at anytime of the day and with disregard to previous meal ingestion. A value equal to or above 140mg/dL should be used as the threshold level and indicates the need for a 100-g 3-hour OGTT. For the OGTT, the patient is fasting and receives 100-g of glucose after a fasting glucose level is obtained. A blood sample is taken every hour for 3 hours. The patient is advised to sit quietly during the test to minimize the impact of exercise on glucose levels.
The glucose values used to detect gestational diabetes were first determined by O’Sullivan (1964) in a retrospective study designed to detect risk of developing type II diabetes in the future. The values were set using venous whole blood and required 2 values reaching or exceeding the value to be positive See Table 1. Subsequent information has led to alteration in O’Sullivan’s criteria. For example: when methods for blood glucose determination changed from the use of whole blood to venous plasma samples, the criteria for GDM were also changed once whole blood glucose values are lower than plasma levels due to glucose uptake by hemoglobin (NDDG,1979).
Since the adoption of the NDDG criteria, more specific glucose oxidase or hexokinase tests for glucose determination have replaced older methods, and new threshold values have been calculated by Carpenter and Coustan. Sacks and co-workers also have shown that correction of the O’Sullivan’s cutoffs may be necessary and suggested new cutoff values in 1989See Table 1.
If one abnormal value is seen during the 100-g 3-hour OGTT it is recommended that the test be repeated approximately 1 month later. There is growing evidence that 1 abnormal value is sufficient to make an impact on the health of the fetus and is now the criterion used by most clinicians to initiate treatment. In a study of 106 women with one abnormal value on the OGTT, 34% were diagnosed with GDM when the test was repeated 1 month later, emphasizing the importance of repeat testing when only one abnormal value is found.
OBS.: If GDM and fetal macrosomia begin to develop in the first trimester, then a diagnostic test to identify women at risk for GDM and to predict infants at risk for macrosomia should be accurate in the first trimester.
The reason for lowering the glucose level to a normoglycemic one is to prevent diabetic complications. The goal of medical management of women with GDM, therefore, is to prevent perinatal morbidity and mortality by normalizing the level of glycemia and other metabolites(i.e., lipids and amino acids) to the levels of nondiabetic pregnant individuals.
Dietary Therapy
Nutritional counseling is the mainstay of therapy for the gestational diabetic woman. The optimal dietary prescription would be one that provides the calories and nutrients necessary for maternal and fetal health, results in normoglycemia, prevents ketosis, and results in appropriate weight gain.
One of the difficulties with dietary prescription for women with GDM is the difference between lean and obese women. Obese women with GDM may benefit from a low calorie diet and weight reduction to reverse the metabolic disturbances, but proper nutrition is needed to assure fetal growth and development.
Jovanovic and Peterson found the following diet to result in euglycemia: 30kcal/kg/24h present pregnant weight for normal-weight women, 24kcal/kg/24h for overweight women (120%-150% ideal body weight ), 12 to 15 kcal/kg/24h for morbidly obese women ( >150% ideal body weight ), and 40kcal/kg/24h for underweight women( <80% ideal body weight ). They recommend that the diet be composed of 40% to 50% carbohydrate, 20% to 25% protein, and 30% to 40% fat ( polyunsaturated).
The patient checks her glucose 4 times daily (eg., fasting,and 1-hour postprandial breakfast, lunch, dinner ). The desired values are a fasting of <90mg/dL and a 1-hour <130mg/dL. The average glucose levels should be~90. After she has obtained a good understanding of her diet and the glucose values are in the desired range, she can decrease the frequency of testing to 3 days per week chosen randomly.
Insulin Therapy
If diet is not successful in maintaining relative euglycemia, then insulin therapy is recommended. To identify the women who will require insulin, circulating glucose levels should be monitored at frequent intervals. The ADA and ACOG( American College of Obstetricians and Gynecologists ) recommend glucose measurements be taken both fasting and after meals to 1 to 2-week intervals. Insulin therapy should be initiated if the fasting glucose levels exceed 105mg/dL and/or if the 2-hour postprandial levels exceed 120mg/dL on two or more occasions within a 2-week interval.
Several centers, however, use the 1-hour time point because it reflects the peak glycemic response to a meal. Two studies have found that the 1-hour postprandial glucose level was a better predictor of infant birth weight than the fasting level. For this reason, when the fasting blood glucose level is 90mg/dL or more, or the 1-hour postprandial glucose is 120mg/dL or more on two or more glucose measurements within 1 or 2 weeks, then insulin therapy is initiated. Several regimens are possible for insulin therapy. Jovanovic and Peterson suggest the regimen seen on Table 2 and Table 3.
Exercise Therapy
Cardiovascular conditioning or aerobic exercise has both acute and long-term effects on insulin sensitivity, insulin secretion, and glucose metabolism. Because exercise is associated with a decrease in blood glucose concentration both acutely and after a training program and exercise training with weight control or reduction is associated with lower fasting and postprandial insulin concentrations and apparent increases in insulin sensitivity, regular exercise may be useful in the treatment or prevention of GDM.
There are many other potential benefits of exercise training and increased cardiorespiratory fitness, such as improvement in cardiovascular risk factors and the prevention or reduction of cardiovascular complications in people with diabetes.
Recognizing the importance of physical activity, the Third International Workshop-Conference on Gestational Diabetes has recommended exercise as a treatment modality for GDM in women who do not have a medical or obstetric contraindication for an exercise program.
Antepartum Care
Surveillance for fetal well-being should begin between 28 and 32 weeks. Methods of fetal surveillance may include fetal kick counts, the nonstress test(NST), the contraction stress test (CST), and the biophysical profile. Signs of fetal compromise include the following: decreased fetal movement, a nonreactive NST, a positive CST and a poor biophysical profile.
The frequency and timing of fetal surveillance depend on the severity of the disease and the degree of glycemic control. Frequent ( every 4 to 6 weeks) ultrasound examinations to assess fetal growth should be performed.
In the case of abnormal fetal testing, the practioner should assess gestational age and, if the fetus is found to be mature, should proceed to delivery. If the fetus is intermediate in maturity, amniotic fluid assessment for pulmonary maturity may assist in the decision regarding whether delivery should be effected. If the fetus is immature, further testing such as contraction stress tests or hospitalization with continuous fetal heart rate monitoring is advised.
Preterm labor is increased in patients with diabetes and they should be treated with magnesium sulfate as the initial tocolytic agent because the beta mimetics markedly influence glucose control. Corticosteroids increase maternal glucose levels, and this therapy may consist of continuous insulin infusion in certain cases.
Intrapartum and Postpartum Management
Induction of labor is recommended at 38 weeks in patients with poor glucose control and macrosomia. Insulin-requiring diabetics should be induced at 40 weeks’ gestation if spontaneous labor has not occurred.
Induction of labor may be attempted if the fetus is not excessively large and if the cervix is capable of being induced( i.e., if the cervix is soft, appreciably effaced, and somewhat dilated).
The possibility of shoulder dystocia in the macrosomic infant of a mother with diabetes must be considered; cesarean section may be indicated to avoid the trauma of a delivering of a large infant(>4000g). Euglycemia should be maintained during labor.
Women diagnosed with gestational diabetes have an increased risk of developing diabetes mellitus in the future. If they require insulin for their pregnancy, there is a 50% risk of diabetes within 5 years. If dietary control has been sufficient, a 60% risk of developing diabetes mellitus within 10-15 years still persists.
For this reason, all gestationally diabetic patients should have a 75-g 3-hr glucose tolerance to evaluate for preexisting diabetes. If the 1-hr value is high, it represents decreased insulin capacity, whereas an elevated 3-hr value reflects decreased insulin receptors. In the former, limiting simple sugars in the diet should become a lifetime goal. In the latter, weight loss with increased abdominal musculature should significantly reduce the increased risk of diabetes.
Question 1: The infant of a diabetic mother is NOT at risk for which of the following?
(A) Increased perinatal death rate
(B) Hypocalcemia
(C) Hyperglycemia
(D) Neural tube defects
(E) Macrosomia
Question 2: Glucosuria in urine samples during routine prenatal visits indicates:
(A) Gestational diabetesQuestion 3: A 1-hour glucose tolerance test in a woman with a previous stillborn infant resulted in the following value: 1-hour blood sugar = 140mg/dL. Follow-up for this patient should include which of the following?
(A) Nothing furtherAnswer 1: C . The effects of diabetes on the fetus and infant can be considerable, especially in uncontrolled diabetes. There is an increase in fetal abnormalities such as neural tube defects. Macrosomia is common, and the perinatal death rate is higher than normal. The newborn may show hypocalcemia and hypoglycemia( not hyperglycemia). The insulin secretion that has been stimulated in the fetus by the high levels glucose from the mother continues after birth and can drop the newborn blood glucose to dangerously low levels.
Answer 2: B. Glucosuria is most often secondary to the pregnancy-related glomerular filtration of glucose without an increased tubular reabsorption. The finding of glucose in the urine of a pregnant woman does not mean that she has gestational diabetes. However, it is an indication to perform glucose testing because gestational diabetes is a distinct possibility. The initial test would be a 1-hour screening test and not the 3-hour test, which is only done if the 1-hour glucose tolerance test is abnormal. It is unnecessary to control dietary glucose intake strictly without a diagnosis of gestational diabetes. Likewise, small doses of insulin would be unnecessary in the absence of a diagnosis of diabetes.
Answer 3: C . The screening 1-hour glucose tolerance test was ordered because of the woman’s history of a stillborn infant. In a woman with a history of unexplained fetal death, there should be a high index of suspicion of diabetes. Although the 1-hour test result results were abnormal, a diagnosis of gestational diabetes cannot be made on that value alone; therefore, there is no immediate need for dietary control or postprandial blood sugar monitoring. However, the abnormal 1-hour test results should be followed up by a standard 3-hour glucose tolerance test. If two or more of the four results are abnormal,the patient is diagnosed as having gestational diabetes. In addition, even if the patient is diagnosed as diabetic, the degree of glucosuria in a patient with diabetes does not reflect plasma glucose values.
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