Overview
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy (1).  The definition applies regardless of whether insulin is used for treatment or the condition persists after pregnancy.  It does not exclude the possibility that the glucose intolerance may have antedated the pregnancy (2).  Approximately 7% of all pregnancies are complicated by GDM (1).

Nutrition Assessment and Diagnosis
A risk assessment for GDM should be performed during the first prenatal visit (1,2).  Women with clinical characteristics consistent with a high risk of GDM (marked obesity, personal history of GDM, glycosuria, or strong family history of diabetes) should undergo glucose testing as soon as feasible (1,2).  If this initial screening does not detect GDM, the test should be repeated between 24 and 28 weeks of gestation (1).  All pregnant women of average risk should be screened between the 24th and 28th week of pregnancy.  Women who have a low-risk status do not require glucose testing; but, low-risk status is limited to women who meet all of the following characteristics (1,2):

• younger than 25 years old
• normal weight before pregnancy
• member of an ethnic group with a low prevalence of diabetes
• no known diabetes in first-degree relatives
• no history of abnormal glucose tolerance
• no history of poor obstetric outcome

    All pregnant women of average-risk status should have a screening glucose load between the 24th and 28th week of pregnancy.  For this test, 50 g of oral glucose is given without regard to the time of the last meal or the time of day.  A value of 1-hr blood glucose level greater than 130 or 140 mg/dL is the recommended threshold to indicate the need for a full diagnostic glucose tolerance test (1).  The diagnosis of GDM is based on the results of the 100-g oral glucose tolerance test; these results are interpreted according to the diagnostic criteria of O’Sullivan and Mahan, as modified by Carpenter and Coustan for current glucose assay techniques (1,2).  A definitive diagnosis requires that two or more of the venous plasma glucose concentrations meet or exceed the following values: fasting, 95 mg/dL; 1 hour, 180 mg/dL; 2 hours, 155 mg/dl; and 3 hours, 140 mg/dL (1,2).  See Diagnostic Criteria for Diabetes Mellitus.

    The results of the Hyperglycemia and Adverse Pregnancy Outcomes study were recently reported at the American Diabetes Association’s 67th Scientific Session.  This large-scale, multinational, epidemiologic study demonstrated that the risk of adverse maternal, fetal, and neonatal outcomes continuously increased as a function of maternal glycemia at 24 to 28 weeks of gestation, even within ranges previously considered to be normal for pregnancy.  For most complications, there was no threshold for risk.  These results may call for a careful reconsideration of the diagnostic criteria for GDM (3).

Clinical Monitoring
Maternal metabolic monitoring should be directed at detecting hyperglycemia severe enough to increase risks to the fetus (4).  Fasting hyperglycemia (>105 mg/dL) may be associated with an increased risk of intrauterine fetal death during 4 to 8 weeks of gestation (1). For both GDM and preexisting diabetes, self-monitoring of blood glucose levels is essential for the management of diabetes during pregnancy.  Urine should also be tested for ketones on a routine basis, and these test results can be used to detect insufficient energy or carbohydrate intake in women treated with energy restriction (1-4).  Monitoring the urine glucose levels is not appropriate in GDM (1).  The patient’s blood pressure and urine protein levels should be monitored to detect hypertensive disorders (1).  Monitoring schedules for patients with preexisting diabetes have been developed by the American Diabetes Association (1,3,4).

Nutrition Intervention for Gestational Diabetes Mellitus
All women with GDM should receive nutrition counseling by a registered dietitian, which is consistent with the recommendations of the American Diabetes Association (1,3,4).  Medical nutrition therapy for GDM primarily involves a carbohydrate-controlled meal plan that promotes optimal nutrition for maternal and fetal health with adequate energy for appropriate gestational weight gain, achievement and maintenance of normoglycemia, and the absence of ketosis (4).  Specific therapeutic goals are based on an individual nutrition assessment and self-monitoring of blood glucose levels.  Optimum neonatal outcomes occur more frequently in women who gain the recommended amount of weight based on prepregnancy body mass index (BMI) levels established by the Institute of Medicine (5) (Grade I). 

Overweight and obese women with GDM benefit from nutrition counseling by a dietitian to decrease the rate of weight gain, decrease the levels of fasting and postpartum serum glucose, and normalize infant birth weight (5) (Grade I).  Weight loss is not recommended during pregnancy; however, modest energy and carbohydrate restriction may be appropriate for overweight and obese women with GDM (4).  Refer to Table C-1 for the current weight gain guidelines (6-8).

Sources: Subcommittee on Nutritional Status and Weight Gain During Pregnancy, Committee of Nutritional Status During Pregnancy and Lactation, Food and Nutrition Board, Institute of Medicine, National Academy of Sciences. Nutrition During Pregnancy.  Washington, DC: National Academy Press; 1992.
Brown JE, Carlson M.  Nutrition and multifetal pregnancy.  J Am Diet Assoc.  2000;100:343-348.

Energy Requirements
The MNT should include adequate energy and nutrients to meet the needs of pregnancy and should be consistent with the maternal blood glucose goals.  Cohort studies show that energy requirements are highly variable and can be met by increasing food intake, decreasing physical activity, or decreasing fat storage.  Therefore, recommendations for energy levels are best determined by monitoring weight gain, physical activity, appetite, daily food intake, and glucose and ketone records (5) (Grade I).  Refer to Table C-2 for the suggested daily energy intake for pregnant diabetic women (1,9). 

Sources: American Diabetes Association.  Gestational diabetes mellitus: position statement.  Diabetes Care.  2004;27(suppl 1):88S-90S.
Medical Management of Pregnancy Complicated by Diabetes.  2nd ed.  Alexandria, Va: American Diabetes Association; 1995.

Managing Ketosis
The prevention of ketosis is a primary outcome of medical nutrition therapy in GDM (1).  Case-control and cohort studies have found an association between ketonemia and ketonuria during GDM and a lower intelligence quotient in offspring (5) (Grade II).  Ketone testing is an important part of self-monitoring and aids in adjusting the energy intake level, carbohydrate distribution, and physical activity level (5) (Grade II).  To prevent ketosis, adequate energy intake and the appropriate distribution of meals and snacks is important.  An evening snack may be needed to prevent accelerated ketosis overnight (4).  Low-energy diets in obese women with GDM can result in ketonemia and ketonuria (4).   Randomized controlled trials have shown that restricting energy intake to 1,200 kcal/day in obese women (BMI >30 kg/m2) with GDM results in ketonemia or ketonuria, whereas restricting the daily energy intake to a more liberal amount of ~1,800 kcal (25 kcal/kg of actual weight) does not result in ketonemia or ketonuria (5) (Grade I).  Moderate energy restriction, defined as a 30% reduction in estimated energy needs, in obese women with GDM may improve glycemic control and reduce excessive maternal weight gain without the development of ketonemia; however, insufficient data are available to determine the effect of such diets on perinatal outcomes (4).  Daily food records, weekly weight checks, and ketone testing remain paramount in assessing the adequacy of a patient’s energy intake (4).   

Carbohydrate Intake
The amount and kind of carbohydrate in meals and snacks are key to maintaining optimal blood glucose levels and reducing the need for insulin while controlling maternal weight gain and infant birth weight (4,5,10) (Grade II).  The amount and distribution of carbohydrate intake should be based on the clinical outcome measures of hunger, plasma glucose levels, weight gain, and ketone levels (4).  A minimum of 175 g of carbohydrate should be provided on a daily basis (4).   A diet comprised of 42% to 45% carbohydrate distributed among six to eight meals and snacks throughout the day with smaller amounts of carbohydrate (15 to 45 g) at breakfast and snacks promotes normal blood glucose levels (5) (Grade II).  Lower carbohydrate intake is suggested at breakfast, because carbohydrate is generally less well tolerated at breakfast than at other meals during pregnancy (4).  It has been suggested that nonnutritive sweeteners may be used in moderation as a means to control total energy intake and promote blood glucose control in GDM (1).  While there are recognizable benefits of the use of nonnutritive sweeteners with maintenance of blood glucose control, there is limited evidence to support the use or nonuse of nonnutritive sweeteners in pregnancy and even less evidence addressing this issue specifically in GDM (5) (Grade IV).  Refer to Nutrition Management During Pregnancy and Lactation for additional information about the nutrient requirements and use of nonnutritive sweeteners during pregnancy.

Self-Monitoring of Blood Glucose Goals
Self-monitoring of blood glucose levels is an essential component of maintaining desirable blood glucose levels in women with GDM.  Studies have shown that the best outcomes are achieved when both fasting and 1- or 2-hour postprandial blood glucose levels are monitored three to eight times per day and used to modify food intake or meal patterns and physical activity levels (5) (Grade I).  The American Diabetes Association recommends that people with type 1 diabetes and pregnant women who take insulin check their blood glucose levels three or more times daily so that they can adjust their food intake, physical activity level, and/or insulin dosage to meet blood glucose goals (3).  The following table provides the goals for blood glucose management (1).  Evidence has shown that mean serum glucose levels of 86 mg/dL increase the risk for small for gestational age infants and that mean glucose levels of 105 mg/dL increase the risk for macrosomia (5) (Grade I).

Source: American Diabetes Association.  Gestational diabetes mellitus: position statement.  Diabetes Care.  2004;27(suppl 1):88S-90S.

    The newer models of glucose meters are often plasma calibrated.  Plasma-calibrated meters usually read 10% to 15% higher than whole-blood glucose meters. Therefore, healthcare providers and patients should be aware of which test is being used to measure glucose levels (1,4).  Plasma meters also allow the patient to test glucose levels at other sites, such as the thigh, arm, or calf.  To account for differences in blood glucose levels from different sites, plasma glucose is measured instead of whole-blood glucose because the values are more consistent from site to site.

Medication Management  
Insulin therapy is recommended if medical nutrition therapy fails to maintain the following self-monitored glucose levels: a fasting plasma glucose level of ≤105 mg/dL, a 1-hour postprandial blood glucose level of <155 mg/dL, and/or a 2-hour postprandial plasma glucose level of ≤130 mg/dL (1,5) (Grade I).  Human insulin should be used when insulin is prescribed, and self-monitoring blood glucose records should guide the dosage and timing of insulin therapy.  The use of insulin analogs has not been adequately tested in patients with GDM.  If insulin therapy is added to nutrition therapy, a primary goal must be to maintain consistent carbohydrate intake at meals and snacks to facilitate insulin adjustments (4).  The prevention of ketosis may require multiple daily insulin injections and the distribution of dietary carbohydrate into small frequent meals (three meals and three or four snacks).  Insulin requirements normally increase as the pregnancy proceeds, and the insulin regimen must be continually adjusted throughout the pregnancy.  Blood glucose monitoring by the patient is an essential part of this process (1,4,10).  The heightened insulin requirement will plummet within hours of delivery.  Metabolic control during labor, delivery, and the postpartum period should be managed by frequent determinations of blood glucose levels and adjustments to the insulin dose.

A number of drugs commonly used in the treatment of patients with diabetes may be relatively or absolutely contraindicated during pregnancy (3).  Statins and angiotensin-converting enzyme inhibitors, which are used to manage disorders in lipid metabolism or hypertension, should be discontinued prior to conception (3).  Among the oral antidiabetic drugs, metformin and acarbose are classified as category B drugs (no evidence of risk in humans), while all other oral antidiabetic drugs including sulfonylureas (eg, glyburide) are classified as category C drugs (risk cannot be ruled out) (1,3,4).  The potential risks and benefits of oral antidiabetic agents in the preconception period must be carefully evaluated, recognizing that data are insufficient to establish the safety of these agents in pregnancy (3). Particularly for patients with preexisting diabetes, medication evaluation should be carefully assessed as part of preconception care (3).

Physical Activity

Regular physical activity reduces insulin resistance, lowers fasting and postprandial glucose concentrations, and may be used as an adjunct to nutrition therapy to improve maternal glycemia (4,5) (Grade II).  The optimal frequency and intensity of exercise for lowering maternal glucose concentrations have not been determined; but, it appears that a minimum of three weekly exercise sessions, each longer than 15 minutes, is required to modify maternal glucose levels.  In addition, 2 to 4 weeks of regular exercise may be required before a reduction of glycemia occurs (4).  Regular physical activity has also been shown to reduce excessive weight gain during pregnancy (5) (Grade II).  Persons should frequently monitor their blood glucose levels before and after physical activity.  Persons who do exercise should be aware that prolonged exercise (> 60 minutes) is more likely to cause hypoglycemia in pregnancy (5) (Grade II).

Follow-up Evaluation and Monitoring

The recurrence rate of GDM in subsequent pregnancies is 30% to 65% (5) (Grade I).  The American Diabetes Association recommends a follow-up evaluation of each woman diagnosed with gestational diabetes (1,4), because these women may be prone to the development of type 2 diabetes later in life (4) (Grade I).  Reclassification of maternal glycemic status should be performed 6 to 12 weeks after delivery (3).  If postpartum glucose levels are normal, then glycemia should be reassessed at a minimum of 3-year intervals (3).  Women with impaired fasting glucose or impaired glucose tolerance in the postpartum period should be annually tested for diabetes (1).  See Diagnostic Criteria for Diabetes Mellitus.  It is prudent to provide nutrition counseling and guidance to these women after the birth of their children.  Lifestyle modifications aimed at reducing weight or preventing weight gain and increasing physical activity after pregnancy are recommended to reduce the risk of developing type 2 diabetes mellitus (3). 

Dietary Recommendations for Pregnant Women With Preexisting Diabetes
Preconception care is a key factor in successful pregnancy outcomes for persons with preexisting diabetes (type 1 or type 2).  All women with diabetes should be educated regarding the need for good blood glucose control before pregnancy and should participate in family planning (3).  A woman’s A1C level should be as close to normal as possible (<7%) before conception is attempted (3).  Medication use should be evaluated before conception because drugs commonly used to treat diabetes and its complications may be contraindicated or not recommended in pregnancy (3).  Nutrient requirements during pregnancy and lactation are similar for women with and without diabetes (4).  For pregnancy complicated by diabetes, nutrition therapy should attempt to achieve and sustain optimal maternal blood glucose control.  A favorable pregnancy outcome is defined as a gestational duration of 39 to 41 weeks and the birth of a live infant weighing 6.6 to 8.8 lb (3 to 4 kg) (7).  During pregnancy with prior onset of type 1 or type 2 diabetes, the distribution of energy intake and carbohydrates in the meal plan should be based on the woman’s eating habits, blood glucose records, and stage of pregnancy.  Regular meals and snacks are important to avoid hypoglycemia due to the continuous fetal draw of glucose from the mother (4).  An evening snack is usually necessary to decrease the potential for overnight hypoglycemia and fasting ketosis (4).  Energy intake to achieve appropriate weight gain may be estimated based on the percent of desirable body weight before the pregnancy (1,4).  Pregravid BMI may be used to estimate a goal for weight gain during pregnancy (6-8).

Lactation
Breast-feeding is recommended for infants of women with preexisting diabetes or GDM.  Successful lactation requires planning and coordination of care (11).  In most situations, breast-feeding mothers require less insulin because of the energy expended by nursing.  Lactating women have reported fluctuations in blood glucose levels related to nursing sessions, and they often require a carbohydrate-containing snack before or during nursing sessions (11).

References

1. American Diabetes Association.  Gestational diabetes mellitus: position statement.  Diabetes Care.  2004;27(suppl 1):88S-90S.
2. American Diabetes Association.  Diagnosis and classification of diabetes mellitus:  position statement.  Diabetes Care.  2008;31(suppl 1): 55S-60S.
3. American Diabetes Association.  Standards of medical care in diabetes—2008.  Diabetes Care.  2008;31(suppl 1): 12S-54S.
4. American Diabetes Association.  Nutrition recommendations and interventions for diabetes: position statement.  Diabetes Care.  2008;31 (suppl 1):61S-78S.
5. Diabetes 1 and 2 Evidence Analysis Project.  American Dietetic Association Evidence Analysis Library. American Dietetic Association; 2008.  Available at: http://www.adaevidencelibrary.com. Accessed January 1, 2008. 
6. Food and Nutrition Board.  Nutrition During Pregnancy.  Part I: Weight Gain.  Part 2: Nutrient Supplements.  Washington, DC: Institute of Medicine, National Academy of Sciences; 1990.
7. Subcommittee on Nutritional Status and Weight Gain During Pregnancy, Committee of Nutritional Status During Pregnancy and Lactation, Food and Nutrition Board, Institute of Medicine, National Academy of Sciences. Nutrition During Pregnancy.  Washington, DC: National Academy Press; 1992.
8. Brown JE, Carlson M.  Nutrition and multifetal pregnancy.  J Am Diet Assoc.  2000;100:343-348.
9. Medical Management of Pregnancy Complicated by Diabetes.  2nd ed.  Alexandria, Va: American Diabetes Association; 1995.
10. Major CA, Henry MJ, De Veciana M, Morgan MA.  The effects of carbohydrate restriction in patients with diet-controlled gestational diabetes.  Obstet Gynecol.  1998;91:600-604.
11. Reader D, Franz MJ.  Lactation, diabetes, and nutrition recommendations.  Curr Diab Rep.  2004;4:370-376.

Bibliography
ACOG Practice Bulletin. Clinical management guidelines for obstetrician-gynecologists. No. 30, September 2001 (replaces Technical Bulletin No. 200, December 1994). Gestational diabetes.  Obstet Gynecol.  2001;98:525-538.
Suitor CW.  Nutrition for women in their childbearing years: a review of the literature and a summary of expert recommendations.  Nutr Clin Care.  1999;2:11-45.

Manual of Clinical Nutrition Management                                                     
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