In 1995, Moses et al assessed the prevalence of gestational diabetes mellitus in patients with various risk factors and recommended universal testing.Gestational diabetes mellitus was diagnosed in 6.7% of the women overall, in 8.5% of the women aged 30 years or older, in 12.3% of the women with a preconception body mass index of 30 kg/m2 or greater, and in 11.6% of women with a family history of diabetes in a first-degree relative. A combination of one or all of these risk factors predicted gestational diabetes mellitus in 61% of cases. Gestational diabetes mellitus was present in 4.8% of the women without risk factors.
A nested case-control study indicated that another risk factor for the development of gestational diabetes is the presence of hypertension before pregnancy or during early pregnancy. The report, which looked at 381 women with hypertension or prehypertension (the latter being defined in the study as 120-139/80-89 mmHg), as well as at 942 control subjects, found that prehypertension before or during early pregnancy was associated with a slightly increased risk of gestational diabetes, but hypertension was associated with a twofold increase in risk.
High cholesterol and egg intake prior to and during pregnancy increase the risk of gestational diabetes.
American Diabetes Association recommendations
The current recommendations from the American Diabetes Association "Standards of Medical Care in Diabetes--2010" are to conduct a risk assessment for all pregnant women at the first prenatal visit.[4, 5] Women who are at very high risk should undergo testing as soon as possible, in order to identify those with occult type 2 diabetes, using the standard diagnostic approach to diabetes (see Preexisting Diabetes Diagnosis, below). Criteria for very high risk are as follows:
Gestational diabetes mellitus during a previous pregnancy or delivery of an LGA infant
Presence of glycosuria
Diagnosis of polycystic ovarian syndrome
Strong family history of type 2 diabetes
All pregnant women should be screened for gestational diabetes at 24-28 weeks' gestation—including those with negative test results in the first trimester—unless they are at low risk. To be considered at low risk, a woman must meet all of the following criteria:
Age < 25 years
Weight normal 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
The best method for screening for gestational diabetes continues to be controversial. The 2-step system is currently recommended in the United States. A 50-g, 1-hour glucose challenge test (GCT) is followed by a 100-g, 3-hour oral glucose tolerance test (OGTT) for those with an abnormal screening result. Alternatively, for high-risk women, or in areas in which the prevalence of insulin resistance is 5% or higher (eg, the southwestern and southeastern United States), a 1-step approach can be used by proceeding directly to the 100-g, 3-hour OGTT.
The sensitivity of gestational diabetes mellitus testing depends on the threshold value used for the 50-g glucose challenge. Current recommendations from the American Diabetes Association "Standards of Medical Care in Diabetes--2010"[4, 5] and the American College of Obstetricians and Gynecologists (ACOG) note that a threshold value of 140 mg/dL results in approximately 80% detection of gestational diabetes, whereas a threshold of 130 mg/dL results in 90% detection. A potential disadvantage of using the lower value of 130 mg/dL is an approximate doubling in the number of OGTTs performed.
Meltzer et al found that 2-step screening with a 1-hour, 50-g glucose screen, followed by (if necessary) an OGTT, was superior to 1-step screening with a 75-g OGTT. In a prospective, randomized, controlled trial, the total cost per woman screened was lower with the 2-step approach, because many patients with gestational diabetes were diagnosed on the basis of a glucose screen result of 10.3 mmol/L (185.4 mg/dL) or greater, thus obviating the additional blood draws and time required for the OGTT.
Other tests (eg, maternal HbA1C, random postprandial or fasting blood sugar level, or fructosamine level) are not recommended because of low sensitivity.
Patients undergoing oral glucose tolerance testing for gestational diabetes should undertake carbohydrate loading for 3 days preceding the test (>150 g carbohydrates) and an overnight fast of 8–14 hours the night before. The patient should remain seated during the test, and should not smoke. Two or more glucose values, as listed in the table below, must be met or exceeded for the diagnosis of gestational diabetes.
Table 2. Plasma Glucose Criteria for Gestational Diabetes (Open Table in a new window)
|Time||100 g Glucose Load,
|1 hour||180 (10.0)|
|2 hours||155 (8.6)|
|3 hours||140 (7.8)|
Patients with a single abnormal value on a 3-hour OGTT are likely to exhibit some degree of glucose intolerance. Left untreated, these patients are at higher risk for fetal macrosomia and neonatal morbidity. Consequently, patients with a single abnormal value should receive dietary and physical activity counseling. If the abnormal value on the OGTT was obtained before 26 weeks' gestation, a repeat OGTT should be performed approximately 4 weeks later.
Whether administered at 12 or 26 weeks’ gestation, the GCT can be performed without regard to recent food intake (ie, nonfasting state). Indeed, results from tests performed in fasting subjects are more likely to be falsely elevated than results from tests conducted between meals.
In a systematic review performed for the US Preventive Services Task Force, Donovan and colleagues found that by 24 weeks’ gestation, the 50-g oral glucose challenge test (GCT) and fasting plasma glucose level (at a threshold of 85 mg/dL) are effective for ruling out the presence of gestational diabetes mellitus in pregnant women and that the oral GCT is better for confirming its presence.[49, 50]
Type 1 Diabetes
Patients with type 1 diabetes are typically diagnosed during an episode of hyperglycemia, ketosis, and dehydration; this occurs most commonly in childhood or adolescence, before pregnancy. Type 1 diabetes is rarely diagnosed during pregnancy; in these cases, patients most often present with unexpected coma, because early pregnancy may provoke diet and glycemic control instability in patients with occult diabetes. A pregnancy test should be ordered in all reproductive-aged women admitted to the hospital for blood sugar management.
Type 2 Diabetes
It can be difficult to distinguish gestational diabetes mellitus from type 2 diabetes that preceded pregnancy but was unrecognized, or whose onset occurred during pregnancy. Traditionally, the distinction has been based on whether the diabetes persisted after delivery. However, the International Association of Diabetes and Pregnancy Study Groups now recommends that high-risk women who are found to have diabetes at their initial prenatal visit, according to standard diagnostic criteria, receive a diagnosis of overt diabetes rather than gestational diabetes.
According to the American Diabetes Association "Standards of Medical Care in Diabetes--2010,"[4, 5] the presence of any one of the following criteria supports the diagnosis of diabetes mellitus:
HbA1C = 6.5%
Fasting plasma glucose greater than 126 mg/dL (7.0 mmol/L); fasting is defined as no caloric intake for at least 8 hours
A 2-hour plasma glucose level = 200 mg/dL (11.1 mmol/L) during a 75-g OGTT
A random plasma glucose level = 200 mg/dL (11.1 mmol/l) in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis
In the absence of unequivocal hyperglycemia, a diagnosis based on any of the first 3 of the above criteria should be confirmed by repeat testing on a different day.
Despite advanced age, multiparity, obesity, and social disadvantage, patients with type 2 diabetes were found to have better glycemic control, fewer large for gestational age infants, fewer preterm deliveries, and fewer neonatal care admissions compared with patients with type 1 diabetes. This suggests that better tools are needed to improve glycemic control in patients with type 1 diabetes.
Prediabetes is a term used to distinguish people who are at increased risk of developing diabetes. People with prediabetes have impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). Some people may have both impaired fasting glucose and impaired glucose tolerance.
Impaired fasting glucose is a condition in which the fasting blood sugar level is elevated (100-125 mg/dL) after an overnight fast but is not high enough to be classified as diabetes. Impaired glucose tolerance is a condition in which the blood sugar level is elevated (140-199 mg/dL after a 2-h OGTT) but is not high enough to be classified as diabetes.
Women with prediabetes identified before pregnancy should be considered at extremely high risk of developing gestational diabetes mellitus during pregnancy. As such, they should receive early (first-trimester) diabetic screening. Prediabetes, impaired fasting glucose, and impaired glucose tolerance are not meaningful terms in prenatal management, unless patients exceed the plasma glucose limits for diagnosing gestational diabetes mellitus.
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