Gestational diabetes: Is your patient at risk?

Screening most pregnant women between 24 and 28 weeks of gestation is the standard of care. It is important for clinicians to identify and treat gestational diabetes early to improve perinatal outcomes.

Shalonda Pettis, PA-C

The author works at The Doctor’s Office, Stockbridge, Ga. She has indicated no relationships to disclose relating to the content of this article.

CME Earn Category I CME credit by reading this article and "Nine key questions to address polypharmacy in the elderly" and successfully completing the post-test. Successful completion is defined as a cumulative score of at least 70% correct. This material has been reviewed and is approved for 1 hour of clinical Category I (Preapproved) CME credit by the AAPA. The term of approval is for 1 year from the publication date of May 2005.

Gestational diabetes mellitus (GDM) is defined as “carbohydrate intolerance of varying severity with onset or first recognition during pregnancy. This definition applies whether insulin is used for treatment or the condition persists after pregnancy. It does not exclude the possibility that unrecognized glucose intolerance may have antedated the pregnancy.”¹ The prevalence of GDM varies worldwide, comprising from 1% to 14% of all pregnancies depending on the population studied and the diagnostic tests employed.^2,3 GDM is more likely to develop in certain groups of women, including those with a family history of type 2 diabetes, advanced maternal age, obesity (body mass index greater than 27 kg/m²), and nonwhite ethnicity. African American, Hispanic American, and Native American women, as well as those from the Indian subcontinent, appear to be at greater risk for GDM.^4,5

Early identification is of obvious importance. Fetal growth and development depends upon the normal delivery of nutrients, particularly glucose. The infants of women with GDM may experience macrosomia, neonatal hypoglycemia, hypocalcemia, hypomagnesemia, hyperbilirubinemia, dystocia, birth trauma, and fetal anomalies. Mothers are at an increased risk of hypertension, preeclampsia, urinary tract infections, cesarean delivery, and type 2 diabetes.⁶ Manifestations of GDM are related to serious adverse outcomes and thus warrant particular attention. Although controversy exists over which patients need screening, clinicians do agree that excellent blood glucose control will improve perinatal outcomes.⁵

Pathophysiology of GDM

GDM is pathophysiologically similar to type 2 diabetes. A number of changes occur during normal pregnancy that may predispose a woman to the development of GDM. Because of the increased secretion of hormones with metabolic effects on glucose tolerance, pregnancy is a diabetogenic condition. Hormones with diabetogenic effects include estrogen, prolactin, human chorionic somatomammotropin, human placental lactogen, cortisol, and progesterone.^7,8 As the hormonal changes occur, insulin resistance can develop. The insulin resistant state peaks during the third trimester, leading to greater than normal secretion of insulin in order to maintain euglycemia.^5,8 If the mother’s pancreas is unable to produce enough insulin to counteract her resistance to it, maternal blood glucose levels increase and GDM occurs. GDM usually disappears after pregnancy because changes in these hormones are no longer present.

Screening procedures: Risk stratification

Whether universal or selective screening should be the standard of care has been a matter of debate for several years. Historically, clinicians relied on risk factors to determine the need for screening: The clinician performed a risk assessment for GDM at the first prenatal visit, and only women who appeared to be at increased risk would go on for further testing. Screening recommendations now vary among different organizations. There are three categories of risk: low, average, and high. The United States Preventive Services Task Force (USPSTF) has stated, “There is insufficient evidence to recommend for or against universal screening for gestational diabetes.”⁹ The USPSTF has concluded, however, that screening high-risk women may be beneficial.

Women with a high risk for GDM should undergo glucose testing as early in pregnancy as possible. Having any of these characteristics puts a woman at high risk:
•   Marked obesity
•   Personal history of GDM
•   Strong family history of type 2 diabetes mellitus
•   Repetitive glycosuria.⁵

If the practitioner does not diagnose GDM at the initial screening, the patient should be retested between 24 and 28 weeks of gestation.

Low-risk women are generally described as having all of the following characteristics:
•   Age younger than 25 years
•   Normal weight before pregnancy
•   Member of an ethnic group with a low prevalence of GDM
•   No known diabetes in first-degree relatives
•   No history of abnormal glucose tolerance
•   No history of poor obstetric outcome.¹

The American Diabetes Association (ADA) has proposed that women at low risk do not require glucose testing (see Table 1).¹⁰ Note that average-risk patients are women who are not at low risk but also do not meet the criteria to be considered at high risk for GDM. There is a consensus that these patients should be screened between 24 and 28 weeks of gestation.

Despite the lack of evidence to recommend universal screening for GDM, screening all pregnant women has several benefits. Early testing can help prevent some diabetes-related complications. Appropriate management can reduce the occurrence of fetal macrosomia and associated birth trauma.^4,5 Also, since women with GDM are at increased risk for developing type 2 diabetes, screening would identify these women and permit intervention to prevent or delay the onset of the disease. Because of these benefits, many clinicians are performing universal screening.

The American College of Obstetricians and Gynecologists, the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, and the Fourth International Workshop-Conference on Gestational Diabetes Mellitus all recommend that screening for GDM be carried out between 24 and 28 weeks of gestation.⁴ Women with GDM should be identified as early as possible in order to ensure time for intervention.

Diagnostic testing

Glucose testing There are two ways to approach screening for GDM. The one-step approach involves performing a diagnostic oral glucose tolerance test (OGTT), the result of which confirms or excludes the diagnosis of GDM. The two-step approach involves performing an oral glucose challenge test (OGCT) initially and, if the result is positive, proceeding to the OGTT.

The OGCT consists of a 50-g oral glucose load, followed by a plasma glucose determination 1 hour later.⁴ This test can be performed without regard to time of day or previous meal ingestion.¹ A glucose value of 140 mg/dL or greater is considered abnormal and necessitates a full diagnostic OGTT.⁵ For the OGTT, the patient fasts for 8 to 10 hours overnight and receives a 100-g glucose load after a glucose level is obtained. Blood is drawn every hour for the next 3 hours.⁶ GDM is diagnosed when two or more of the values listed in Table 2 are met or exceeded.

The glucose values used to detect GDM were first determined by O’Sullivan and Mahan, revised by the National Diabetes Data Group, and later modified by Carpenter and Coustan.^5,10 The ADA endorses the Carpenter and Coustan criteria.¹⁰ Alternatively, the diagnosis of GDM can be made using a 75-g glucose load. The corresponding glucose threshold values are listed in Table 3. This test is considered less desirable because it is not as well validated as the 100-g OGTT for the detection of at-risk infants or mothers.⁶

Obstetric and perinatal considerations The presence of fasting hyperglycemia (glucose level greater than 105 mg/dL) may be associated with an increased risk of intrauterine fetal death during the last 4 to 8 weeks of gestation.⁵ More commonly, fetal macrosomia, a serious condition with grave complications, occurs with increased severity of GDM. Macrosomic infants have enlarged internal organs, including liver, heart, pancreas, and adrenal glands.¹¹ Labor and delivery complications may result from fetal macrosomia, and cesarean delivery may be indicated to avoid trauma from a large infant (weighing more than 4,500 g). Neonatal jaundice, polycythemia, and hypocalcemia may occur as well.¹⁰

Patients with GDM may be at an increased risk for hypertensive disorders.² Although hypertension in pregnancy has multiple definitions, chronic hypertension is defined as high BP that is either present before pregnancy or diagnosed before the 20th week of gestation. Preeclampsia, increased BP in association with proteinuria, edema, or both, generally occurs after 20 weeks of gestation.¹¹ The incidence of preeclampsia is doubled in women with GDM, especially in those who have nephropathy.⁵

Monitoring, management, and follow-up

Antepartum dietary therapy Once the diagnosis of GDM is made, appropriate management must be initiated. Patients should be seen every 1 to 2 weeks to monitor response to therapy until a state of euglycemia is reached. Dietary therapy is the key element in treating patients with GDM.¹² Medical nutrition therapy (MNT) should include adequate amounts of calories and nutrients for the fetus and the mother. The diet typically consists of approximately 2,200 calories per day, with an emphasis on high-fiber complex carbohydrates, which are recommended because simple sugars have a tendency to increase postprandial blood glucose levels.¹ The caloric prescription is based on the patient’s prepregnancy weight, with 30 kcal/kg for the average patient, 35 kcal/kg for the underweight patient, and 25 kcal/kg for the obese patient.⁵ Urine ketone monitoring may be helpful in detecting insufficient caloric or carbohydrate intake in women treated with calorie restriction.

Frequent self-monitoring of blood glucose (SMBG) is an essential adjunct to MNT for patients with GDM.¹¹ Patients should check their fasting glucose level, as well as a 1-hour or 2-hour postprandial glucose level after each meal. Another helpful adjunctive therapy is physical exercise. Moderate exercise, such as brisk walking three to four times per week, should be recommended to patients with GDM unless contraindicated.

Insulin Studies show that despite adequate MNT, 39% of patients with GDM will require insulin therapy during their pregnancy.¹³ If dietary therapy has proven inadequate, meaning fasting plasma glucose values are 95 mg/dL or higher, 1-hour values are 130 to 140 mg/dL or higher, or 2-hour values are 120 mg/dL or higher, insulin is required. Treatment with insulin should also be initiated if there are signs of excessive fetal growth despite MNT.¹ The recommended starting insulin dosage is 0.8 U per kg of actual body weight per day in the first trimester, 1 U/kg/d in the second trimester, and 1.2 U/kg/d in the third trimester.¹⁴ The total daily dose of insulin is divided, with two thirds administered in the fasting state as two thirds NPH and one third rapid-acting insulin. The remaining one third of the total dose is given as one half rapid-acting insulin at dinner and one half NPH at bedtime.⁵ Regular insulin or human insulin lispro (Humalog) may be used. The clinician may adjust insulin dosages based on the results of SMBG levels, both fasting and postprandial.

Oral glucose-lowering agents have not generally been recommended during pregnancy because of their potential to cross the placental barrier. However, one randomized, unblinded clinical trial compared the uses of insulin and glyburide (Glucovance, a second-generation sulfonylurea) in women with GDM that did not respond to MNT.¹⁵ Although treatment with either agent resulted in similar perinatal outcomes, the incidence of maternal hypoglycemia was decreased in the patients randomized to glyburide.

Fetal monitoring Nonstress tests (NSTs) can provide fetal assessments at intervals, depending upon clinical picture and treatment mode. Patients who are on diet therapy alone begin testing at 40 weeks of gestation, and the NST is performed biweekly. Those who require insulin or glyburide in combination with diet therapy start fetal surveillance earlier with biweekly NSTs. If the diabetes is well controlled, these patients are allowed to progress to their due date. If the diabetes is poorly controlled, however, an elective delivery may be scheduled at 38 to 39 weeks of gestation.^5,16 Patients who have a history of delivering a stillborn infant undergo fetal surveillance with biweekly NSTs starting at 32 weeks of gestation.⁵ Maternal and fetal surveillance is important in identifying the need for early delivery and prevention of unwanted outcomes.

Intrapartum and postpartum

Controlling maternal glucose levels during labor is important in preventing fetal hyperinsulinemia and subsequent neonatal hypoglycemia. Check blood glucose levels every 1 to 2 hours at the bedside, and maintain them between 80 and 110 mg/dL. Insulin is rarely required to reach this goal.⁵ After delivery, monitor the infant for signs of hypoglycemia, hypocalcemia, and hyperbilirubinemia.

In most women with GDM, normoglycemia will return immediately in the postpartum period, although approximately 15% of patients with GDM will remain glucose intolerant during the postpartum state.⁵ Perform postpartum monitoring throughout the hospital stay. Because of the risk of recurring GDM in subsequent pregnancies and an increased risk of type 2 diabetes, it is important to reclassify maternal glycemic status by 6 weeks postpartum.^10,17 If the results of testing are normal, follow up with the patient at least every 3 years with a fasting glucose level. If the results are abnormal but do not warrant a diagnosis of diabetes, prescribe a diet and exercise regimen, and monitor yearly with fasting glucose levels. Criteria for the diagnosis of type 2 diabetes are listed in Table 4.

Prognosis and prevention

Women who have had GDM have an increased risk of developing type 2 diabetes. If they become insulin-dependent during pregnancy, they have a 50% risk of developing diabetes within 5 years.⁵ Encourage all obese patients to improve their diet and lose weight so that they can significantly reduce their increased risk of type 2 diabetes.¹⁶ Advise patients to seek medical attention if symptoms of hyperglycemia develop and to seek preconception counseling for subsequent pregnancies.¹⁰

Conclusion

GDM complicates the lives of many pregnant women and is a major cause of perinatal morbidity and mortality.¹⁸ Despite the lack of consensus over whom to screen, the clinician should screen patients for GDM between 24 and 28 weeks of gestation. If GDM is present, treatment options include dietary management, exercise, insulin, and oral glucose-lowering agents. With proper management, the practitioner can improve the well-being of both the mother and fetus and reduce the incidence of type 2 diabetes.  

REFERENCES

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