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CME: Women's Health

Managing gestational diabetes

Dugan, Joy A. MPH, DHSc, PA-C; Ma-Crawford, Julianna MPH, PA-C

Author Information
Journal of the American Academy of Physician Assistants: September 2019 - Volume 32 - Issue 9 - p 21-25
doi: 10.1097/01.JAA.0000578760.60265.e0
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Box 1
Box 1

The true prevalence of gestational diabetes in the United States is not known, but one study demonstrated a 7.6% prevalence.1 Particular risk factors, including a history of gestational diabetes, family history of diabetes, and obesity, predispose a pregnant woman to dysglycemia.1 In addition, nonwhite ethnicity, advanced maternal age, higher body mass index (BMI), weight gain in early adulthood, and cigarette smoking may predict increased risk of gestational diabetes.2

Box 2
Box 2

Patients at low risk for gestational diabetes include those who are

  • non-Hispanic
  • white
  • young (age under 30 years)
  • normal BMI (25 kg/m2 or less)
  • no history of glucose intolerance or adverse pregnancy outcomes associated with gestational diabetes
  • no first-degree relative with known diabetes.3

Asian American, Native Hawaiian, Pacific Islander, Hispanic, and black women are at a disproportionately higher risk for gestational diabetes and its complications than non-Hispanic white women.4 In the United States in 2016, the unadjusted prevalence of gestational diabetes was 11.1% for non-Hispanic Asian women, 9.2% for American Indian/Alaska Native women, 8.4% for Native Hawaiian/Pacific Islander women, 6.6% for Hispanic women, 5.3% for non-Hispanic white women, and 4.8% for non-Hispanic black women 4.8%.5

Environmental health also may play a role in gestational diabetes. A study in Rhode Island highlighted how air pollution and land use influence pregnancy complications, and showed that gestational diabetes is positively associated with particulate matter air pollution (at sizes of atmospheric particulate matter that are less than 2.5 micrometers) and proximity to major roadways, but negatively associated with being nearer to the coastline.6


Physiologic insulin resistance occurs during pregnancy because the placenta secretes diabetogenic hormones, such as growth hormone, corticotropin-releasing hormone, human placental lactogen, and progesterone. These hormones cause postprandial hyperglycemia and carbohydrate intolerance, allowing the fetus to consume more nutrients. Insulin-dependent glucose uptake of the fetus and placenta causes a lower fasting blood glucose level in pregnant women with normal glucose metabolism.7

In a normal pregnancy, women have a 60% reduction in insulin sensitivity.8 In women with normal pancreatic function, the pancreas can compensate, secreting enough insulin to compensate for physiologic insulin resistance of pregnancy. Gestational diabetes develops when the pancreas cannot compensate for insulin resistance because of functional beta-cell deficits. The pathophysiology of insulin resistance and defective insulin secretion in patients with gestational diabetes is similar to that seen in patients with type 2 diabetes.9 Women whose glucose tolerance is normal before pregnancy but who develop gestational diabetes in late pregnancy tend to have a subclinical metabolic dysfunction before conception, compared with women who have normal glucose tolerance throughout pregnancy.8


In their Standards of Medical Care in Diabetes, the American Diabetes Association (ADA) recommends testing the following types of patients for gestational diabetes:

  • Those who have risk factors and undiagnosed diabetes at their first prenatal visit
  • Women not previously known to have diabetes; test at 24 to 28 weeks of pregnancy
  • Women with gestational diabetes; test for persistent diabetes at 4 to 12 weeks postpartum, using the oral glucose tolerance test and clinically appropriate nonpregnancy diagnostic criteria
  • Women with history of gestational diabetes should have lifelong screening for development of prediabetes or diabetes, performed at least every 3 years.7

The ADA guidelines are consistent with the US Preventive Services Task Force (USPSTF), which makes a B recommendation (net benefit is moderate to substantial) for gestational diabetes screening in asymptomatic women after 24 weeks of pregnancy.10

The 50-g oral glucose tolerance test typically is administered to women who are at moderate risk, meaning those who do not meet all the low-risk criteria for gestational diabetes.3 If a woman is at high risk for gestational diabetes (two or more risk factors), screening tests can be administered earlier in pregnancy and are repeated at 24 to 28 weeks if results of initial results are normal.3


No consensus exists on the best approach to screen for and diagnose gestational diabetes. The ADA standards offer two diagnostic strategies:

  • “One-step” fasting 75-g oral glucose tolerance test at 1 hour and 2 hours
  • “Two-step” with a nonfasting 50-g glucose load test screen measured at 1 hour, followed by a fasting 100-g oral glucose tolerance test measured at 1, 2, and 3 hours for patients who screened positive with the glucose load test.7

The diagnostic cutoffs differ between the two types of tests.

For the one-step test, a fasting plasma glucose level of 92 mg/dL or greater is diagnostic for gestational diabetes, as is a level of 180 mg/dL or greater after 1 hour or 153 mg/dL or greater after 2 hours.11

For the two-step test, the common cutoff thresholds are 130 mg/dL or greater, or 135 or 140 mg/dL for the 1-hour 50-g glucose load test.7 These cutoffs also are recommended by the American College of Obstetricians and Gynecologists (ACOG).12 For the 100-g, 3-hour oral glucose tolerance test during the second step, the most commonly used thresholds are proposed by Carpenter and Coustan and the National Diabetes Data Group (NDDG).13,14 As seen in Table 1, plasma glucose levels are evaluated before the test, and at 1, 2, 3 hours after administration of the 100-g glucose load. The diagnosis of gestational diabetes is made when one or more glucose values fall at or above the following thresholds. Of note, the Carpenter-Coustan criteria increase the prevalence of diagnosis of gestational diabetes by 30% to 50% compared with NDDG.15

Two-step strategy for diagnosing gestational diabetes7,13,14

Opinions differ on whether to use the one-step or two-step screening test. The one-step screening has been adopted internationally; however, the two-step screening continues to be widely used in the United States. The advantage of the one-step test is that it only requires one office visit compared with two for the two-step test.

The two-step test identifies 5% to 6% of pregnant women as having gestational diabetes.16 Research has shown that the one-step test was associated with a 3.5-fold increase in gestational diabetes prevalence as well as improvements in pregnancy outcomes and cost-effectiveness. The one-step approach proposed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) may create additional burdens, however, such as increased healthcare costs and interventions.17 The NIH's consensus development conference determined that although international standardization with the one-step test has clear benefits, evidence was insufficient to adopt a one-step approach; the conference recommended that the two-step test be continued.16

The fasting plasma glucose level or oral glucose tolerance test are better for diagnosing gestational diabetes than an A1C level.3 During pregnancy, physiologic changes occur in red blood cell kinetics and glycemic parameters. A1C falls due to physiologic increase in red blood cell turnover and some degree of physiologic dilution anemia. In addition, A1C alone also fails to capture a measurement of postprandial hyperglycemia.7


Lifestyle modification is the first resource in managing a patient with gestational diabetes. A registered dietitian can develop an individualized food plan with the patient to promote optimal caloric intake for fetal/neonatal and maternal health, the achievement of glycemic goals, and appropriate gestational weight gain.7

Studies also show that any physical activity before and during pregnancy reduces the risk of gestational diabetes.18 Women who engaged in more than 4 hours per week of physical activity had a 76% reduction in gestational diabetes risk compared with inactive women.18 Lifestyle modifications that include diet and exercise changes may be enough to treat gestational diabetes; however, if these do not help the patient achieve the glycemic target, medications may be added.

Insulin is the first-line pharmacologic therapy for gestational diabetes. Multiple daily insulin injections or continuous subcutaneous insulin infusions are comparable options.7 Unlike metformin and sulfonylureas such as glyburide, insulin does not cross the placenta at a measurable level. The combination of dietary advice, blood glucose monitoring, and insulin therapy has been shown to help achieve glycemic control and reduce the rate of serious perinatal complications, including fetal death, shoulder dystocia bone fracture, and brachial nerve palsy.19

Metformin is more likely to cross the placenta than glyburide. Although metformin is associated with lower risk of neonatal hypoglycemia and less maternal weight gain than insulin, it may increase the risk of premature birth.20 A 2015 systematic review found that glyburide is associated with higher rates of neonatal hypoglycemia and macrosomia than insulin or metformin.20 In the umbilical cord plasma, concentration of glyburide is about 70% of maternal levels.21 Long-term safety data do not exist for metformin and glyburide.7 Data are insufficient to compare one oral therapy with the other and the decision usually is based on clinical preference, availability, and national clinical practice guidelines.22 According to ADA guidelines, both oral agents are recommended as second-line choices to insulin because they cross the placenta.7


Glycemic control is key for preventing further complications secondary to gestational diabetes. Patients should self-monitor their fasting and postprandial glucose levels to achieve glycemic control.7 The ADA's recommended targets for women with gestational diabetes are similar to those of ACOG: for fasting glucose to be less than 95 mg/dL and for 1-hour postprandial glucose to be less than 140 mg/dL or 2-hour postprandial glucose be less than 120 mg/dL.7

A1C is used as a secondary measure of glycemic control in pregnancy after self-monitoring of blood glucose. This is because A1C does not provide information on postprandial hyperglycemia, a cause of fetal macrosomia.7 In the second and third trimester, an A1C of 6.5% or greater increases the risk of adverse outcomes for mother and fetus.7 AlC tends to be slightly lower than normal in pregnant than nonpregnant women because of increased red blood cell turnover. The target of 6% to 6.5% is recommended, although 6% is optimal as pregnancy progresses.7


Complications of gestational diabetes for the fetus and infant include spontaneous abortion, fetal anomalies, fetal demise, preeclampsia, macrosomia, cesarean delivery, neonatal hypoglycemia, and neonatal hyperbilirubinemia. In addition, intrauterine exposure to diabetes increases the fetus's risk of obesity and type 2 diabetes.23

Perinatal and postpartum complications with gestational diabetes do not appear to affect women of all races or ethnicities proportionally. One study showed that although Asian women have a higher rate of gestational diabetes, their pregnancies are at lower risk of adverse perinatal outcomes of gestational diabetes.24 A study assessed whether socioeconomic status, race/ethnicity, or prenatal cardiometabolic disease affect postpartum cardiometabolic risk.25 Researchers found that low- to middle-income black women had a higher postpartum cardiometabolic risk, compared with non-Hispanic white and Hispanic women.25

For the mother, gestational diabetes is significantly associated with an increased risk of developing a postpartum disorder of glucose metabolism.26 A 7-year study found that nearly 20% of women diagnosed with gestational diabetes are later diagnosed with diabetes.1 In another study, the hazard ratio (95%) of diabetes for black women was significantly higher at 9.9 (7.5, 13.1) than that for Asian/Pacific Islanders at 6.3 (5, 7.9), non-Hispanic white women at 6.5 (6.8, 8.7), and Hispanic women at 7.7 (6.8, 8.7), which shows that racial and ethnic disparities exist in women's risk of developing diabetes after gestational diabetes.27 Women at risk for developing type 2 diabetes, including those with a history of gestational diabetes, should consider enrolling in the evidence-based Diabetes Prevention Program to delay or prevent the diagnosis of type 2 diabetes.


Gestational diabetes increases the risk of fetal complications and postpartum maternal development of type 2 diabetes. Pregnant women should expect screening at 24 to 28 weeks with an oral fasting glucose tolerance test. Clinicians must consider lifelong screening of patients for prediabetes and diabetes postpartum so that immediate interventions can be made to prevent disease progression and further complications. Racial disparities in postpartum complications and maternal development of type 2 diabetes from gestational diabetes highlight the need for screening and prevention, especially for women in high-risk ethnic groups.


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gestational diabetes; pregnancy; screening; American Diabetes Association; glucose tolerance; type 2 diabetes

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